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Bibliography on: Topologically Associating Domains

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Robert J. Robbins is a biologist, an educator, a science administrator, a publisher, an information technologist, and an IT leader and manager who specializes in advancing biomedical knowledge and supporting education through the application of information technology. More About:  RJR | OUR TEAM | OUR SERVICES | THIS WEBSITE

RJR: Recommended Bibliography 26 Nov 2020 at 01:51 Created: 

Topologically Associating Domains

"Recent studies have shown that chromosomes in a range of organisms are compartmentalized in different types of chromatin domains. In mammals, chromosomes form compartments that are composed of smaller Topologically Associating Domains (TADs). TADs are thought to represent functional domains of gene regulation but much is still unknown about the mechanisms of their formation and how they exert their regulatory effect on embedded genes. Further, similar domains have been detected in other organisms, including flies, worms, fungi and bacteria. Although in all these cases these domains appear similar as detected by 3C-based methods, their biology appears to be quite distinct with differences in the protein complexes involved in their formation and differences in their internal organization." QUOTE FROM: Dekker Job and Heard Edith (2015), Structural and functional diversity of Topologically Associating Domains, FEBS Letters, 589, doi: 10.1016/j.febslet.2015.08.044

Created with PubMed® Query: "Topologically Associating Domains" OR "Topologically Associating Domain" NOT pmcbook NOT ispreviousversion

Citations The Papers (from PubMed®)

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RevDate: 2020-11-24

Rodríguez-Carballo E, Lopez-Delisle L, Willemin A, et al (2020)

Chromatin topology and the timing of enhancer function at the HoxD locus.

Proceedings of the National Academy of Sciences of the United States of America [Epub ahead of print].

The HoxD gene cluster is critical for proper limb formation in tetrapods. In the emerging limb buds, different subgroups of Hoxd genes respond first to a proximal regulatory signal, then to a distal signal that organizes digits. These two regulations are exclusive from one another and emanate from two distinct topologically associating domains (TADs) flanking HoxD, both containing a range of appropriate enhancer sequences. The telomeric TAD (T-DOM) contains several enhancers active in presumptive forearm cells and is divided into two sub-TADs separated by a CTCF-rich boundary, which defines two regulatory submodules. To understand the importance of this particular regulatory topology to control Hoxd gene transcription in time and space, we either deleted or inverted this sub-TAD boundary, eliminated the CTCF binding sites, or inverted the entire T-DOM to exchange the respective positions of the two sub-TADs. The effects of such perturbations on the transcriptional regulation of Hoxd genes illustrate the requirement of this regulatory topology for the precise timing of gene activation. However, the spatial distribution of transcripts was eventually resumed, showing that the presence of enhancer sequences, rather than either their exact topology or a particular chromatin architecture, is the key factor. We also show that the affinity of enhancers to find their natural target genes can overcome the presence of both a strong TAD border and an unfavorable orientation of CTCF sites.

RevDate: 2020-11-18

Eres IE, Y Gilad (2020)

A TAD Skeptic: Is 3D Genome Topology Conserved?.

Trends in genetics : TIG pii:S0168-9525(20)30298-5 [Epub ahead of print].

The notion that topologically associating domains (TADs) are highly conserved across species is prevalent in the field of 3D genomics. However, what exactly is meant by 'highly conserved' and what are the actual comparative data that support this notion? To address these questions, we performed a historical review of the relevant literature and retraced numerous citation chains to reveal the primary data that were used as the basis for the widely accepted conclusion that TADs are highly conserved across evolution. A thorough review of the available evidence suggests the answer may be more complex than what is commonly presented.

RevDate: 2020-11-13

Ehrlich KC, Baribault C, M Ehrlich (2020)

Epigenetics of Muscle- and Brain-Specific Expression of KLHL Family Genes.

International journal of molecular sciences, 21(21): pii:ijms21218394.

KLHL and the related KBTBD genes encode components of the Cullin-E3 ubiquitin ligase complex and typically target tissue-specific proteins for degradation, thereby affecting differentiation, homeostasis, metabolism, cell signaling, and the oxidative stress response. Despite their importance in cell function and disease (especially, KLHL40, KLHL41, KBTBD13, KEAP1, and ENC1), previous studies of epigenetic factors that affect transcription were predominantly limited to promoter DNA methylation. Using diverse tissue and cell culture whole-genome profiles, we examined 17 KLHL or KBTBD genes preferentially expressed in skeletal muscle or brain to identify tissue-specific enhancer and promoter chromatin, open chromatin (DNaseI hypersensitivity), and DNA hypomethylation. Sixteen of the 17 genes displayed muscle- or brain-specific enhancer chromatin in their gene bodies, and most exhibited specific intergenic enhancer chromatin as well. Seven genes were embedded in super-enhancers (particularly strong, tissue-specific clusters of enhancers). The enhancer chromatin regions typically displayed foci of DNA hypomethylation at peaks of open chromatin. In addition, we found evidence for an intragenic enhancer in one gene upregulating expression of its neighboring gene, specifically for KLHL40/HHATL and KLHL38/FBXO32 gene pairs. Many KLHL/KBTBD genes had tissue-specific promoter chromatin at their 5' ends, but surprisingly, two (KBTBD11 and KLHL31) had constitutively unmethylated promoter chromatin in their 3' exons that overlaps a retrotransposed KLHL gene. Our findings demonstrate the importance of expanding epigenetic analyses beyond the 5' ends of genes in studies of normal and abnormal gene regulation.

RevDate: 2020-11-06

Chang L, Li M, Shao S, et al (2020)

Nuclear peripheral chromatin-lamin B1 interaction is required for global integrity of chromatin architecture and dynamics in human cells.

Protein & cell pii:10.1007/s13238-020-00794-8 [Epub ahead of print].

The eukaryotic genome is folded into higher-order conformation accompanied with constrained dynamics for coordinated genome functions. However, the molecular machinery underlying these hierarchically organized three-dimensional (3D) chromatin architecture and dynamics remains poorly understood. Here by combining imaging and sequencing, we studied the role of lamin B1 in chromatin architecture and dynamics. We found that lamin B1 depletion leads to detachment of lamina-associated domains (LADs) from the nuclear periphery accompanied with global chromatin redistribution and decompaction. Consequently, the inter-chromosomal as well as inter-compartment interactions are increased, but the structure of topologically associating domains (TADs) is not affected. Using live-cell genomic loci tracking, we further proved that depletion of lamin B1 leads to increased chromatin dynamics, owing to chromatin decompaction and redistribution toward nucleoplasm. Taken together, our data suggest that lamin B1 and chromatin interactions at the nuclear periphery promote LAD maintenance, chromatin compaction, genomic compartmentalization into chromosome territories and A/B compartments and confine chromatin dynamics, supporting their crucial roles in chromatin higher-order structure and chromatin dynamics.

RevDate: 2020-11-06

Nora EP, Caccianini L, Fudenberg G, et al (2020)

Molecular basis of CTCF binding polarity in genome folding.

Nature communications, 11(1):5612 pii:10.1038/s41467-020-19283-x.

Current models propose that boundaries of mammalian topologically associating domains (TADs) arise from the ability of the CTCF protein to stop extrusion of chromatin loops by cohesin. While the orientation of CTCF motifs determines which pairs of CTCF sites preferentially stabilize loops, the molecular basis of this polarity remains unclear. By combining ChIP-seq and single molecule live imaging we report that CTCF positions cohesin, but does not control its overall binding dynamics on chromatin. Using an inducible complementation system, we find that CTCF mutants lacking the N-terminus cannot insulate TADs properly. Cohesin remains at CTCF sites in this mutant, albeit with reduced enrichment. Given the orientation of CTCF motifs presents the N-terminus towards cohesin as it translocates from the interior of TADs, these observations explain how the orientation of CTCF binding sites translates into genome folding patterns.

RevDate: 2020-11-05

Kong N, I Jung (2020)

Long-range chromatin interactions in pathogenic gene expression control.

Transcription [Epub ahead of print].

A large number of distal cis-regulatory elements (cREs) have been annotated in the human genome, which plays a central role in orchestrating spatiotemporal gene expression. Since many cREs regulate non-adjacent genes, long-range cRE-promoter interactions are an important factor in the functional characterization of the engaged cREs. In this regard, recent studies have demonstrated that identification of long-range target genes can decipher the effect of genetic mutations residing within cREs on abnormal gene expression. In addition, investigation of altered long-range cREs-promoter interactions induced by chromosomal rearrangements has revealed their critical roles in pathogenic gene expression. In this review, we briefly discuss how the analysis of 3D chromatin structure can help us understand the functional impact of cREs harboring disease-associated genetic variants and how chromosomal rearrangements disrupting topologically associating domains can lead to pathogenic gene expression.

RevDate: 2020-10-26

Chu X, J Wang (2020)

Microscopic Chromosomal Structural and Dynamical Origin of Cell Differentiation and Reprogramming.

Advanced science (Weinheim, Baden-Wurttemberg, Germany), 7(20):2001572 pii:ADVS2006.

As an essential and fundamental process of life, cell development involves large-scale reorganization of the 3D genome architecture, which forms the basis of gene regulation. Here, a landscape-switching model is developed to explore the microscopic chromosomal structural origin of embryonic stem cell (ESC) differentiation and somatic cell reprogramming. It is shown that chromosome structure exhibits significant compartment-switching in the unit of topologically associating domain. It is found that the chromosome during differentiation undergoes monotonic compaction with spatial repositioning of active and inactive chromosomal loci toward the chromosome surface and interior, respectively. In contrast, an overexpanded chromosome, which exhibits universal localization of loci at the chromosomal surface with erasing the structural characteristics formed in the somatic cells, is observed during reprogramming. An early distinct differentiation pathway from the ESC to the terminally differentiated cell, giving rise to early bifurcation on the Waddington landscape for the ESC differentiation is suggested. The theoretical model herein including the non-equilibrium effects, draws a picture of the highly irreversible cell differentiation and reprogramming processes, in line with the experiments. The predictions provide a physical understanding of cell differentiation and reprogramming from the chromosomal structural and dynamical perspective and can be tested by future experiments.

RevDate: 2020-10-25

Li Y, Gao G, Lin Y, et al (2020)

Pacific Biosciences assembly with Hi-C mapping generates an improved, chromosome-level goose genome.

GigaScience, 9(10):.

BACKGROUND: The domestic goose is an economically important and scientifically valuable waterfowl; however, a lack of high-quality genomic data has hindered research concerning its genome, genetics, and breeding. As domestic geese breeds derive from both the swan goose (Anser cygnoides) and the graylag goose (Anser anser), we selected a female Tianfu goose for genome sequencing. We generated a chromosome-level goose genome assembly by adopting a hybrid de novo assembly approach that combined Pacific Biosciences single-molecule real-time sequencing, high-throughput chromatin conformation capture mapping, and Illumina short-read sequencing.

FINDINGS: We generated a 1.11-Gb goose genome with contig and scaffold N50 values of 1.85 and 33.12 Mb, respectively. The assembly contains 39 pseudo-chromosomes (2n = 78) accounting for ∼88.36% of the goose genome. Compared with previous goose assemblies, our assembly has more continuity, completeness, and accuracy; the annotation of core eukaryotic genes and universal single-copy orthologs has also been improved. We have identified 17,568 protein-coding genes and a repeat content of 8.67% (96.57 Mb) in this genome assembly. We also explored the spatial organization of chromatin and gene expression in the goose liver tissues, in terms of inter-pseudo-chromosomal interaction patterns, compartments, topologically associating domains, and promoter-enhancer interactions.

CONCLUSIONS: We present the first chromosome-level assembly of the goose genome. This will be a valuable resource for future genetic and genomic studies on geese.

RevDate: 2020-10-22

Gu B, Comerci CJ, McCarthy DG, et al (2020)

Opposing Effects of Cohesin and Transcription on CTCF Organization Revealed by Super-resolution Imaging.

Molecular cell pii:S1097-2765(20)30684-5 [Epub ahead of print].

CCCTC-binding factor (CTCF) and cohesin play critical roles in organizing mammalian genomes into topologically associating domains (TADs). Here, by combining genetic engineering with quantitative super-resolution stimulated emission depletion (STED) microscopy, we demonstrate that in living cells, CTCF forms clusters typically containing 2-8 molecules. A fraction of CTCF clusters, enriched for those with ≥3 molecules, are coupled with cohesin complexes with a characteristic physical distance suggestive of a defined molecular interaction. Acute degradation of the cohesin unloader WAPL or transcriptional inhibition (TI) result in increased CTCF clustering. Furthermore, the effect of TI on CTCF clusters is alleviated by the acute loss of the cohesin subunit SMC3. Our study provides quantitative characterization of CTCF clusters in living cells, uncovers the opposing effects of cohesin and transcription on CTCF clustering, and highlights the power of quantitative super-resolution microscopy as a tool to bridge the gap between biochemical and genomic methodologies in chromatin research.

RevDate: 2020-10-22

Tinker RJ, Burghel GJ, Garg S, et al (2020)

Haploinsufficiency of ATP6V0C possibly underlies 16p13.3 deletions that cause microcephaly, seizures, and neurodevelopmental disorder.

We recently contributed to the description of eight individuals with a novel condition caused by 16p13.3 microdeletions encompassing TBC1D24, ATP6V0C, and PDPK1 and resulting in epilepsy, microcephaly and neurodevelopmental problems. The phenotypic spectrum, the minimum overlapping region and the underlying disease mechanism for this disorder remain to be clarified. Here we report a 3.5-year-old male, with microcephaly, autism spectrum disorder and a de novo 16p13.3 microdeletion. We performed detailed in silico analysis to show that the minimum overlapping region for the condition is ~80Kb encompassing five protein coding genes. Analysis of loss of function constraint metrics, transcript-aware evaluation of the population variants, GeVIR scores, analysis of reported pathogenic point variants, detailed review of the known functions of gene products and their animal models showed that the haploinsufficiency of ATP6V0C likely underlies the phenotype of this condition. Protein-protein interaction network, gene phenology and analysis of topologically associating domain showed that it was unlikely that the disorder has an epistatic or regulatory basis. 16p13.3 deletions encompassing ATP6V0C cause a neurodevelopmental disorder. Our results broaden the phenotypic spectrum of this disorder and clarify the likely underlying disease mechanism for the condition.

RevDate: 2020-10-20

Szabo Q, Donjon A, Jerković I, et al (2020)

Regulation of single-cell genome organization into TADs and chromatin nanodomains.

Nature genetics pii:10.1038/s41588-020-00716-8 [Epub ahead of print].

The genome folds into a hierarchy of three-dimensional structures within the nucleus. At the sub-megabase scale, chromosomes form topologically associating domains (TADs)1-4. However, how TADs fold in single cells is elusive. Here, we reveal TAD features inaccessible to cell population analysis by using super-resolution microscopy. TAD structures and physical insulation associated with their borders are variable between individual cells, yet chromatin intermingling is enriched within TADs compared to adjacent TADs in most cells. The spatial segregation of TADs is further exacerbated during cell differentiation. Favored interactions within TADs are regulated by cohesin and CTCF through distinct mechanisms: cohesin generates chromatin contacts and intermingling while CTCF prevents inter-TAD contacts. Furthermore, TADs are subdivided into discrete nanodomains, which persist in cells depleted of CTCF or cohesin, whereas disruption of nucleosome contacts alters their structural organization. Altogether, these results provide a physical basis for the folding of individual chromosomes at the nanoscale.

RevDate: 2020-10-19

Huang Y, Neijts R, W de Laat (2020)

How chromosome topologies get their shape: views from proximity ligation and microscopy methods.

FEBS letters [Epub ahead of print].

The three-dimensional organization of our genome is an important determinant for the transcriptional output of a gene in (patho)physiological contexts. The spatial organization of linear chromosomes within nucleus is dominantly inferred using two distinct approaches, chromosome conformation capture (3C) and DNA fluorescent in situ hybridization (DNA-FISH). While 3C and its derivatives score genomic interaction frequencies based on proximity ligation events, DNA-FISH methods measure physical distances between genomic loci. Despite these approaches probe different characteristics of chromosomal topologies, they provide a coherent picture of how chromosomes are organized in higher-order structures encompassing chromosome territories, compartments and topologically associating domains. Yet, at the finer topological level of promoter-enhancer communication, the imaging-centered and the 3C methods give more divergent and sometimes seemingly paradoxical results. Here, we compare and contrast observations made applying visual DNA-FISH and molecular 3C approaches. We emphasize that the 3C approach, due to its inherently competitive ligation step, measures only 'relative' proximities. A 3C interaction enriched between loci, therefore does not necessarily translates into a decrease in absolute spatial distance. Hence, we advocate caution when modelling chromosome conformations.

RevDate: 2020-10-16

Iwasaki Y, Ikemura T, Kurokawa K, et al (2020)

Implication of a new function of human tDNAs in chromatin organization.

Scientific reports, 10(1):17440 pii:10.1038/s41598-020-74499-7.

Transfer RNA genes (tDNAs) are essential genes that encode tRNAs in all species. To understand new functions of tDNAs, other than that of encoding tRNAs, we used ENCODE data to examine binding characteristics of transcription factors (TFs) for all tDNA regions (489 loci) in the human genome. We divided the tDNAs into three groups based on the number of TFs that bound to them. At the two extremes were tDNAs to which many TFs bound (Group 1) and those to which no TFs bound (Group 3). Several TFs involved in chromatin remodeling such as ATF3, EP300 and TBL1XR1 bound to almost all Group 1 tDNAs. Furthermore, almost all Group 1 tDNAs included DNase I hypersensitivity sites and may thus interact with other chromatin regions through their bound TFs, and they showed highly conserved synteny across tetrapods. In contrast, Group 3 tDNAs did not possess these characteristics. These data suggest the presence of a previously uncharacterized function of these tDNAs. We also examined binding of CTCF to tDNAs and their involvement in topologically associating domains (TADs) and lamina-associated domains (LADs), which suggest a new perspective on the evolution and function of tDNAs.

RevDate: 2020-10-10

Saha P, Sowpati DT, Soujanya M, et al (2020)

Interplay of pericentromeric genome organization and chromatin landscape regulates the expression of Drosophila melanogaster heterochromatic genes.

Epigenetics & chromatin, 13(1):41.

BACKGROUND: Transcription of genes residing within constitutive heterochromatin is paradoxical to the tenets of epigenetic code. The regulatory mechanisms of Drosophila melanogaster heterochromatic gene transcription remain largely unknown. Emerging evidence suggests that genome organization and transcriptional regulation are inter-linked. However, the pericentromeric genome organization is relatively less studied. Therefore, we sought to characterize the pericentromeric genome organization and understand how this organization along with the pericentromeric factors influences heterochromatic gene expression.

RESULTS: Here, we characterized the pericentromeric genome organization in Drosophila melanogaster using 5C sequencing. Heterochromatic topologically associating domains (Het TADs) correlate with distinct epigenomic domains of active and repressed heterochromatic genes at the pericentromeres. These genes are known to depend on the heterochromatic landscape for their expression. However, HP1a or Su(var)3-9 RNAi has minimal effects on heterochromatic gene expression, despite causing significant changes in the global Het TAD organization. Probing further into this observation, we report the role of two other chromatin proteins enriched at the pericentromeres-dMES-4 and dADD1 in regulating the expression of a subset of heterochromatic genes.

CONCLUSIONS: Distinct pericentromeric genome organization and chromatin landscapes maintained by the interplay of heterochromatic factors (HP1a, H3K9me3, dMES-4 and dADD1) are sufficient to support heterochromatic gene expression despite the loss of global Het TAD structure. These findings open new avenues for future investigations into the mechanisms of heterochromatic gene expression.

RevDate: 2020-10-06

de Bruijn SE, Fiorentino A, Ottaviani D, et al (2020)

Structural Variants Create New Topological-Associated Domains and Ectopic Retinal Enhancer-Gene Contact in Dominant Retinitis Pigmentosa.

American journal of human genetics pii:S0002-9297(20)30322-0 [Epub ahead of print].

The cause of autosomal-dominant retinitis pigmentosa (adRP), which leads to loss of vision and blindness, was investigated in families lacking a molecular diagnosis. A refined locus for adRP on Chr17q22 (RP17) was delineated through genotyping and genome sequencing, leading to the identification of structural variants (SVs) that segregate with disease. Eight different complex SVs were characterized in 22 adRP-affected families with >300 affected individuals. All RP17 SVs had breakpoints within a genomic region spanning YPEL2 to LINC01476. To investigate the mechanism of disease, we reprogrammed fibroblasts from affected individuals and controls into induced pluripotent stem cells (iPSCs) and differentiated them into photoreceptor precursor cells (PPCs) or retinal organoids (ROs). Hi-C was performed on ROs, and differential expression of regional genes and a retinal enhancer RNA at this locus was assessed by qPCR. The epigenetic landscape of the region, and Hi-C RO data, showed that YPEL2 sits within its own topologically associating domain (TAD), rich in enhancers with binding sites for retinal transcription factors. The Hi-C map of RP17 ROs revealed creation of a neo-TAD with ectopic contacts between GDPD1 and retinal enhancers, and modeling of all RP17 SVs was consistent with neo-TADs leading to ectopic retinal-specific enhancer-GDPD1 accessibility. qPCR confirmed increased expression of GDPD1 and increased expression of the retinal enhancer that enters the neo-TAD. Altered TAD structure resulting in increased retinal expression of GDPD1 is the likely convergent mechanism of disease, consistent with a dominant gain of function. Our study highlights the importance of SVs as a genomic mechanism in unsolved Mendelian diseases.

RevDate: 2020-10-06

Akdemir KC, Le VT, Kim JM, et al (2020)

Somatic mutation distributions in cancer genomes vary with three-dimensional chromatin structure.

Nature genetics pii:10.1038/s41588-020-0708-0 [Epub ahead of print].

Somatic mutations in driver genes may ultimately lead to the development of cancer. Understanding how somatic mutations accumulate in cancer genomes and the underlying factors that generate somatic mutations is therefore crucial for developing novel therapeutic strategies. To understand the interplay between spatial genome organization and specific mutational processes, we studied 3,000 tumor-normal-pair whole-genome datasets from 42 different human cancer types. Our analyses reveal that the change in somatic mutational load in cancer genomes is co-localized with topologically-associating-domain boundaries. Domain boundaries constitute a better proxy to track mutational load change than replication timing measurements. We show that different mutational processes lead to distinct somatic mutation distributions where certain processes generate mutations in active domains, and others generate mutations in inactive domains. Overall, the interplay between three-dimensional genome organization and active mutational processes has a substantial influence on the large-scale mutation-rate variations observed in human cancers.

RevDate: 2020-09-28

Goel VY, AS Hansen (2020)

The macro and micro of chromosome conformation capture.

Wiley interdisciplinary reviews. Developmental biology [Epub ahead of print].

The 3D organization of the genome facilitates gene regulation, replication, and repair, making it a key feature of genomic function and one that remains to be properly understood. Over the past two decades, a variety of chromosome conformation capture (3C) methods have delineated genome folding from megabase-scale compartments and topologically associating domains (TADs) down to kilobase-scale enhancer-promoter interactions. Understanding the functional role of each layer of genome organization is a gateway to understanding cell state, development, and disease. Here, we discuss the evolution of 3C-based technologies for mapping 3D genome organization. We focus on genomics methods and provide a historical account of the development from 3C to Hi-C. We also discuss ChIP-based techniques that focus on 3D genome organization mediated by specific proteins, capture-based methods that focus on particular regions or regulatory elements, 3C-orthogonal methods that do not rely on restriction digestion and proximity ligation, and methods for mapping the DNA-RNA and RNA-RNA interactomes. We consider the biological discoveries that have come from these methods, examine the mechanistic contributions of CTCF, cohesin, and loop extrusion to genomic folding, and detail the 3D genome field's current understanding of nuclear architecture. Finally, we give special consideration to Micro-C as an emerging frontier in chromosome conformation capture and discuss recent Micro-C findings uncovering fine-scale chromatin organization in unprecedented detail. This article is categorized under: Gene Expression and Transcriptional Hierarchies > Regulatory Mechanisms Gene Expression and Transcriptional Hierarchies > Gene Networks and Genomics.

RevDate: 2020-10-13

Xie WJ, Qi Y, B Zhang (2020)

Characterizing chromatin folding coordinate and landscape with deep learning.

PLoS computational biology, 16(9):e1008262 pii:PCOMPBIOL-D-20-00738.

Genome organization is critical for setting up the spatial environment of gene transcription, and substantial progress has been made towards its high-resolution characterization. The underlying molecular mechanism for its establishment is much less understood. We applied a deep-learning approach, variational autoencoder (VAE), to analyze the fluctuation and heterogeneity of chromatin structures revealed by single-cell imaging and to identify a reaction coordinate for chromatin folding. This coordinate connects the seemingly random structures observed in individual cohesin-depleted cells as intermediate states along a folding pathway that leads to the formation of topologically associating domains (TAD). We showed that folding into wild-type-like structures remain energetically favorable in cohesin-depleted cells, potentially as a result of the phase separation between the two chromatin segments with active and repressive histone marks. The energetic stabilization, however, is not strong enough to overcome the entropic penalty, leading to the formation of only partially folded structures and the disappearance of TADs from contact maps upon averaging. Our study suggests that machine learning techniques, when combined with rigorous statistical mechanical analysis, are powerful tools for analyzing structural ensembles of chromatin.

RevDate: 2020-09-24

Chan WF, Coughlan HD, Iannarella N, et al (2020)

Identification and characterization of the long non-coding RNA Gm13218 as a novel regulator of Gata3.

Immunology and cell biology [Epub ahead of print].

The eukaryotic genome is three-dimensionally segregated into discrete globules of topologically associating domains (TADs), within which numerous cis-regulatory elements such as enhancers and promoters interact to regulate gene expression. In this study, we identify a T cell-specific sub-TAD containing the Gata3 locus, and reveal a previously uncharacterised long non-coding RNA (lncRNA) Gm13218 within a distant enhancer lying approximately 280 kilobases downstream of Gata3. Gm13218 expression is highly correlated with that of Gata3 during early immune system development and T helper 2 (TH 2) cell differentiation. Inhibition and overexpression of Gm13218 suggest that it may be involved in the establishment, but not the maintenance of Gata3 expression. Overall, we propose that Gm13218 is a novel regulator of Gata3 and may inform therapeutic strategies in diseases such allergy and lymphoma where Gata3 has a pathological role.

RevDate: 2020-09-28

Wang YXR, Sarkar P, Ursu O, et al (2019)

NETWORK MODELLING OF TOPOLOGICAL DOMAINS USING HI-C DATA.

The annals of applied statistics, 13(3):1511-1536.

Chromosome conformation capture experiments such as Hi-C are used to map the three-dimensional spatial organization of genomes. One specific feature of the 3D organization is known as topologically associating domains (TADs), which are densely interacting, contiguous chromatin regions playing important roles in regulating gene expression. A few algorithms have been proposed to detect TADs. In particular, the structure of Hi-C data naturally inspires application of community detection methods. However, one of the drawbacks of community detection is that most methods take exchangeability of the nodes in the network for granted; whereas the nodes in this case, that is, the positions on the chromosomes, are not exchangeable. We propose a network model for detecting TADs using Hi-C data that takes into account this nonexchangeability. in addition, our model explicitly makes use of cell-type specific CTCF binding sites as biological covariates and can be used to identify conserved TADs across multiple cell types. The model leads to a likelihood objective that can be efficiently optimized via relaxation. We also prove that when suitably initialized, this model finds the underlying TAD structure with high probability. using simulated data, we show the advantages of our method and the caveats of popular community detection methods, such as spectral clustering, in this application. Applying our method to real Hi-C data, we demonstrate the domains identified have desirable epigenetic features and compare them across different cell types.

RevDate: 2020-10-13

Mitter M, Gasser C, Takacs Z, et al (2020)

Conformation of sister chromatids in the replicated human genome.

Nature, 586(7827):139-144.

The three-dimensional organization of the genome supports regulated gene expression, recombination, DNA repair, and chromosome segregation during mitosis. Chromosome conformation capture (Hi-C)1,2 analysis has revealed a complex genomic landscape of internal chromosomal structures in vertebrate cells3-7, but the identical sequence of sister chromatids has made it difficult to determine how they topologically interact in replicated chromosomes. Here we describe sister-chromatid-sensitive Hi-C (scsHi-C), which is based on labelling of nascent DNA with 4-thio-thymidine and nucleoside conversion chemistry. Genome-wide conformation maps of human chromosomes reveal that sister-chromatid pairs interact most frequently at the boundaries of topologically associating domains (TADs). Continuous loading of a dynamic cohesin pool separates sister-chromatid pairs inside TADs and is required to focus sister-chromatid contacts at TAD boundaries. We identified a subset of TADs that are overall highly paired and are characterized by facultative heterochromatin and insulated topological domains that form separately within individual sister chromatids. The rich pattern of sister-chromatid topologies and our scsHi-C technology will make it possible to investigate how physical interactions between identical DNA molecules contribute to DNA repair, gene expression, chromosome segregation, and potentially other biological processes.

RevDate: 2020-09-24

Miron E, Oldenkamp R, Brown JM, et al (2020)

Chromatin arranges in chains of mesoscale domains with nanoscale functional topography independent of cohesin.

Science advances, 6(39): pii:6/39/eaba8811.

Three-dimensional (3D) chromatin organization plays a key role in regulating mammalian genome function; however, many of its physical features at the single-cell level remain underexplored. Here, we use live- and fixed-cell 3D super-resolution and scanning electron microscopy to analyze structural and functional nuclear organization in somatic cells. We identify chains of interlinked ~200- to 300-nm-wide chromatin domains (CDs) composed of aggregated nucleosomes that can overlap with individual topologically associating domains and are distinct from a surrounding RNA-populated interchromatin compartment. High-content mapping uncovers confinement of cohesin and active histone modifications to surfaces and enrichment of repressive modifications toward the core of CDs in both hetero- and euchromatic regions. This nanoscale functional topography is temporarily relaxed in postreplicative chromatin but remarkably persists after ablation of cohesin. Our findings establish CDs as physical and functional modules of mesoscale genome organization.

RevDate: 2020-09-19

Fu AX, Lui KN, Tang CS, et al (2020)

Whole-genome analysis of noncoding genetic variations identifies multi-scale regulatory element perturbations associated with Hirschsprung disease.

Genome research pii:gr.264473.120 [Epub ahead of print].

It is widely recognized that noncoding genetic variants play important roles in many human diseases, but there are multiple challenges that hinder the identification of functional disease-associated noncoding variants. The number of noncoding variants can be many times of coding variants; many of them are not functional but in linkage disequilibrium with the functional ones; different variants can have epistatic effects; different variants can affect the same genes or pathways in different individuals; and some variants are related to each other not by affecting the same gene but by affecting the binding of the same upstream regulator. To overcome these difficulties, we propose a novel analysis framework that considers convergent impacts of different genetic variants on protein binding, which provides multi-scale information about disease-associated perturbations of regulatory elements, genes, and pathways. Applying it to our whole-genome sequencing data of 918 short-segment Hirschsprung disease patients and matched controls, we identify various novel genes not detected by standard single-variant and region-based tests, functionally centering on neural crest migration and development. Our framework also identifies upstream regulators whose binding is influenced by the noncoding variants. Using human neural crest cells, we confirm cell-stage-specific regulatory roles of three top novel regulatory elements on our list, respectively in the RET, RASGEF1A and PIK3C2B loci. In the PIK3C2B regulatory element, we further show that a noncoding variant found only in the patients affects the binding of the gliogenesis regulator NFIA, with a corresponding up-regulation of multiple genes in the same topologically associating domain.

RevDate: 2020-09-25

Serna-Pujol N, Salinas-Pena M, Mugianesi F, et al (2020)

TADs enriched in histone H1.2 strongly overlap with the B compartment, inaccessible chromatin, and AT-rich Giemsa bands.

The FEBS journal [Epub ahead of print].

Giemsa staining of metaphase chromosomes results in a characteristic banding useful for identification of chromosomes and its alterations. We have investigated in silico whether Giemsa bands (G bands) correlate with epigenetic and topological features of the interphase genome. Staining of G-positive bands decreases with GC content; nonetheless, G-negative bands are GC heterogeneous. High GC bands are enriched in active histone marks, RNA polymerase II, and SINEs and associate with gene richness, gene expression, and early replication. Low GC bands are enriched in repressive marks, lamina-associated domains, and LINEs. Histone H1 variants distribute heterogeneously among G bands: H1X is enriched at high GC bands and H1.2 is abundant at low GC, compacted bands. According to epigenetic features and H1 content, G bands can be organized in clusters useful to compartmentalize the genome. Indeed, we have obtained Hi-C chromosome interaction maps and compared topologically associating domains (TADs) and A/B compartments to G banding. TADs with high H1.2/H1X ratio strongly overlap with B compartment, late replicating, and inaccessible chromatin and low GC bands. We propose that GC content is a strong driver of chromatin compaction and 3D genome organization, that Giemsa staining recapitulates this organization denoted by high-throughput techniques, and that H1 variants distribute at distinct chromatin domains. DATABASES: Hi-C data on T47D breast cancer cells have been deposited in NCBI's Gene Expression Omnibus and are accessible through GEO Series accession number GSE147627.

RevDate: 2020-08-21

Forcato M, S Bicciato (2021)

Computational Analysis of Hi-C Data.

Methods in molecular biology (Clifton, N.J.), 2157:103-125.

The chromatin organization in the 3D nuclear space is essential for genome functionality. This spatial organization encompasses different topologies at diverse scale lengths with chromosomes occupying distinct volumes and individual chromosomes folding into compartments, inside which the chromatin fiber is packed in large domains (as the topologically associating domains, TADs) and forms short-range interactions (as enhancer-promoter loops). The widespread adoption of high-throughput techniques derived from chromosome conformation capture (3C) has been instrumental in investigating the nuclear organization of chromatin. In particular, Hi-C has the potential to achieve the most comprehensive characterization of chromatin 3D structures, as in principle it can detect any pair of restriction fragments connected as a result of ligation by proximity. However, the analysis of the enormous amount of genomic data produced by Hi-C techniques requires the application of complex, multistep computational procedures that may constitute a difficult task also for expert computational biologists. In this chapter, we describe the computational analysis of Hi-C data obtained from the lymphoblastoid cell line GM12878, detailing the processing of raw data, the generation and normalization of the Hi-C contact map, the detection of TADs and chromatin interactions, and their visualization and annotation.

RevDate: 2020-08-21

Di Stefano M, Castillo D, Serra F, et al (2021)

Analysis, Modeling, and Visualization of Chromosome Conformation Capture Experiments.

Methods in molecular biology (Clifton, N.J.), 2157:35-63.

Chromatin Conformation Capture techniques have unveiled several layers of chromosome organization such as the segregation in compartments, the folding in topologically associating domains (TADs), and site-specific looping interactions. The discovery of this genome hierarchical organization emerged from the computational analysis of chromatin capture data. With the increasing availability of such data, automatic pipelines for the robust comparison, grouping, and classification of multiple experiments are needed. Here we present a pipeline based on the TADbit framework that emphasizes reproducibility, automation, quality check, and statistical robustness. This comprehensive modular pipeline covers all the steps from the sequencing products to the visualization of reconstructed 3D models of the chromatin.

RevDate: 2020-09-15

Nath N, Hagenau L, Weiss S, et al (2020)

Genome-Wide DNA Alterations in X-Irradiated Human Gingiva Fibroblasts.

International journal of molecular sciences, 21(16):.

While ionizing radiation (IR) is a powerful tool in medical diagnostics, nuclear medicine, and radiology, it also is a serious threat to the integrity of genetic material. Mutagenic effects of IR to the human genome have long been the subject of research, yet still comparatively little is known about the genome-wide effects of IR exposure on the DNA-sequence level. In this study, we employed high throughput sequencing technologies to investigate IR-induced DNA alterations in human gingiva fibroblasts (HGF) that were acutely exposed to 0.5, 2, and 10 Gy of 240 kV X-radiation followed by repair times of 16 h or 7 days before whole-genome sequencing (WGS). Our analysis of the obtained WGS datasets revealed patterns of IR-induced variant (SNV and InDel) accumulation across the genome, within chromosomes as well as around the borders of topologically associating domains (TADs). Chromosome 19 consistently accumulated the highest SNVs and InDels events. Translocations showed variable patterns but with recurrent chromosomes of origin (e.g., Chr7 and Chr16). IR-induced InDels showed a relative increase in number relative to SNVs and a characteristic signature with respect to the frequency of triplet deletions in areas without repetitive or microhomology features. Overall experimental conditions and datasets the majority of SNVs per genome had no or little predicted functional impact with a maximum of 62, showing damaging potential. A dose-dependent effect of IR was surprisingly not apparent. We also observed a significant reduction in transition/transversion (Ti/Tv) ratios for IR-dependent SNVs, which could point to a contribution of the mismatch repair (MMR) system that strongly favors the repair of transitions over transversions, to the IR-induced DNA-damage response in human cells. Taken together, our results show the presence of distinguishable characteristic patterns of IR-induced DNA-alterations on a genome-wide level and implicate DNA-repair mechanisms in the formation of these signatures.

RevDate: 2020-08-18

Zhang X, Lei F, Wang XM, et al (2020)

NULP1 Alleviates Cardiac Hypertrophy by Suppressing NFAT3 Transcriptional Activity.

Journal of the American Heart Association, 9(16):e016419.

Background The development of pathological cardiac hypertrophy involves the coordination of a series of transcription activators and repressors, while their interplay to trigger pathological gene reprogramming remains unclear. NULP1 (nuclear localized protein 1) is a member of the basic helix-loop-helix family of transcription factors and its biological functions in pathological cardiac hypertrophy are barely understood. Methods and Results Immunoblot and immunostaining analyses showed that NULP1 expression was consistently reduced in the failing hearts of patients and hypertrophic mouse hearts and rat cardiomyocytes. Nulp1 knockout exacerbates aortic banding-induced cardiac hypertrophy pathology, which was significantly blunted by transgenic overexpression of Nulp1. Signal pathway screening revealed the nuclear factor of activated T cells (NFAT) pathway to be dramatically suppressed by NULP1. Coimmunoprecipitation showed that NULP1 directly interacted with the topologically associating domain of NFAT3 via its C-terminal region, which was sufficient to suppress NFAT3 transcriptional activity. Inactivation of the NFAT pathway by VIVIT peptides in vivo rescued the aggravated pathogenesis of cardiac hypertrophy resulting from Nulp1 deficiency. Conclusions NULP1 is an endogenous suppressor of NFAT3 signaling under hypertrophic stress and thus negatively regulates the pathogenesis of cardiac hypertrophy. Targeting overactivated NFAT by NULP1 may be a novel therapeutic strategy for the treatment of pathological cardiac hypertrophy and heart failure.

RevDate: 2020-08-22

Nanni L, Ceri S, C Logie (2020)

Spatial patterns of CTCF sites define the anatomy of TADs and their boundaries.

Genome biology, 21(1):197.

BACKGROUND: Topologically associating domains (TADs) are genomic regions of self-interaction. Additionally, it is known that TAD boundaries are enriched in CTCF binding sites. In turn, CTCF sites are known to be asymmetric, whereby the convergent configuration of a pair of CTCF sites leads to the formation of a chromatin loop in vivo. However, to date, it has been unclear how to reconcile TAD structure with CTCF-based chromatin loops.

RESULTS: We approach this problem by analysing CTCF binding site strengths and classifying clusters of CTCF sites along the genome on the basis of their relative orientation. Analysis of CTCF site orientation classes as a function of their spatial distribution along the human genome reveals that convergent CTCF site clusters are depleted while divergent CTCF clusters are enriched in the 5- to 100-kb range. We then analyse the distribution of CTCF binding sites as a function of TAD boundary conservation across seven primary human blood cell types. This reveals divergent CTCF site enrichment at TAD boundaries. Furthermore, convergent arrays of CTCF sites separate the left and right sections of TADs that harbour internal CTCF sites, resulting in unequal TAD 'halves'.

CONCLUSIONS: The orientation-based CTCF binding site cluster classification that we present reconciles TAD boundaries and CTCF site clusters in a mechanistically elegant fashion. This model suggests that the emergent structure of nuclear chromatin in the form of TADs relies on the obligate alternation of divergent and convergent CTCF site clusters that occur at different length scales along the genome.

RevDate: 2020-08-31

Khazeem MM, Cowell IG, Harkin LF, et al (2020)

Transcription of carbonyl reductase 1 is regulated by DNA topoisomerase II beta.

FEBS letters [Epub ahead of print].

DNA topoisomerase II beta (TOP2B) has a role in transcriptional regulation. Here, to further investigate transcriptional regulation by TOP2B, we used RNA-sequencing and real-time PCR to analyse the differential gene expression profiles of wild-type and two independent TOP2B-null pre-B Nalm-6 cell lines, one generated by targeted insertion and the other using CRISPR-Cas9 gene editing. We identified carbonyl reductase 1 (CBR1) among the most significantly downregulated genes in these TOP2B-null cells. Reduced CBR1 expression was accompanied by loss of binding of the transcription factors USF2 and MAX to the CBR1 promoter. We describe possible mechanisms by which loss of TOP2B results in CBR1 downregulation. To our knowledge, this is the first report of a link between TOP2B and CBR1.

RevDate: 2020-08-07

Heurteau A, Perrois C, Depierre D, et al (2020)

Insulator-based loops mediate the spreading of H3K27me3 over distant micro-domains repressing euchromatin genes.

Genome biology, 21(1):193.

RevDate: 2020-07-21

Matthews BJ, DJ Waxman (2020)

Impact of 3D genome organization, guided by cohesin and CTCF looping, on sex-biased chromatin interactions and gene expression in mouse liver.

Epigenetics & chromatin, 13(1):30.

Several thousand sex-differential distal enhancers have been identified in mouse liver; however, their links to sex-biased genes and the impact of any sex-differences in nuclear organization and chromatin interactions are unknown. To address these issues, we first characterized 1847 mouse liver genomic regions showing significant sex differential occupancy by cohesin and CTCF, two key 3D nuclear organizing factors. These sex-differential binding sites were primarily distal to sex-biased genes but rarely generated sex-differential TAD (topologically associating domain) or intra-TAD loop anchors, and were sometimes found in TADs without sex-biased genes. A substantial subset of sex-biased cohesin-non-CTCF binding sites, but not sex-biased cohesin-and-CTCF binding sites, overlapped sex-biased enhancers. Cohesin depletion reduced the expression of male-biased genes with distal, but not proximal, sex-biased enhancers by >10-fold, implicating cohesin in long-range enhancer interactions regulating sex-biased genes. Using circularized chromosome conformation capture-based sequencing (4C-seq), we showed that sex differences in distal sex-biased enhancer-promoter interactions are common. Intra-TAD loops with sex-independent cohesin-and-CTCF anchors conferred sex specificity to chromatin interactions indirectly, by insulating sex-biased enhancer-promoter contacts and by bringing sex-biased genes into closer proximity to sex-biased enhancers. Furthermore, sex-differential chromatin interactions involving sex-biased gene promoters, enhancers, and lncRNAs were associated with sex-biased binding of cohesin and/or CTCF. These studies elucidate how 3D genome organization impacts sex-biased gene expression in a non-reproductive tissue through both direct and indirect effects of cohesin and CTCF looping on distal enhancer interactions with sex-differentially expressed genes.

RevDate: 2020-07-14

Liang M, Soomro AU, Tasneem S, et al (2020)

Enhancer-gene rewiring in the pathogenesis of Quebec Platelet Disorder.

Blood pii:461326 [Epub ahead of print].

Quebec Platelet Disorder (QPD) is an autosomal dominant bleeding disorder with a unique, platelet-dependent gain-of-function defect in fibrinolysis, without systemic fibrinolysis. The hallmark feature of QPD is a >100-fold overexpression of PLAU specifically in megakaryocytes. This overexpression leads to >100-fold increased platelet stores of urokinase plasminogen activator (PLAU/uPA), subsequent plasmin-mediated degradation of diverse a-granule proteins, and platelet-dependent, accelerated fibrinolysis. The causative mutation is a 78kb tandem duplication of PLAU. How this duplication causes megakaryocyte-specific PLAU overexpression is unknown. To investigate the mechanism that causes QPD, we used epigenomic profiling, comparative genomics, and chromatin conformation capture approaches to study PLAU regulation in cultured megakaryocytes from QPD participants and unaffected controls. We show that the QPD duplication leads to ectopic interactions between PLAU and a conserved megakaryocyte enhancer found within the same topologically associating domain (TAD). Our results support a unique disease mechanism whereby the reorganization of subTAD genome architecture results in a dramatic, cell-type specific blood disorder phenotype.

RevDate: 2020-07-03

Danieli A, A Papantonis (2020)

Spatial genome architecture and the emergence of malignancy.

Human molecular genetics pii:5867002 [Epub ahead of print].

Human chromosomes are large spatially- and hierarchically-structured entities, the integrity of which needs to be preserved throughout the lifespan of the cell and in conjunction with cell cycle progression. Preservation of chromosomal structure is important for proper deployment of cell type-specific gene expression programs. Thus, aberrations in the integrity and structure of chromosomes will predictably lead to disease, including cancer. Here, we provide an updated standpoint with respect to chromatin misfolding and the emergence of various cancer types. We discuss recent studies implicating disruption of topologically-associating domains (TADs), switching between active and inactive compartments, rewiring of promoter-enhancer interactions in malignancy, as well as the effects of single nucleotide polymorphisms (SNPs) in non-coding regions involved in long-range regulatory interactions. In light of these findings, we argue that chromosome conformation studies may now also be useful for patient diagnosis and drug target discovery.

RevDate: 2020-08-31
CmpDate: 2020-08-31

Zhang K, Wu DY, Zheng H, et al (2020)

Analysis of Genome Architecture during SCNT Reveals a Role of Cohesin in Impeding Minor ZGA.

Molecular cell, 79(2):234-250.e9.

Somatic cell nuclear transfer (SCNT) can reprogram a somatic nucleus to a totipotent state. However, the re-organization of 3D chromatin structure in this process remains poorly understood. Using low-input Hi-C, we revealed that, during SCNT, the transferred nucleus first enters a mitotic-like state (premature chromatin condensation). Unlike fertilized embryos, SCNT embryos show stronger topologically associating domains (TADs) at the 1-cell stage. TADs become weaker at the 2-cell stage, followed by gradual consolidation. Compartments A/B are markedly weak in 1-cell SCNT embryos and become increasingly strengthened afterward. By the 8-cell stage, somatic chromatin architecture is largely reset to embryonic patterns. Unexpectedly, we found cohesin represses minor zygotic genome activation (ZGA) genes (2-cell-specific genes) in pluripotent and differentiated cells, and pre-depleting cohesin in donor cells facilitates minor ZGA and SCNT. These data reveal multi-step reprogramming of 3D chromatin architecture during SCNT and support dual roles of cohesin in TAD formation and minor ZGA repression.

RevDate: 2020-09-18

Luppino JM, Park DS, Nguyen SC, et al (2020)

Cohesin promotes stochastic domain intermingling to ensure proper regulation of boundary-proximal genes.

Nature genetics, 52(8):840-848.

The human genome can be segmented into topologically associating domains (TADs), which have been proposed to spatially sequester genes and regulatory elements through chromatin looping. Interactions between TADs have also been suggested, presumably because of variable boundary positions across individual cells. However, the nature, extent and consequence of these dynamic boundaries remain unclear. Here, we combine high-resolution imaging with Oligopaint technology to quantify the interaction frequencies across both weak and strong boundaries. We find that chromatin intermingling across population-defined boundaries is widespread but that the extent of permissibility is locus-specific. Cohesin depletion, which abolishes domain formation at the population level, does not induce ectopic interactions but instead reduces interactions across all boundaries tested. In contrast, WAPL or CTCF depletion increases inter-domain contacts in a cohesin-dependent manner. Reduced chromatin intermingling due to cohesin loss affects the topology and transcriptional bursting frequencies of genes near boundaries. We propose that cohesin occasionally bypasses boundaries to promote incorporation of boundary-proximal genes into neighboring domains.

RevDate: 2020-10-06

Chen SL, Hu F, Wang DW, et al (2020)

Prognosis and regulation of an adenylyl cyclase network in acute myeloid leukemia.

Aging, 12(12):11864-11877.

We explored the roles of adenylyl cyclases (ADCYs) in acute myeloid leukemia (AML). Expression ADCYs in AML and their effect on prognosis was analyzed using data from Oncomine, GEPIA and cBioPortal databases. Frequently altered neighbor genes (FANGs) of ADCYs were detected using the 3D Genome Browser, after which the functions of these FANGs were predicted using Metascape tools. Cell viability and apoptosis were assessed using CCK-8 and Annexin V-FITC/PI kits. Expression levels of ADCYs were higher in AML cells lines and in bone marrow-derived mononuclear cells from AML patients than in control cells, and were predictive of a poor prognosis. A total of 58 ADCY FANGs were identified from the topologically associating domains on the basis of the Hi-C data. Functional analysis of these FANGs revealed abnormal activation of the MAPK signaling pathway. Drug sensitivity tests showed that fasudil plus trametinib or sapanisertib had a synergistic effect suppressing AML cell viability and increasing apoptosis. These findings suggest that dysregulation of ADCY expression leads to altered signaling in the MAPK pathway in AML and that the ADCY expression profile may be predictive of prognosis in AML patients.

RevDate: 2020-08-20

Maharjan M, McKowen JK, CM Hart (2020)

Overlapping but Distinct Sequences Play Roles in the Insulator and Promoter Activities of the Drosophila BEAF-Dependent scs' Insulator.

Genetics, 215(4):1003-1012.

Chromatin domain insulators are thought to help partition the genome into genetic units called topologically associating domains (TADs). In Drosophila, TADs are often separated by inter-TAD regions containing active housekeeping genes and associated insulator binding proteins. This raises the question of whether insulator binding proteins are involved primarily in chromosomal TAD architecture or gene activation, or if these two activities are linked. The Boundary Element-Associated Factor of 32 kDa (BEAF-32, or BEAF for short) is usually found in inter-TADs. BEAF was discovered based on binding to the scs' insulator, and is important for the insulator activity of scs' and other BEAF binding sites. There are divergent promoters in scs' with a BEAF binding site by each. Here, we dissect the scs' insulator to identify DNA sequences important for insulator and promoter activity, focusing on the half of scs' with a high affinity BEAF binding site. We find that the BEAF binding site is important for both insulator and promoter activity, as is another sequence we refer to as LS4. Aside from that, different sequences play roles in insulator and promoter activity. So while there is overlap and BEAF is important for both, insulator and promoter activity can be separated.

RevDate: 2020-09-30
CmpDate: 2020-09-30

Stik G, Vidal E, Barrero M, et al (2020)

CTCF is dispensable for immune cell transdifferentiation but facilitates an acute inflammatory response.

Nature genetics, 52(7):655-661.

Three-dimensional organization of the genome is important for transcriptional regulation1-7. In mammals, CTCF and the cohesin complex create submegabase structures with elevated internal chromatin contact frequencies, called topologically associating domains (TADs)8-12. Although TADs can contribute to transcriptional regulation, ablation of TAD organization by disrupting CTCF or the cohesin complex causes modest gene expression changes13-16. In contrast, CTCF is required for cell cycle regulation17, embryonic development and formation of various adult cell types18. To uncouple the role of CTCF in cell-state transitions and cell proliferation, we studied the effect of CTCF depletion during the conversion of human leukemic B cells into macrophages with minimal cell division. CTCF depletion disrupts TAD organization but not cell transdifferentiation. In contrast, CTCF depletion in induced macrophages impairs the full-blown upregulation of inflammatory genes after exposure to endotoxin. Our results demonstrate that CTCF-dependent genome topology is not strictly required for a functional cell-fate conversion but facilitates a rapid and efficient response to an external stimulus.

RevDate: 2020-07-17

Kang H, Shokhirev MN, Xu Z, et al (2020)

Dynamic regulation of histone modifications and long-range chromosomal interactions during postmitotic transcriptional reactivation.

Genes & development, 34(13-14):913-930.

During mitosis, transcription of genomic DNA is dramatically reduced, before it is reactivated during nuclear reformation in anaphase/telophase. Many aspects of the underlying principles that mediate transcriptional memory and reactivation in the daughter cells remain unclear. Here, we used ChIP-seq on synchronized cells at different stages after mitosis to generate genome-wide maps of histone modifications. Combined with EU-RNA-seq and Hi-C analyses, we found that during prometaphase, promoters, enhancers, and insulators retain H3K4me3 and H3K4me1, while losing H3K27ac. Enhancers globally retaining mitotic H3K4me1 or locally retaining mitotic H3K27ac are associated with cell type-specific genes and their transcription factors for rapid transcriptional activation. As cells exit mitosis, promoters regain H3K27ac, which correlates with transcriptional reactivation. Insulators also gain H3K27ac and CCCTC-binding factor (CTCF) in anaphase/telophase. This increase of H3K27ac in anaphase/telophase is required for posttranscriptional activation and may play a role in the establishment of topologically associating domains (TADs). Together, our results suggest that the genome is reorganized in a sequential order, in which histone methylations occur first in prometaphase, histone acetylation, and CTCF in anaphase/telophase, transcription in cytokinesis, and long-range chromatin interactions in early G1. We thus provide insights into the histone modification landscape that allows faithful reestablishment of the transcriptional program and TADs during cell division.

RevDate: 2020-10-05

Papanicolaou N, A Bonetti (2020)

The New Frontier of Functional Genomics: From Chromatin Architecture and Noncoding RNAs to Therapeutic Targets.

SLAS discovery : advancing life sciences R & D, 25(6):568-580.

Common diseases are complex, multifactorial disorders whose pathogenesis is influenced by the interplay of genetic predisposition and environmental factors. Genome-wide association studies have interrogated genetic polymorphisms across genomes of individuals to test associations between genotype and susceptibility to specific disorders, providing insights into the genetic architecture of several complex disorders. However, genetic variants associated with the susceptibility to common diseases are often located in noncoding regions of the genome, such as tissue-specific enhancers or long noncoding RNAs, suggesting that regulatory elements might play a relevant role in human diseases. Enhancers are cis-regulatory genomic sequences that act in concert with promoters to regulate gene expression in a precise spatiotemporal manner. They can be located at a considerable distance from their cognate target promoters, increasing the difficulty of their identification. Genomes are organized in domains of chromatin folding, namely topologically associating domains (TADs). Identification of enhancer-promoter interactions within TADs has revealed principles of cell-type specificity across several organisms and tissues. The vast majority of mammalian genomes are pervasively transcribed, accounting for a previously unappreciated complexity of the noncoding RNA fraction. Particularly, long noncoding RNAs have emerged as key players for the establishment of chromatin architecture and regulation of gene expression. In this perspective, we describe the new advances in the fields of transcriptomics and genome organization, focusing on the role of noncoding genomic variants in the predisposition of common diseases. Finally, we propose a new framework for the identification of the next generation of pharmacological targets for common human diseases.

RevDate: 2020-08-17
CmpDate: 2020-08-17

Oudelaar AM, Beagrie RA, Gosden M, et al (2020)

Dynamics of the 4D genome during in vivo lineage specification and differentiation.

Nature communications, 11(1):2722 pii:10.1038/s41467-020-16598-7.

Mammalian gene expression patterns are controlled by regulatory elements, which interact within topologically associating domains (TADs). The relationship between activation of regulatory elements, formation of structural chromatin interactions and gene expression during development is unclear. Here, we present Tiled-C, a low-input chromosome conformation capture (3C) technique. We use this approach to study chromatin architecture at high spatial and temporal resolution through in vivo mouse erythroid differentiation. Integrated analysis of chromatin accessibility and single-cell expression data shows that regulatory elements gradually become accessible within pre-existing TADs during early differentiation. This is followed by structural re-organization within the TAD and formation of specific contacts between enhancers and promoters. Our high-resolution data show that these enhancer-promoter interactions are not established prior to gene expression, but formed gradually during differentiation, concomitant with progressive upregulation of gene activity. Together, these results provide new insight into the close, interdependent relationship between chromatin architecture and gene regulation during development.

RevDate: 2020-07-22

Sparks TM, Harabula I, A Pombo (2020)

Evolving methodologies and concepts in 4D nucleome research.

Current opinion in cell biology, 64:105-111.

The genome requires tight regulation in space and time to maintain viable cell functions. Advances in our understanding of the 3D genome show a complex hierarchical network of structures, involving compartments, membraneless bodies, topologically associating domains, lamina associated domains, protein- or RNA-mediated loops, enhancer-promoter contacts, and accessible chromatin regions, with chromatin state regulation through epigenetic and transcriptional mechanisms. Further technology developments are poised to increase genomic resolution, dissect single-cell behaviors, including in vivo dynamics of genome folding, and provide mechanistic perspectives that identify further 3D genome players by integrating multiomics information. We highlight recent key developments in 4D nucleome methodologies and give a perspective on their future directions.

RevDate: 2020-10-08
CmpDate: 2020-10-08

Melo US, Schöpflin R, Acuna-Hidalgo R, et al (2020)

Hi-C Identifies Complex Genomic Rearrangements and TAD-Shuffling in Developmental Diseases.

American journal of human genetics, 106(6):872-884.

Genome-wide analysis methods, such as array comparative genomic hybridization (CGH) and whole-genome sequencing (WGS), have greatly advanced the identification of structural variants (SVs) in the human genome. However, even with standard high-throughput sequencing techniques, complex rearrangements with multiple breakpoints are often difficult to resolve, and predicting their effects on gene expression and phenotype remains a challenge. Here, we address these problems by using high-throughput chromosome conformation capture (Hi-C) generated from cultured cells of nine individuals with developmental disorders (DDs). Three individuals had previously been identified as harboring duplications at the SOX9 locus and six had been identified with translocations. Hi-C resolved the positions of the duplications and was instructive in interpreting their distinct pathogenic effects, including the formation of new topologically associating domains (neo-TADs). Hi-C was very sensitive in detecting translocations, and it revealed previously unrecognized complex rearrangements at the breakpoints. In several cases, we observed the formation of fused-TADs promoting ectopic enhancer-promoter interactions that were likely to be involved in the disease pathology. In summary, we show that Hi-C is a sensible method for the detection of complex SVs in a clinical setting. The results help interpret the possible pathogenic effects of the SVs in individuals with DDs.

RevDate: 2020-06-05

Lazar JE, Stehling-Sun S, Nandakumar V, et al (2020)

Global Regulatory DNA Potentiation by SMARCA4 Propagates to Selective Gene Expression Programs via Domain-Level Remodeling.

Cell reports, 31(8):107676.

The human genome encodes millions of regulatory elements, of which only a small fraction are active within a given cell type. Little is known about the global impact of chromatin remodelers on regulatory DNA landscapes and how this translates to gene expression. We use precision genome engineering to reawaken homozygously inactivated SMARCA4, a central ATPase of the human SWI/SNF chromatin remodeling complex, in lung adenocarcinoma cells. Here, we combine DNase I hypersensitivity, histone modification, and transcriptional profiling to show that SMARCA4 dramatically increases both the number and magnitude of accessible chromatin sites genome-wide, chiefly by unmasking sites of low regulatory factor occupancy. By contrast, transcriptional changes are concentrated within well-demarcated remodeling domains wherein expression of specific genes is gated by both distal element activation and promoter chromatin configuration. Our results provide a perspective on how global chromatin remodeling activity is translated to gene expression via regulatory DNA.

RevDate: 2020-07-08

Boyle S, Flyamer IM, Williamson I, et al (2020)

A central role for canonical PRC1 in shaping the 3D nuclear landscape.

Genes & development, 34(13-14):931-949.

Polycomb group (PcG) proteins silence gene expression by chemically and physically modifying chromatin. A subset of PcG target loci are compacted and cluster in the nucleus; a conformation that is thought to contribute to gene silencing. However, how these interactions influence gross nuclear organization and their relationship with transcription remains poorly understood. Here we examine the role of Polycomb-repressive complex 1 (PRC1) in shaping 3D genome organization in mouse embryonic stem cells (mESCs). Using a combination of imaging and Hi-C analyses, we show that PRC1-mediated long-range interactions are independent of CTCF and can bridge sites at a megabase scale. Impairment of PRC1 enzymatic activity does not directly disrupt these interactions. We demonstrate that PcG targets coalesce in vivo, and that developmentally induced expression of one of the target loci disrupts this spatial arrangement. Finally, we show that transcriptional activation and the loss of PRC1-mediated interactions are separable events. These findings provide important insights into the function of PRC1, while highlighting the complexity of this regulatory system.

RevDate: 2020-08-12
CmpDate: 2020-08-12

Chen CH, Zheng R, Tokheim C, et al (2020)

Determinants of transcription factor regulatory range.

Nature communications, 11(1):2472 pii:10.1038/s41467-020-16106-x.

Characterization of the genomic distances over which transcription factor (TF) binding influences gene expression is important for inferring target genes from TF chromatin immunoprecipitation followed by sequencing (ChIP-seq) data. Here we systematically examine the relationship between thousands of TF and histone modification ChIP-seq data sets with thousands of gene expression profiles. We develop a model for integrating these data, which reveals two classes of TFs with distinct ranges of regulatory influence, chromatin-binding preferences, and auto-regulatory properties. We find that the regulatory range of the same TF bound within different topologically associating domains (TADs) depend on intrinsic TAD properties such as local gene density and G/C content, but also on the TAD chromatin states. Our results suggest that considering TF type, binding distance to gene locus, as well as chromatin context is important in identifying implicated TFs from GWAS SNPs.

RevDate: 2020-06-30

Sumiyama K, A Tanave (2020)

The regulatory landscape of the Dlx gene system in branchial arches: Shared characteristics among Dlx bigene clusters and evolution.

Development, growth & differentiation, 62(5):355-362.

The mammalian Dlx genes encode homeobox-type transcription factors and are physically organized as convergent bigene clusters. The paired Dlx genes share tissue specificity in the expression profile. Genetic regulatory mechanisms, such as intergenic enhancer sharing between paired Dlx genes, have been proposed to explain this conservation of bigene structure. All mammalian Dlx genes have expression and function in developing craniofacial structures, especially in the first and second pharyngeal arches (branchial arches). Each Dlx cluster (Dlx1/2, Dlx3/4, and Dlx5/6) has overlapping, nested expression in the branchial arches which is called the "Dlx code" and plays a key role in organizing craniofacial structure and evolution. Here we summarize cis-regulatory studies on branchial arch expression of the three Dlx bigene clusters and show some shared characteristics among the clusters, including cis-regulatory motifs, TAD (Topologically Associating Domain) boundaries, CTCF loops, and distal enhancer landscapes, together with a molecular condensate model for activation of the Dlx bigene cluster.

RevDate: 2020-08-24
CmpDate: 2020-08-24

Bian Q, Anderson EC, Yang Q, et al (2020)

Histone H3K9 methylation promotes formation of genome compartments in Caenorhabditis elegans via chromosome compaction and perinuclear anchoring.

Proceedings of the National Academy of Sciences of the United States of America, 117(21):11459-11470.

Genomic regions preferentially associate with regions of similar transcriptional activity, partitioning genomes into active and inactive compartments within the nucleus. Here we explore mechanisms controlling genome compartment organization in Caenorhabditis elegans and investigate roles for compartments in regulating gene expression. Distal arms of C. elegans chromosomes, which are enriched for heterochromatic histone modifications H3K9me1/me2/me3, interact with each other both in cis and in trans, while interacting less frequently with central regions, leading to genome compartmentalization. Arms are anchored to the nuclear periphery via the nuclear envelope protein CEC-4, which binds to H3K9me. By performing genome-wide chromosome conformation capture experiments (Hi-C), we showed that eliminating H3K9me1/me2/me3 through mutations in the methyltransferase genes met-2 and set-25 significantly impaired formation of inactive Arm and active Center compartments. cec-4 mutations also impaired compartmentalization, but to a lesser extent. We found that H3K9me promotes compartmentalization through two distinct mechanisms: Perinuclear anchoring of chromosome arms via CEC-4 to promote their cis association, and an anchoring-independent mechanism that compacts individual chromosome arms. In both met-2 set-25 and cec-4 mutants, no dramatic changes in gene expression were found for genes that switched compartments or for genes that remained in their original compartment, suggesting that compartment strength does not dictate gene-expression levels. Furthermore, H3K9me, but not perinuclear anchoring, also contributes to formation of another prominent feature of chromosome organization, megabase-scale topologically associating domains on X established by the dosage compensation condensin complex. Our results demonstrate that H3K9me plays crucial roles in regulating genome organization at multiple levels.

RevDate: 2020-09-24

Yang M, Safavi S, Woodward EL, et al (2020)

13q12.2 deletions in acute lymphoblastic leukemia lead to upregulation of FLT3 through enhancer hijacking.

Blood, 136(8):946-956.

Mutations in the FMS-like tyrosine kinase 3 (FLT3) gene in 13q12.2 are among the most common driver events in acute leukemia, leading to increased cell proliferation and survival through activation of the phosphatidylinositol 3-kinase/AKT-, RAS/MAPK-, and STAT5-signaling pathways. In this study, we examine the pathogenetic impact of somatic hemizygous 13q12.2 microdeletions in B-cell precursor (BCP) acute lymphoblastic leukemia (ALL) using 5 different patient cohorts (in total including 1418 cases). The 13q12.2 deletions occur immediately 5' of FLT3 and involve the PAN3 locus. By detailed analysis of the 13q12.2 segment, we show that the deletions lead to loss of a topologically associating domain border and an enhancer of FLT3. This results in increased cis interactions between the FLT3 promoter and another enhancer located distally to the deletion breakpoints, with subsequent allele-specific upregulation of FLT3 expression, expected to lead to ligand-independent activation of the receptor and downstream signaling. The 13q12.2 deletions are highly enriched in the high-hyperdiploid BCP ALL subtype (frequency 3.9% vs 0.5% in other BCP ALL) and in cases that subsequently relapsed. Taken together, our study describes a novel mechanism of FLT3 involvement in leukemogenesis by upregulation via chromatin remodeling and enhancer hijacking. These data further emphasize the role of FLT3 as a driver gene in BCP ALL.

RevDate: 2020-09-28

Pérez-Rico YA, Barillot E, A Shkumatava (2020)

Demarcation of Topologically Associating Domains Is Uncoupled from Enriched CTCF Binding in Developing Zebrafish.

iScience, 23(5):101046.

CCCTC-binding factor (CTCF) is a conserved architectural protein that plays crucial roles in gene regulation and three-dimensional (3D) chromatin organization. To better understand mechanisms and evolution of vertebrate genome organization, we analyzed genome occupancy of CTCF in zebrafish utilizing an endogenously epitope-tagged CTCF knock-in allele. Zebrafish CTCF shares similar facets with its mammalian counterparts, including binding to enhancers, active promoters and repeat elements, and bipartite sequence motifs of its binding sites. However, we found that in vivo CTCF binding is not enriched at boundaries of topologically associating domains (TADs) in developing zebrafish, whereas TAD demarcation by chromatin marks did not differ from mammals. Our data suggest that general mechanisms underlying 3D chromatin organization, and in particular the involvement of CTCF in this process, differ between distant vertebrate species.

RevDate: 2020-06-05

Zhang Z, Wang Q, Liu Y, et al (2020)

Massive reorganization of the genome during primary monocyte differentiation into macrophage.

Acta biochimica et biophysica Sinica, 52(5):546-553.

Monocyte-to-macrophage trans-differentiation has long been studied to better understand this immunological response and aspects of developmental processes more generally. A key question is the nature of the corresponding changes in chromatin conformation and its relationship to the transcriptome during this process. This question is especially intriguing since this trans-differentiation is not associated with progression through mitosis, often considered a necessary step for gross changes in chromosomal structure. Here, we characterized the transcriptional and genomic structural changes during macrophage development of primary human monocytes using RNA-seq and in situ Hi-C. We found that, during this transition, the genome architecture undergoes a massive remodeling to a degree not observed before between structured genomes, with changes in ~90% of the topologically associating domains (TADs). These changes in the TADs are associated with changed expression of immunological genes. These structural changes, however, differ extensively from those described recently in a study of the leukemia cell line, THP-1. Furthermore, up-regulation of the AP-1 family of genes that effected functionally important changes in the genomic structure during the differentiation of the THP-1 cells was not corroborated with the primary cells. Taken together, our results provide a comprehensive characterization of the changes in genomic structure during the monocyte-to-macrophage transition, establish a framework for the elucidation of processes underlying differentiation without proliferation, and demonstrate the importance of verifying with primary cells the mechanisms discovered with cultured cells.

RevDate: 2020-09-28

Luo Z, Wang X, Jiang H, et al (2020)

Reorganized 3D Genome Structures Support Transcriptional Regulation in Mouse Spermatogenesis.

iScience, 23(4):101034.

Three-dimensional chromatin structures undergo dynamic reorganization during mammalian spermatogenesis; however, their impacts on gene regulation remain unclear. Here, we focused on understanding the structure-function regulation of meiotic chromosomes by Hi-C and other omics techniques in mouse spermatogenesis across five stages. Beyond confirming recent reports regarding changes in compartmentalization and reorganization of topologically associating domains (TADs), we further demonstrated that chromatin loops are present prior to and after, but not at, the pachytene stage. By integrating Hi-C and RNA-seq data, we showed that the switching of A/B compartments between spermatogenic stages is tightly associated with meiosis-specific mRNAs and piRNAs expression. Moreover, our ATAC-seq data indicated that chromatin accessibility per se is not responsible for the TAD and loop diminishment at pachytene. Additionally, our ChIP-seq data demonstrated that CTCF and cohesin remain bound at TAD boundary regions throughout meiosis, suggesting that dynamic reorganization of TADs does not require CTCF and cohesin clearance.

RevDate: 2020-09-08
CmpDate: 2020-09-08

Kantidze OL, SV Razin (2020)

Weak interactions in higher-order chromatin organization.

Nucleic acids research, 48(9):4614-4626.

The detailed principles of the hierarchical folding of eukaryotic chromosomes have been revealed during the last two decades. Along with structures composing three-dimensional (3D) genome organization (chromatin compartments, topologically associating domains, chromatin loops, etc.), the molecular mechanisms that are involved in their establishment and maintenance have been characterized. Generally, protein-protein and protein-DNA interactions underlie the spatial genome organization in eukaryotes. However, it is becoming increasingly evident that weak interactions, which exist in biological systems, also contribute to the 3D genome. Here, we provide a snapshot of our current understanding of the role of the weak interactions in the establishment and maintenance of the 3D genome organization. We discuss how weak biological forces, such as entropic forces operating in crowded solutions, electrostatic interactions of the biomolecules, liquid-liquid phase separation, DNA supercoiling, and RNA environment participate in chromosome segregation into structural and functional units and drive intranuclear functional compartmentalization.

RevDate: 2020-04-30

Amândio AR, Lopez-Delisle L, Bolt CC, et al (2020)

A complex regulatory landscape involved in the development of mammalian external genitals.

eLife, 9:.

Developmental genes are often controlled by large regulatory landscapes matching topologically associating domains (TADs). In various contexts, the associated chromatin backbone is modified by specific enhancer-enhancer and enhancer-promoter interactions. We used a TAD flanking the mouse HoxD cluster to study how these regulatory architectures are formed and deconstructed once their function achieved. We describe this TAD as a functional unit, with several regulatory sequences acting together to elicit a transcriptional response. With one exception, deletion of these sequences didn't modify the transcriptional outcome, a result at odds with a conventional view of enhancer function. The deletion and inversion of a CTCF site located near these regulatory sequences did not affect transcription of the target gene. Slight modifications were nevertheless observed, in agreement with the loop extrusion model. We discuss these unexpected results considering both conventional and alternative explanations relying on the accumulation of poorly specific factors within the TAD backbone.

RevDate: 2020-07-21
CmpDate: 2020-07-21

Chen M, Zhu Q, Li C, et al (2020)

Chromatin architecture reorganization in murine somatic cell nuclear transfer embryos.

Nature communications, 11(1):1813.

The oocyte cytoplasm can reprogram the somatic cell nucleus into a totipotent state, but with low efficiency. The spatiotemporal chromatin organization of somatic cell nuclear transfer (SCNT) embryos remains elusive. Here, we examine higher order chromatin structures of mouse SCNT embryos using a low-input Hi-C method. We find that donor cell chromatin transforms to the metaphase state rapidly after SCNT along with the dissolution of typical 3D chromatin structure. Intriguingly, the genome undergoes a mitotic metaphase-like to meiosis metaphase II-like transition following activation. Subsequently, weak chromatin compartments and topologically associating domains (TADs) emerge following metaphase exit. TADs are further removed until the 2-cell stage before being progressively reestablished. Obvious defects including stronger TAD boundaries, aberrant super-enhancer and promoter interactions are found in SCNT embryos. These defects are partially caused by inherited H3K9me3, and can be rescued by Kdm4d overexpression. These observations provide insight into chromatin architecture reorganization during SCNT embryo development.

RevDate: 2020-07-07

Wang G, Meng Q, Xia B, et al (2020)

TADsplimer reveals splits and mergers of topologically associating domains for epigenetic regulation of transcription.

Genome biology, 21(1):84.

We present TADsplimer, the first computational tool to systematically detect topologically associating domain (TAD) splits and mergers across the genome between Hi-C samples. TADsplimer recaptures splits and mergers of TADs with high accuracy in simulation analyses and defines hundreds of TAD splits and mergers between pairs of different cell types, such as endothelial cells and fibroblasts. Our work reveals a key role for TAD remodeling in epigenetic regulation of transcription and delivers the first tool for the community to perform dynamic analysis of TAD splits and mergers in numerous biological and disease models.

RevDate: 2020-06-17

Pontvianne F, S Grob (2020)

Three-dimensional nuclear organization in Arabidopsis thaliana.

Journal of plant research, 133(4):479-488.

In recent years, the study of plant three-dimensional nuclear architecture received increasing attention. Enabled by technological advances, our knowledge on nuclear architecture has greatly increased and we can now access large data sets describing its manifold aspects. The principles of nuclear organization in plants do not significantly differ from those in animals. Plant nuclear organization comprises various scales, ranging from gene loops to topologically associating domains to nuclear compartmentalization. However, whether plant three-dimensional chromosomal features also exert similar functions as in animals is less clear. This review discusses recent advances in the fields of three-dimensional chromosome folding and nuclear compartmentalization and describes a novel silencing mechanism, which is closely linked to nuclear architecture.

RevDate: 2020-08-28
CmpDate: 2020-08-28

Krietenstein N, Abraham S, Venev SV, et al (2020)

Ultrastructural Details of Mammalian Chromosome Architecture.

Molecular cell, 78(3):554-565.e7.

Over the past decade, 3C-related methods have provided remarkable insights into chromosome folding in vivo. To overcome the limited resolution of prior studies, we extend a recently developed Hi-C variant, Micro-C, to map chromosome architecture at nucleosome resolution in human ESCs and fibroblasts. Micro-C robustly captures known features of chromosome folding including compartment organization, topologically associating domains, and interactions between CTCF binding sites. In addition, Micro-C provides a detailed map of nucleosome positions and localizes contact domain boundaries with nucleosomal precision. Compared to Hi-C, Micro-C exhibits an order of magnitude greater dynamic range, allowing the identification of ∼20,000 additional loops in each cell type. Many newly identified peaks are localized along extrusion stripes and form transitive grids, consistent with their anchors being pause sites impeding cohesin-dependent loop extrusion. Our analyses comprise the highest-resolution maps of chromosome folding in human cells to date, providing a valuable resource for studies of chromosome organization.

RevDate: 2020-08-28
CmpDate: 2020-08-28

Hsieh TS, Cattoglio C, Slobodyanyuk E, et al (2020)

Resolving the 3D Landscape of Transcription-Linked Mammalian Chromatin Folding.

Molecular cell, 78(3):539-553.e8.

Whereas folding of genomes at the large scale of epigenomic compartments and topologically associating domains (TADs) is now relatively well understood, how chromatin is folded at finer scales remains largely unexplored in mammals. Here, we overcome some limitations of conventional 3C-based methods by using high-resolution Micro-C to probe links between 3D genome organization and transcriptional regulation in mouse stem cells. Combinatorial binding of transcription factors, cofactors, and chromatin modifiers spatially segregates TAD regions into various finer-scale structures with distinct regulatory features including stripes, dots, and domains linking promoters-to-promoters (P-P) or enhancers-to-promoters (E-P) and bundle contacts between Polycomb regions. E-P stripes extending from the edge of domains predominantly link co-expressed loci, often in the absence of CTCF and cohesin occupancy. Acute inhibition of transcription disrupts these gene-related folding features without altering higher-order chromatin structures. Our study uncovers previously obscured finer-scale genome organization, establishing functional links between chromatin folding and gene regulation.

RevDate: 2020-09-23
CmpDate: 2020-06-26

Kloetgen A, Thandapani P, Ntziachristos P, et al (2020)

Three-dimensional chromatin landscapes in T cell acute lymphoblastic leukemia.

Nature genetics, 52(4):388-400.

Differences in three-dimensional (3D) chromatin architecture can influence the integrity of topologically associating domains (TADs) and rewire specific enhancer-promoter interactions, impacting gene expression and leading to human disease. Here we investigate the 3D chromatin architecture in T cell acute lymphoblastic leukemia (T-ALL) by using primary human leukemia specimens and examine the dynamic responses of this architecture to pharmacological agents. Systematic integration of matched in situ Hi-C, RNA-seq and CTCF ChIP-seq datasets revealed widespread differences in intra-TAD chromatin interactions and TAD boundary insulation in T-ALL. Our studies identify and focus on a TAD 'fusion' event associated with absence of CTCF-mediated insulation, enabling direct interactions between the MYC promoter and a distal super-enhancer. Moreover, our data also demonstrate that small-molecule inhibitors targeting either oncogenic signal transduction or epigenetic regulation can alter specific 3D interactions found in leukemia. Overall, our study highlights the impact, complexity and dynamic nature of 3D chromatin architecture in human acute leukemia.

RevDate: 2020-09-21

Ibrahim DM, S Mundlos (2020)

The role of 3D chromatin domains in gene regulation: a multi-facetted view on genome organization.

Current opinion in genetics & development, 61:1-8.

The causal relationship between 3D chromatin domains and gene regulation has been of considerable debate in recent years. Initial Hi-C studies profiling the 3D chromatin structure of the genome described evolutionarily conserved Topologically Associating Domains (TADs) that correlated with gene expression. Subsequent evidence from mouse models and human disease directly linked TADs to gene regulation. However, a number of focused genetic and genome-wide studies questioned the relevance of 3D chromatin domains for orchestrating gene expression, ultimately yielding a more multi-layered view of 3D chromatin structure and gene regulation. We review the evidence for and against the importance of 3D chromatin structure for gene regulation and argue for a more comprehensive classification of regulatory chromatin domains that integrates 3D chromatin structure with genomic, functional, and evolutionary conservation.

RevDate: 2020-09-19
CmpDate: 2020-07-16

Carstens S, Nilges M, M Habeck (2020)

Bayesian inference of chromatin structure ensembles from population-averaged contact data.

Proceedings of the National Academy of Sciences of the United States of America, 117(14):7824-7830.

Mounting experimental evidence suggests a role for the spatial organization of chromatin in crucial processes of the cell nucleus such as transcription regulation. Chromosome conformation capture techniques allow us to characterize chromatin structure by mapping contacts between chromosomal loci on a genome-wide scale. The most widespread modality is to measure contact frequencies averaged over a population of cells. Single-cell variants exist, but suffer from low contact numbers and have not yet gained the same resolution as population methods. While intriguing biological insights have already been garnered from ensemble-averaged data, information about three-dimensional (3D) genome organization in the underlying individual cells remains largely obscured because the contact maps show only an average over a huge population of cells. Moreover, computational methods for structure modeling of chromatin have mostly focused on fitting a single consensus structure, thereby ignoring any cell-to-cell variability in the model itself. Here, we propose a fully Bayesian method to infer ensembles of chromatin structures and to determine the optimal number of states in a principled, objective way. We illustrate our approach on simulated data and compute multistate models of chromatin from chromosome conformation capture carbon copy (5C) data. Comparison with independent data suggests that the inferred ensembles represent the underlying sample population faithfully. Harnessing the rich information contained in multistate models, we investigate cell-to-cell variability of chromatin organization into topologically associating domains, thus highlighting the ability of our approach to deliver insights into chromatin organization of great biological relevance.

RevDate: 2020-10-11

Shinkai S, Sugawara T, Miura H, et al (2020)

Microrheology for Hi-C Data Reveals the Spectrum of the Dynamic 3D Genome Organization.

Biophysical journal, 118(9):2220-2228.

The one-dimensional information of genomic DNA is hierarchically packed inside the eukaryotic cell nucleus and organized in a three-dimensional (3D) space. Genome-wide chromosome conformation capture (Hi-C) methods have uncovered the 3D genome organization and revealed multiscale chromatin domains of compartments and topologically associating domains (TADs). Moreover, single-nucleosome live-cell imaging experiments have revealed the dynamic organization of chromatin domains caused by stochastic thermal fluctuations. However, the mechanism underlying the dynamic regulation of such hierarchical and structural chromatin units within the microscale thermal medium remains unclear. Microrheology is a way to measure dynamic viscoelastic properties coupling between thermal microenvironment and mechanical response. Here, we propose a new, to our knowledge, microrheology for Hi-C data to analyze the dynamic compliance property as a measure of rigidness and flexibility of genomic regions along with the time evolution. Our method allows the conversion of an Hi-C matrix into the spectrum of the dynamic rheological property along the genomic coordinate of a single chromosome. To demonstrate the power of the technique, we analyzed Hi-C data during the neural differentiation of mouse embryonic stem cells. We found that TAD boundaries behave as more rigid nodes than the intra-TAD regions. The spectrum clearly shows the dynamic viscoelasticity of chromatin domain formation at different timescales. Furthermore, we characterized the appearance of synchronous and liquid-like intercompartment interactions in differentiated cells. Together, our microrheology data derived from Hi-C data provide physical insights into the dynamics of the 3D genome organization.

RevDate: 2020-09-01

Luo Z, Hu T, Jiang H, et al (2020)

Rearrangement of macronucleus chromosomes correspond to TAD-like structures of micronucleus chromosomes in Tetrahymena thermophila.

Genome research, 30(3):406-414.

The somatic macronucleus (MAC) and germline micronucleus (MIC) of Tetrahymena thermophila differ in chromosome numbers, sizes, functions, transcriptional activities, and cohesin complex location. However, the higher-order chromatin organization in T. thermophila is still largely unknown. Here, we explored the higher-order chromatin organization in the two distinct nuclei of T. thermophila using the Hi-C and HiChIP methods. We found that the meiotic crescent MIC has a specific chromosome interaction pattern, with all the telomeres or centromeres on the five MIC chromosomes clustering together, respectively, which is also helpful to identify the midpoints of centromeres in the MIC. We revealed that the MAC chromosomes lack A/B compartments, topologically associating domains (TADs), and chromatin loops. The MIC chromosomes have TAD-like structures but not A/B compartments and chromatin loops. The boundaries of the TAD-like structures in the MIC are highly consistent with the chromatin breakage sequence (CBS) sites, suggesting that each TAD-like structure of the MIC chromosomes develops into one MAC chromosome during MAC development, which provides a mechanism of the formation of MAC chromosomes during conjugation. Overall, we demonstrated the distinct higher-order chromatin organization in the two nuclei of the T. thermophila and suggest that the higher-order chromatin structures may play important roles during the development of the MAC chromosomes.

RevDate: 2020-10-05

Santana JF, Parida M, Long A, et al (2020)

The Dm-Myb Oncoprotein Contributes to Insulator Function and Stabilizes Repressive H3K27me3 PcG Domains.

Cell reports, 30(10):3218-3228.e5.

Drosophila Myb (Dm-Myb) encodes a protein that plays a key role in regulation of mitotic phase genes. Here, we further refine its role in the context of a developing tissue as a potentiator of gene expression required for proper RNA polymerase II (RNA Pol II) function and efficient H3K4 methylation at promoters. In contrast to its role in gene activation, Myb is also required for repression of many genes, although no specific mechanism for this role has been proposed. We now reveal a critical role for Myb in contributing to insulator function, in part by promoting binding of insulator proteins BEAF-32 and CP190 and stabilizing H3K27me3 Polycomb-group (PcG) domains. In the absence of Myb, H3K27me3 is markedly reduced throughout the genome, leading to H3K4me3 spreading and gene derepression. Finally, Myb is enriched at boundaries that demarcate chromatin environments, including chromatin loop anchors. These results reveal functions of Myb that extend beyond transcriptional regulation.

RevDate: 2020-09-28

Van der Veen DR, Laing EE, Bae SE, et al (2020)

A Topological Cluster of Differentially Regulated Genes in Mice Lacking PER3.

Frontiers in molecular neuroscience, 13:15.

Polymorphisms in the human circadian clock gene PERIOD3 (PER3) are associated with a wide variety of phenotypes such as diurnal preference, delayed sleep phase disorder, sleep homeostasis, cognitive performance, bipolar disorder, type 2 diabetes, cardiac regulation, cancer, light sensitivity, hormone and cytokine secretion, and addiction. However, the molecular mechanisms underlying these phenotypic associations remain unknown. Per3 knockout mice (Per3-/-) have phenotypes related to activity, sleep homeostasis, anhedonia, metabolism, and behavioral responses to light. Using a protocol that induces behavioral differences in response to light in wild type and Per3-/- mice, we compared genome-wide expression in the eye and hypothalamus in the two genotypes. Differentially expressed transcripts were related to inflammation, taste, olfactory and melatonin receptors, lipid metabolism, cell cycle, ubiquitination, and hormones, as well as receptors and channels related to sleep regulation. Differentially expressed transcripts in both tissues co-localized with Per3 on an ∼8Mbp region of distal chromosome 4. The most down-regulated transcript is Prdm16, which is involved in adipocyte differentiation and may mediate altered body mass accumulation in Per3-/- mice. eQTL analysis with BXD mouse strains showed that the expression of some of these transcripts and also others co-localized at distal chromosome 4, is correlated with brain tissue expression levels of Per3 with a highly significant linkage to genetic variation in that region. These data identify a cluster of transcripts on mouse distal chromosome 4 that are co-regulated with Per3 and whose expression levels correlate with those of Per3. This locus lies within a topologically associating domain island that contains many genes with functional links to several of the diverse non-circadian phenotypes associated with polymorphisms in human PER3.

RevDate: 2020-07-17
CmpDate: 2020-07-17

Ji L, Huo X, Zhang Y, et al (2020)

TOPORS, a tumor suppressor protein, contributes to the maintenance of higher-order chromatin architecture.

Biochimica et biophysica acta. Gene regulatory mechanisms, 1863(5):194518.

In the nucleus, chromosomes are hierarchically folded into active (A) and inactive (B) compartments composed of topologically associating domains (TADs). Genomic regions interact with nuclear lamina, termed lamina-associated domains (LADs). However, the molecular mechanisms underlying these 3D chromatin architectures remain incompletely understood. Here, we investigated the role of a potential tumor suppressor, TOP1 Binding Arginine/Serine Rich Protein (TOPORS), in genome organization. In mouse hepatocytes, chromatin interactions between A and B compartments increase and compartmentalization strength is reduced significantly upon Topors knockdown. Correspondingly, strength of TAD boundaries located at A/B borders is weakened. In the absence of TOPORS, chromatin-lamina interactions decrease and the coverage of LADs reduces from 53.31% to 46.52%. Interestingly, these changes in 3D genome are associated with PML nuclear bodies and PML-associated domains (PADs). Moreover, chromatin accessibility is altered predominantly at intergenic regions upon Topors knockdown, including a subset of enhancers. These alterations of chromatin are concordant with transcriptome changes, which are associated with carcinogenesis. Collectively, our findings demonstrate that TOPORS functions as a regulator in chromatin structure, providing novel insight into the architectural roles of tumor suppressors in higher-order genome organization.

RevDate: 2020-09-28

Sjakste T, Leonova E, Petrovs R, et al (2020)

Tight DNA-protein complexes isolated from barley seedlings are rich in potential guanine quadruplex sequences.

PeerJ, 8:e8569.

Background: The concept of chromatin domains attached to the nuclear matrix is being revisited, with nucleus described as a set of topologically associating domains. The significance of the tightly bound to DNA proteins (TBP), a protein group that remains attached to DNA after its deproteinization should be also revisited, as the existence of these interactions is in good agreement with the concept of the topologically associating domain. The work aimed to characterize the DNA component of TBP isolated from barley seedlings.

Methods: The tight DNA-protein complexes from the first leaves, coleoptiles, and roots of barley seedlings were isolated by purification with chromatography on nitrocellulose or exhaustive digestion of DNA with DNase I. Cloning and transformation were performed using pMOSBBlue Blunt Ended Cloning Kit. Inserts were amplified by PCR, and sequencing was performed on the MegaBace 1000 Sequencing System. The BLAST search was performed using sequence databases at NCBI, CR-EST, and TREP and Ensembl Plants databases. Comparison to MAR/SAR sequences was performed using http://smartdb.bioinf.med.uni-goettingen.de/cgi-bin/SMARtDB/smar.cgi database. The prediction of G quadruplexes (GQ) was performed with the aid of R-studio library pqsfinder. CD spectra were recorded on a Chirascan CS/3D spectrometer.

Results: Although the barley genome is AT-rich (43% of GC pairs), most DNA fragments associated with TBP were GC-rich (up to 70% in some fractions). Both fractionation procedures yielded a high proportion of CT-motif sequences presented predominantly by the 16-bp CC(TCTCCC)2 TC fragment present in clones derived from the TBP-bound DNA and absent in free DNA. BLAST analysis revealed alignment with different barley repeats. Some clones, however, aligned with both nuclear and chloroplast structural genes. Alignments with MAR/SAR motifs were very few. The analysis produced by the pqsfinder program revealed numerous potential quadruplex-forming sites in the TBP-bound sequences. A set of oligonucleotides containing sites of possible GQs were designed and ordered. Three of them represented the minus strand of the CT-repeat. Two were derived from sequences of two clones of nitrocellulose retained fraction from leaves and contained GC-rich motifs different from the CT motif. Circular dichroism spectroscopy revealed profound changes in spectra when oligonucleotides were incubated with 100 mM KCl. There was either an increase of positive band in the area of 260 nm or the formation of a positive band at 290 nm. In the former case, changes are typical for parallel G-quadruplexes and, in the latter, 3 + 1 structures.

Discussion: The G-quadruplexes anchor proteins are probably involved in the maintenance of the topologically associated domain structure.

RevDate: 2020-08-13
CmpDate: 2020-08-13

Yokoshi M, Segawa K, T Fukaya (2020)

Visualizing the Role of Boundary Elements in Enhancer-Promoter Communication.

Molecular cell, 78(2):224-235.e5.

Formation of self-associating loop domains is a fundamental organizational feature of metazoan genomes. Here, we employed quantitative live-imaging methods to visualize impacts of higher-order chromosome topology on enhancer-promoter communication in developing Drosophila embryos. Evidence is provided that distal enhancers effectively produce transcriptional bursting from target promoters over distances when they are flanked with boundary elements. Importantly, neither inversion nor deletion of a boundary element abrogates this "enhancer-assisting activity," suggesting that they can facilitate intra-domain enhancer-promoter interaction and production of transcriptional bursting independently of topologically associating domain (TAD) formation. In contrast, domain-skipping activity of distal enhancers was lost after disruption of topological domains. This observation raises a possibility that intra-domain and inter-domain enhancer-promoter interactions are differentially regulated by chromosome topology.

RevDate: 2020-10-02

Lazaris C, Aifantis I, A Tsirigos (2020)

On Epigenetic Plasticity and Genome Topology.

Trends in cancer, 6(3):177-180.

Mounting evidence links genetic lesions with genome topology alterations and aberrant gene activation. However, the role of epigenetic plasticity remains elusive. Emerging studies implicate DNA methylation, transcriptional elongation, long noncoding RNAs (lncRNAs), and CCCTC-binding factor (CTCF)-RNA interactions, but systematic approaches are needed to fully decipher the role of epigenetic plasticity in genome integrity and function.

RevDate: 2020-07-11
CmpDate: 2020-05-22

Li Y, Liao Z, Luo H, et al (2020)

Alteration of CTCF-associated chromatin neighborhood inhibits TAL1-driven oncogenic transcription program and leukemogenesis.

Nucleic acids research, 48(6):3119-3133.

Aberrant activation of the TAL1 is associated with up to 60% of T-ALL cases and is involved in CTCF-mediated genome organization within the TAL1 locus, suggesting that CTCF boundary plays a pathogenic role in T-ALL. Here, we show that -31-Kb CTCF binding site (-31CBS) serves as chromatin boundary that defines topologically associating domain (TAD) and enhancer/promoter interaction required for TAL1 activation. Deleted or inverted -31CBS impairs TAL1 expression in a context-dependent manner. Deletion of -31CBS reduces chromatin accessibility and blocks long-range interaction between the +51 erythroid enhancer and TAL1 promoter-1 leading to inhibition of TAL1 expression in erythroid cells, but not T-ALL cells. However, in TAL1-expressing T-ALL cells, the leukemia-prone TAL1 promoter-IV specifically interacts with the +19 stem cell enhancer located 19 Kb downstream of TAL1 and this interaction is disrupted by the -31CBS inversion in T-ALL cells. Inversion of -31CBS in Jurkat cells alters chromatin accessibility, histone modifications and CTCF-mediated TAD leading to inhibition of TAL1 expression and TAL1-driven leukemogenesis. Thus, our data reveal that -31CBS acts as critical regulator to define +19-enhancer and the leukemic prone promoter IV interaction for TAL1 activation in T-ALL. Manipulation of CTCF boundary can alter TAL1 TAD and oncogenic transcription networks in leukemogenesis.

RevDate: 2020-07-06
CmpDate: 2020-07-06

Soler-Vila P, Cuscó P, Farabella I, et al (2020)

Hierarchical chromatin organization detected by TADpole.

Nucleic acids research, 48(7):e39.

The rapid development of Chromosome Conformation Capture (3C-based techniques), as well as imaging together with bioinformatics analyses, has been fundamental for unveiling that chromosomes are organized into the so-called topologically associating domains or TADs. While TADs appear as nested patterns in the 3C-based interaction matrices, the vast majority of available TAD callers are based on the hypothesis that TADs are individual and unrelated chromatin structures. Here we introduce TADpole, a computational tool designed to identify and analyze the entire hierarchy of TADs in intra-chromosomal interaction matrices. TADpole combines principal component analysis and constrained hierarchical clustering to provide a set of significant hierarchical chromatin levels in a genomic region of interest. TADpole is robust to data resolution, normalization strategy and sequencing depth. Domain borders defined by TADpole are enriched in main architectural proteins (CTCF and cohesin complex subunits) and in the histone mark H3K4me3, while their domain bodies, depending on their activation-state, are enriched in either H3K36me3 or H3K27me3, highlighting that TADpole is able to distinguish functional TAD units. Additionally, we demonstrate that TADpole's hierarchical annotation, together with the new DiffT score, allows for detecting significant topological differences on Capture Hi-C maps between wild-type and genetically engineered mouse.

RevDate: 2020-06-01
CmpDate: 2020-06-01

Arzate-Mejía RG, Josué Cerecedo-Castillo A, Guerrero G, et al (2020)

In situ dissection of domain boundaries affect genome topology and gene transcription in Drosophila.

Nature communications, 11(1):894.

Chromosomes are organized into high-frequency chromatin interaction domains called topologically associating domains (TADs), which are separated from each other by domain boundaries. The molecular mechanisms responsible for TAD formation are not yet fully understood. In Drosophila, it has been proposed that transcription is fundamental for TAD organization while the participation of genetic sequences bound by architectural proteins (APs) remains controversial. Here, we investigate the contribution of domain boundaries to TAD organization and the regulation of gene expression at the Notch gene locus in Drosophila. We find that deletion of domain boundaries results in TAD fusion and long-range topological defects that are accompanied by loss of APs and RNA Pol II chromatin binding as well as defects in transcription. Together, our results provide compelling evidence of the contribution of discrete genetic sequences bound by APs and RNA Pol II in the partition of the genome into TADs and in the regulation of gene expression in Drosophila.

RevDate: 2020-07-20

Ibrahim DM, S Mundlos (2020)

Three-dimensional chromatin in disease: What holds us together and what drives us apart?.

Current opinion in cell biology, 64:1-9.

Recent advances in understanding spatial genome organization inside the nucleus have shown that chromatin is compartmentalized into megabase-scale units known as topologically associating domains (TADs). In further studies, TADs were linked to differing transcriptional activity, suggesting that they might provide a scaffold for gene regulation by promoting enhancer-promoter interaction and by insulating regulatory activities. One strong argument for this hypothesis was provided by the effects of disease-causing structural variations in congenital disease and cancer. By rearranging TADs, these mutations result in a rewiring of enhancer-promoter contacts, consecutive gene misexpression, and ultimately disease. However, not all rearrangements are equally effective in creating these effects. Here, we review several recent studies aiming to understand the mechanisms by which disease-causing mutations achieve gene misregulation. We will discuss which regulatory effects are to be expected by different disease mutations and how this new knowledge can be used for diagnostics in the clinic.

RevDate: 2020-05-14
CmpDate: 2020-04-14

Akdemir KC, Le VT, Chandran S, et al (2020)

Disruption of chromatin folding domains by somatic genomic rearrangements in human cancer.

Nature genetics, 52(3):294-305.

Chromatin is folded into successive layers to organize linear DNA. Genes within the same topologically associating domains (TADs) demonstrate similar expression and histone-modification profiles, and boundaries separating different domains have important roles in reinforcing the stability of these features. Indeed, domain disruptions in human cancers can lead to misregulation of gene expression. However, the frequency of domain disruptions in human cancers remains unclear. Here, as part of the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA), which aggregated whole-genome sequencing data from 2,658 cancers across 38 tumor types, we analyzed 288,457 somatic structural variations (SVs) to understand the distributions and effects of SVs across TADs. Notably, SVs can lead to the fusion of discrete TADs, and complex rearrangements markedly change chromatin folding maps in the cancer genomes. Notably, only 14% of the boundary deletions resulted in a change in expression in nearby genes of more than twofold.

RevDate: 2020-08-03
CmpDate: 2020-08-03

Bolt CC, D Duboule (2020)

The regulatory landscapes of developmental genes.

Development (Cambridge, England), 147(3):.

Regulatory landscapes have been defined in vertebrates as large DNA segments containing diverse enhancer sequences that produce coherent gene transcription. These genomic platforms integrate multiple cellular signals and hence can trigger pleiotropic expression of developmental genes. Identifying and evaluating how these chromatin regions operate may be difficult as the underlying regulatory mechanisms can be as unique as the genes they control. In this brief article and accompanying poster, we discuss some of the ways in which regulatory landscapes operate, illustrating these mechanisms using genes important for vertebrate development as examples. We also highlight some of the techniques available to researchers for analysing regulatory landscapes.

RevDate: 2020-05-20
CmpDate: 2020-05-20

Kumar V, Leclerc S, Y Taniguchi (2020)

BHi-Cect: a top-down algorithm for identifying the multi-scale hierarchical structure of chromosomes.

Nucleic acids research, 48(5):e26.

High-throughput chromosome conformation capture (Hi-C) technology enables the investigation of genome-wide interactions among chromosome loci. Current algorithms focus on topologically associating domains (TADs), that are contiguous clusters along the genome coordinate, to describe the hierarchical structure of chromosomes. However, high resolution Hi-C displays a variety of interaction patterns beyond what current TAD detection methods can capture. Here, we present BHi-Cect, a novel top-down algorithm that finds clusters by considering every locus with no assumption of genomic contiguity using spectral clustering. Our results reveal that the hierarchical structure of chromosome is organized as 'enclaves', which are complex interwoven clusters at both local and global scales. We show that the nesting of local clusters within global clusters characterizing enclaves, is associated with the epigenomic activity found on the underlying DNA. Furthermore, we show that the hierarchical nesting that links different enclaves integrates their respective function. BHi-Cect provides means to uncover the general principles guiding chromatin architecture.

RevDate: 2020-09-03

Brackley CA, D Marenduzzo (2020)

Bridging-induced microphase separation: photobleaching experiments, chromatin domains and the need for active reactions.

Briefings in functional genomics, 19(2):111-118.

We review the mechanism and consequences of the 'bridging-induced attraction', a generic biophysical principle that underpins some existing models for chromosome organization in 3D. This attraction, which was revealed in polymer physics-inspired computer simulations, is a generic clustering tendency arising in multivalent chromatin-binding proteins, and it provides an explanation for the biogenesis of nuclear bodies and transcription factories via microphase separation. Including post-translational modification reactions involving these multivalent proteins can account for the fast dynamics of the ensuing clusters, as is observed via microscopy and photobleaching experiments. The clusters found in simulations also give rise to chromatin domains that conform well with the observation of A/B compartments in HiC experiments.

RevDate: 2020-07-30

Rhodes JDP, Feldmann A, Hernández-Rodríguez B, et al (2020)

Cohesin Disrupts Polycomb-Dependent Chromosome Interactions in Embryonic Stem Cells.

Cell reports, 30(3):820-835.e10.

How chromosome organization is related to genome function remains poorly understood. Cohesin, loop extrusion, and CCCTC-binding factor (CTCF) have been proposed to create topologically associating domains (TADs) to regulate gene expression. Here, we examine chromosome conformation in embryonic stem cells lacking cohesin and find, as in other cell types, that cohesin is required to create TADs and regulate A/B compartmentalization. However, in the absence of cohesin, we identify a series of long-range chromosomal interactions that persist. These correspond to regions of the genome occupied by the polycomb repressive system and are dependent on PRC1. Importantly, we discover that cohesin counteracts these polycomb-dependent interactions, but not interactions between super-enhancers. This disruptive activity is independent of CTCF and insulation and appears to modulate gene repression by the polycomb system. Therefore, we discover that cohesin disrupts polycomb-dependent chromosome interactions to modulate gene expression in embryonic stem cells.

RevDate: 2020-08-22

Hu G (2020)

Evaluation of 3D Chromatin Interactions Using Hi-C.

Methods in molecular biology (Clifton, N.J.), 2117:65-78.

The invention of Hi-C has greatly facilitated 3D genome research through an unbiased probing of 3D chromatin interactions. It produces enormous amount of sequencing data that capture multiscale chromatin conformation structures. In the last decade, numerous computational methods have been developed to analyze Hi-C data and predict A/B compartments, topologically associating domains (TADs), and significant chromatin contacts. This chapter introduced the iHiC package that provides several utilities to facilitate Hi-C data analysis with public software and demonstrated its application to a Hi-C dataset generated for mouse embryonic stem (ES) cells.

RevDate: 2020-02-10
CmpDate: 2020-02-10

Yang K, Xue Z, X Lv (2020)

Molecular mechanism of the 3D genome structure and function regulation during cell terminal differentiation.

Yi chuan = Hereditas, 42(1):32-44.

The eukaryotic chromatin is folded into highly complex three-dimensional (3D) structures, which plays an important role in the precise regulation of gene expression and normal physiological function. During differentiation and terminal maturation, cells usually undergo dramatic morphology and gene expression changes, accompanied by significant changes in the 3D structure of the genome. In this review, we provide a comprehensive view of the spatial hierarchical organization of the genome, including chromosome territories, A/B compartment, topologically associating domains (TADs) and looping, focusing on recent progresses in the dynamic 3D genomic structural changes and functional regulation during cell differentiation and terminal maturation. In the end, we summarize the unsolved issues as well as prospects of the 3D genome research in cell differentiation and maturation.

RevDate: 2020-04-08
CmpDate: 2020-04-07

Achinger-Kawecka J, Valdes-Mora F, Luu PL, et al (2020)

Epigenetic reprogramming at estrogen-receptor binding sites alters 3D chromatin landscape in endocrine-resistant breast cancer.

Nature communications, 11(1):320.

Endocrine therapy resistance frequently develops in estrogen receptor positive (ER+) breast cancer, but the underlying molecular mechanisms are largely unknown. Here, we show that 3-dimensional (3D) chromatin interactions both within and between topologically associating domains (TADs) frequently change in ER+ endocrine-resistant breast cancer cells and that the differential interactions are enriched for resistance-associated genetic variants at CTCF-bound anchors. Ectopic chromatin interactions are preferentially enriched at active enhancers and promoters and ER binding sites, and are associated with altered expression of ER-regulated genes, consistent with dynamic remodelling of ER pathways accompanying the development of endocrine resistance. We observe that loss of 3D chromatin interactions often occurs coincidently with hypermethylation and loss of ER binding. Alterations in active A and inactive B chromosomal compartments are also associated with decreased ER binding and atypical interactions and gene expression. Together, our results suggest that 3D epigenome remodelling is a key mechanism underlying endocrine resistance in ER+ breast cancer.

RevDate: 2020-02-14
CmpDate: 2020-02-14

Cameron CJ, Dostie J, M Blanchette (2020)

HIFI: estimating DNA-DNA interaction frequency from Hi-C data at restriction-fragment resolution.

Genome biology, 21(1):11.

Hi-C is a popular technique to map three-dimensional chromosome conformation. In principle, Hi-C's resolution is only limited by the size of restriction fragments. However, insufficient sequencing depth forces researchers to artificially reduce the resolution of Hi-C matrices at a loss of biological interpretability. We present the Hi-C Interaction Frequency Inference (HIFI) algorithms that accurately estimate restriction-fragment resolution Hi-C matrices by exploiting dependencies between neighboring fragments. Cross-validation experiments and comparisons to 5C data and known regulatory interactions demonstrate HIFI's superiority to existing approaches. In addition, HIFI's restriction-fragment resolution reveals a new role for active regulatory regions in structuring topologically associating domains.

RevDate: 2020-08-24
CmpDate: 2020-04-08

Beagan JA, JE Phillips-Cremins (2020)

On the existence and functionality of topologically associating domains.

Nature genetics, 52(1):8-16.

Genomes across a wide range of eukaryotic organisms fold into higher-order chromatin domains. Topologically associating domains (TADs) were originally discovered empirically in low-resolution Hi-C heat maps representing ensemble average interaction frequencies from millions of cells. Here, we discuss recent advances in high-resolution Hi-C, single-cell imaging experiments, and functional genetic studies, which provide an increasingly complex view of the genome's hierarchical structure-function relationship. On the basis of these new findings, we update the definitions of distinct classes of chromatin domains according to emerging knowledge of their structural, mechanistic and functional properties.

RevDate: 2020-04-20
CmpDate: 2020-04-20

Khoury A, Achinger-Kawecka J, Bert SA, et al (2020)

Constitutively bound CTCF sites maintain 3D chromatin architecture and long-range epigenetically regulated domains.

Nature communications, 11(1):54.

The architectural protein CTCF is a mediator of chromatin conformation, but how CTCF binding to DNA is orchestrated to maintain long-range gene expression is poorly understood. Here we perform RNAi knockdown to reduce CTCF levels and reveal a shared subset of CTCF-bound sites are robustly resistant to protein depletion. The 'persistent' CTCF sites are enriched at domain boundaries and chromatin loops constitutive to all cell types. CRISPR-Cas9 deletion of 2 persistent CTCF sites at the boundary between a long-range epigenetically active (LREA) and silenced (LRES) region, within the Kallikrein (KLK) locus, results in concordant activation of all 8 KLK genes within the LRES region. CTCF genome-wide depletion results in alteration in Topologically Associating Domain (TAD) structure, including the merging of TADs, whereas TAD boundaries are not altered where persistent sites are maintained. We propose that the subset of essential CTCF sites are involved in cell-type constitutive, higher order chromatin architecture.

RevDate: 2020-02-14
CmpDate: 2020-02-14

Kentepozidou E, Aitken SJ, Feig C, et al (2020)

Clustered CTCF binding is an evolutionary mechanism to maintain topologically associating domains.

Genome biology, 21(1):5.

BACKGROUND: CTCF binding contributes to the establishment of a higher-order genome structure by demarcating the boundaries of large-scale topologically associating domains (TADs). However, despite the importance and conservation of TADs, the role of CTCF binding in their evolution and stability remains elusive.

RESULTS: We carry out an experimental and computational study that exploits the natural genetic variation across five closely related species to assess how CTCF binding patterns stably fixed by evolution in each species contribute to the establishment and evolutionary dynamics of TAD boundaries. We perform CTCF ChIP-seq in multiple mouse species to create genome-wide binding profiles and associate them with TAD boundaries. Our analyses reveal that CTCF binding is maintained at TAD boundaries by a balance of selective constraints and dynamic evolutionary processes. Regardless of their conservation across species, CTCF binding sites at TAD boundaries are subject to stronger sequence and functional constraints compared to other CTCF sites. TAD boundaries frequently harbor dynamically evolving clusters containing both evolutionarily old and young CTCF sites as a result of the repeated acquisition of new species-specific sites close to conserved ones. The overwhelming majority of clustered CTCF sites colocalize with cohesin and are significantly closer to gene transcription start sites than nonclustered CTCF sites, suggesting that CTCF clusters particularly contribute to cohesin stabilization and transcriptional regulation.

CONCLUSIONS: Dynamic conservation of CTCF site clusters is an apparently important feature of CTCF binding evolution that is critical to the functional stability of a higher-order chromatin structure.

RevDate: 2020-09-30

Liu CF, WHW Tang (2019)

Epigenetics in Cardiac Hypertrophy and Heart Failure.

JACC. Basic to translational science, 4(8):976-993.

Heart failure (HF) is a complex syndrome affecting millions of people around the world. Over the past decade, the therapeutic potential of targeting epigenetic regulators in HF has been discussed extensively. Recent advances in next-generation sequencing techniques have contributed substantial progress in our understanding of the role of DNA methylation, post-translational modifications of histones, adenosine triphosphate (ATP)-dependent chromatin conformation and remodeling, and non-coding RNAs in HF pathophysiology. In this review, we summarize epigenomic studies on human and animal models in HF.

RevDate: 2020-08-07
CmpDate: 2020-08-07

Chang LH, Ghosh S, D Noordermeer (2020)

TADs and Their Borders: Free Movement or Building a Wall?.

Journal of molecular biology, 432(3):643-652.

The tridimensional (3D) organization of mammalian genomes combines structures from different length scales. Within this organization, Topologically Associating Domains (TADs) are visible in Hi-C heat maps at the sub-megabase scale. The integrity of TADs is important for correct gene expression, but in a context-dependent and variable manner. The correct structure and function of TADs require the binding of the CTCF protein at both borders, which appears to block an active and dynamic mechanism of "Cohesin-mediated loop extrusion." As a result, mammalian TADs appear as so-called "loop domains" in Hi-C data, which are the focus of this review. Here, we present a reanalysis of TADs from three "golden-standard" mammalian Hi-C data sets. Despite the prominent presence of TADs in Hi-C heat maps from all studies, we find consistently that regions within these domains are only moderately insulated from their surroundings. Moreover, single-cell Hi-C and superresolution microscopy have revealed that the structure of TADs and the position of their borders can vary from cell to cell. The function of TADs as units of gene regulation may thus require additional aspects, potentially incorporating the mechanism of loop extrusion as well. Recent developments in single-cell and multi-contact genomics and superresolution microscopy assays will be instrumental to link TAD formation and structure to their function in transcriptional regulation.

RevDate: 2020-05-11
CmpDate: 2020-05-11

Foissac S, Djebali S, Munyard K, et al (2019)

Multi-species annotation of transcriptome and chromatin structure in domesticated animals.

BMC biology, 17(1):108.

BACKGROUND: Comparative genomics studies are central in identifying the coding and non-coding elements associated with complex traits, and the functional annotation of genomes is a critical step to decipher the genotype-to-phenotype relationships in livestock animals. As part of the Functional Annotation of Animal Genomes (FAANG) action, the FR-AgENCODE project aimed to create reference functional maps of domesticated animals by profiling the landscape of transcription (RNA-seq), chromatin accessibility (ATAC-seq) and conformation (Hi-C) in species representing ruminants (cattle, goat), monogastrics (pig) and birds (chicken), using three target samples related to metabolism (liver) and immunity (CD4+ and CD8+ T cells).

RESULTS: RNA-seq assays considerably extended the available catalog of annotated transcripts and identified differentially expressed genes with unknown function, including new syntenic lncRNAs. ATAC-seq highlighted an enrichment for transcription factor binding sites in differentially accessible regions of the chromatin. Comparative analyses revealed a core set of conserved regulatory regions across species. Topologically associating domains (TADs) and epigenetic A/B compartments annotated from Hi-C data were consistent with RNA-seq and ATAC-seq data. Multi-species comparisons showed that conserved TAD boundaries had stronger insulation properties than species-specific ones and that the genomic distribution of orthologous genes in A/B compartments was significantly conserved across species.

CONCLUSIONS: We report the first multi-species and multi-assay genome annotation results obtained by a FAANG project. Beyond the generation of reference annotations and the confirmation of previous findings on model animals, the integrative analysis of data from multiple assays and species sheds a new light on the multi-scale selective pressure shaping genome organization from birds to mammals. Overall, these results emphasize the value of FAANG for research on domesticated animals and reinforces the importance of future meta-analyses of the reference datasets being generated by this community on different species.

RevDate: 2020-05-11
CmpDate: 2020-05-11

Gan W, Luo J, Li YZ, et al (2019)

A computational method to predict topologically associating domain boundaries combining histone Marks and sequence information.

BMC genomics, 20(Suppl 13):980.

BACKGROUND: The three-dimensional (3D) structure of chromatins plays significant roles during cell differentiation and development. Hi-C and other 3C-based technologies allow us to look deep into the chromatin architectures. Many studies have suggested that topologically associating domains (TAD), as the structure and functional unit, are conserved across different organs. However, our understanding about the underlying mechanism of the TAD boundary formation is still limited.

RESULTS: We developed a computational method, TAD-Lactuca, to infer this structure by taking the contextual information of the epigenetic modification signals and the primary DNA sequence information on the genome. TAD-Lactuca is found stable in the case of multi-resolutions and different datasets. It could achieve high accuracy and even outperforms the state-of-art methods when the sequence patterns were incorporated. Moreover, several transcript factor binding motifs, besides the well-known CCCTC-binding factor (CTCF) motif, were found significantly enriched on the boundaries.

CONCLUSIONS: We provided a low cost, effective method to predict TAD boundaries. Above results suggested the incorporation of sequence features could significantly improve the performance. The sequence motif enrichment analysis indicates several gene regulation motifs around the boundaries, which is consistent with TADs may serve as the functional units of gene regulation and implies the sequence patterns would be important in chromatin folding.

RevDate: 2020-10-07
CmpDate: 2020-10-07

Daban JR (2020)

Supramolecular multilayer organization of chromosomes: possible functional roles of planar chromatin in gene expression and DNA replication and repair.

FEBS letters, 594(3):395-411.

Experimental evidence indicates that the chromatin filament is self-organized into a multilayer planar structure that is densely stacked in metaphase and unstacked in interphase. This chromatin organization is unexpected, but it is shown that diverse supramolecular assemblies, including dinoflagellate chromosomes, are multilayered. The mechanical strength of planar chromatin protects the genome integrity, even when double-strand breaks are produced. Here, it is hypothesized that the chromatin filament in the loops and topologically associating domains is folded within the thin layers of the multilaminar chromosomes. It is also proposed that multilayer chromatin has two states: inactive when layers are stacked and active when layers are unstacked. Importantly, the well-defined topology of planar chromatin may facilitate DNA replication without entanglements and DNA repair by homologous recombination.

RevDate: 2020-08-24
CmpDate: 2020-04-17

Schilit SLP, Menon S, Friedrich C, et al (2020)

SYCP2 Translocation-Mediated Dysregulation and Frameshift Variants Cause Human Male Infertility.

American journal of human genetics, 106(1):41-57.

Unexplained infertility affects 2%-3% of reproductive-aged couples. One approach to identifying genes involved in infertility is to study subjects with this clinical phenotype and a de novo balanced chromosomal aberration (BCA). While BCAs may reduce fertility by production of unbalanced gametes, a chromosomal rearrangement may also disrupt or dysregulate genes important in fertility. One such subject, DGAP230, has severe oligozoospermia and 46,XY,t(20;22)(q13.3;q11.2). We identified exclusive overexpression of SYCP2 from the der(20) allele that is hypothesized to result from enhancer adoption. Modeling the dysregulation in budding yeast resulted in disrupted structural integrity of the synaptonemal complex, a common cause of defective spermatogenesis in mammals. Exome sequencing of infertile males revealed three heterozygous SYCP2 frameshift variants in additional subjects with cryptozoospermia and azoospermia. In sum, this investigation illustrates the power of precision cytogenetics for annotation of the infertile genome, suggests that these mechanisms should be considered as an alternative etiology to that of segregation of unbalanced gametes in infertile men harboring a BCA, and provides evidence of SYCP2-mediated male infertility in humans.

RevDate: 2020-05-11
CmpDate: 2020-05-11

Lesne A, Baudement MO, Rebouissou C, et al (2019)

Exploring Mammalian Genome within Phase-Separated Nuclear Bodies: Experimental Methods and Implications for Gene Expression.

Genes, 10(12):.

The importance of genome organization at the supranucleosomal scale in the control of gene expression is increasingly recognized today. In mammals, Topologically Associating Domains (TADs) and the active/inactive chromosomal compartments are two of the main nuclear structures that contribute to this organization level. However, recent works reviewed here indicate that, at specific loci, chromatin interactions with nuclear bodies could also be crucial to regulate genome functions, in particular transcription. They moreover suggest that these nuclear bodies are membrane-less organelles dynamically self-assembled and disassembled through mechanisms of phase separation. We have recently developed a novel genome-wide experimental method, High-salt Recovered Sequences sequencing (HRS-seq), which allows the identification of chromatin regions associated with large ribonucleoprotein (RNP) complexes and nuclear bodies. We argue that the physical nature of such RNP complexes and nuclear bodies appears to be central in their ability to promote efficient interactions between distant genomic regions. The development of novel experimental approaches, including our HRS-seq method, is opening new avenues to understand how self-assembly of phase-separated nuclear bodies possibly contributes to mammalian genome organization and gene expression.

RevDate: 2020-09-14
CmpDate: 2020-09-14

Chen C, Yu W, Tober J, et al (2019)

Spatial Genome Re-organization between Fetal and Adult Hematopoietic Stem Cells.

Cell reports, 29(12):4200-4211.e7.

Fetal hematopoietic stem cells (HSCs) undergo a developmental switch to become adult HSCs with distinct functional properties. To better understand the molecular mechanisms underlying the developmental switch, we have conducted deep sequencing of the 3D genome, epigenome, and transcriptome of fetal and adult HSCs in mouse. We find that chromosomal compartments and topologically associating domains (TADs) are largely conserved between fetal and adult HSCs. However, there is a global trend of increased compartmentalization and TAD boundary strength in adult HSCs. In contrast, intra-TAD chromatin interactions are much more dynamic and widespread, involving over a thousand gene promoters and distal enhancers. These developmental-stage-specific enhancer-promoter interactions are mediated by different sets of transcription factors, such as TCF3 and MAFB in fetal HSCs, versus NR4A1 and GATA3 in adult HSCs. Loss-of-function studies of TCF3 confirm the role of TCF3 in mediating condition-specific enhancer-promoter interactions and gene regulation in fetal HSCs.

RevDate: 2020-04-24
CmpDate: 2020-04-24

Kempfer R, A Pombo (2020)

Methods for mapping 3D chromosome architecture.

Nature reviews. Genetics, 21(4):207-226.

Determining how chromosomes are positioned and folded within the nucleus is critical to understanding the role of chromatin topology in gene regulation. Several methods are available for studying chromosome architecture, each with different strengths and limitations. Established imaging approaches and proximity ligation-based chromosome conformation capture (3C) techniques (such as DNA-FISH and Hi-C, respectively) have revealed the existence of chromosome territories, functional nuclear landmarks (such as splicing speckles and the nuclear lamina) and topologically associating domains. Improvements to these methods and the recent development of ligation-free approaches, including GAM, SPRITE and ChIA-Drop, are now helping to uncover new aspects of 3D genome topology that confirm the nucleus to be a complex, highly organized organelle.

RevDate: 2020-03-18
CmpDate: 2020-03-18

An L, Yang T, Yang J, et al (2019)

OnTAD: hierarchical domain structure reveals the divergence of activity among TADs and boundaries.

Genome biology, 20(1):282.

The spatial organization of chromatin in the nucleus has been implicated in regulating gene expression. Maps of high-frequency interactions between different segments of chromatin have revealed topologically associating domains (TADs), within which most of the regulatory interactions are thought to occur. TADs are not homogeneous structural units but appear to be organized into a hierarchy. We present OnTAD, an optimized nested TAD caller from Hi-C data, to identify hierarchical TADs. OnTAD reveals new biological insights into the role of different TAD levels, boundary usage in gene regulation, the loop extrusion model, and compartmental domains. OnTAD is available at https://github.com/anlin00007/OnTAD.

RevDate: 2020-03-18
CmpDate: 2020-03-18

Llères D, Moindrot B, Pathak R, et al (2019)

CTCF modulates allele-specific sub-TAD organization and imprinted gene activity at the mouse Dlk1-Dio3 and Igf2-H19 domains.

Genome biology, 20(1):272.

BACKGROUND: Genomic imprinting is essential for mammalian development and provides a unique paradigm to explore intra-cellular differences in chromatin configuration. So far, the detailed allele-specific chromatin organization of imprinted gene domains has mostly been lacking. Here, we explored the chromatin structure of the two conserved imprinted domains controlled by paternal DNA methylation imprints-the Igf2-H19 and Dlk1-Dio3 domains-and assessed the involvement of the insulator protein CTCF in mouse cells.

RESULTS: Both imprinted domains are located within overarching topologically associating domains (TADs) that are similar on both parental chromosomes. At each domain, a single differentially methylated region is bound by CTCF on the maternal chromosome only, in addition to multiple instances of bi-allelic CTCF binding. Combinations of allelic 4C-seq and DNA-FISH revealed that bi-allelic CTCF binding alone, on the paternal chromosome, correlates with a first level of sub-TAD structure. On the maternal chromosome, additional CTCF binding at the differentially methylated region adds a further layer of sub-TAD organization, which essentially hijacks the existing paternal-specific sub-TAD organization. Perturbation of maternal-specific CTCF binding site at the Dlk1-Dio3 locus, using genome editing, results in perturbed sub-TAD organization and bi-allelic Dlk1 activation during differentiation.

CONCLUSIONS: Maternal allele-specific CTCF binding at the imprinted Igf2-H19 and the Dlk1-Dio3 domains adds an additional layer of sub-TAD organization, on top of an existing three-dimensional configuration and prior to imprinted activation of protein-coding genes. We speculate that this allele-specific sub-TAD organization provides an instructive or permissive context for imprinted gene activation during development.

RevDate: 2020-03-19

Barajas-Mora EM, AJ Feeney (2020)

Enhancers as regulators of antigen receptor loci three-dimensional chromatin structure.

Transcription, 11(1):37-51.

Enhancers are defined as regulatory elements that control transcription in a cell-type and developmental stage-specific manner. They achieve this by physically interacting with their cognate gene promoters. Significantly, these interactions can occur through long genomic distances since enhancers may not be near their cognate promoters. The optimal coordination of enhancer-regulated transcription is essential for the function and identity of the cell. Although great efforts to fully understand the principles of this type of regulation are ongoing, other potential functions of the long-range chromatin interactions (LRCIs) involving enhancers are largely unexplored. We recently uncovered a new role for enhancer elements in determining the three-dimensional (3D) structure of the immunoglobulin kappa (Igκ) light chain receptor locus suggesting a structural function for these DNA elements. This enhancer-mediated locus configuration shapes the resulting Igκ repertoire. We also propose a role for enhancers as critical components of sub-topologically associating domain (subTAD) formation and nuclear spatial localization.

RevDate: 2020-09-03

van Schoonhoven A, Huylebroeck D, Hendriks RW, et al (2020)

3D genome organization during lymphocyte development and activation.

Briefings in functional genomics, 19(2):71-82.

Chromosomes have a complex three-dimensional (3D) architecture comprising A/B compartments, topologically associating domains and promoter-enhancer interactions. At all these levels, the 3D genome has functional consequences for gene transcription and therefore for cellular identity. The development and activation of lymphocytes involves strict control of gene expression by transcription factors (TFs) operating in a three-dimensionally organized chromatin landscape. As lymphocytes are indispensable for tissue homeostasis and pathogen defense, and aberrant lymphocyte activity is involved in a wide range of human morbidities, acquiring an in-depth understanding of the molecular mechanisms that control lymphocyte identity is highly relevant. Here we review current knowledge of the interplay between 3D genome organization and transcriptional control during B and T lymphocyte development and antigen-dependent activation, placing special emphasis on the role of TFs.

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RJR Experience and Expertise

Researcher

Robbins holds BS, MS, and PhD degrees in the life sciences. He served as a tenured faculty member in the Zoology and Biological Science departments at Michigan State University. He is currently exploring the intersection between genomics, microbial ecology, and biodiversity — an area that promises to transform our understanding of the biosphere.

Educator

Robbins has extensive experience in college-level education: At MSU he taught introductory biology, genetics, and population genetics. At JHU, he was an instructor for a special course on biological database design. At FHCRC, he team-taught a graduate-level course on the history of genetics. At Bellevue College he taught medical informatics.

Administrator

Robbins has been involved in science administration at both the federal and the institutional levels. At NSF he was a program officer for database activities in the life sciences, at DOE he was a program officer for information infrastructure in the human genome project. At the Fred Hutchinson Cancer Research Center, he served as a vice president for fifteen years.

Technologist

Robbins has been involved with information technology since writing his first Fortran program as a college student. At NSF he was the first program officer for database activities in the life sciences. At JHU he held an appointment in the CS department and served as director of the informatics core for the Genome Data Base. At the FHCRC he was VP for Information Technology.

Publisher

While still at Michigan State, Robbins started his first publishing venture, founding a small company that addressed the short-run publishing needs of instructors in very large undergraduate classes. For more than 20 years, Robbins has been operating The Electronic Scholarly Publishing Project, a web site dedicated to the digital publishing of critical works in science, especially classical genetics.

Speaker

Robbins is well-known for his speaking abilities and is often called upon to provide keynote or plenary addresses at international meetings. For example, in July, 2012, he gave a well-received keynote address at the Global Biodiversity Informatics Congress, sponsored by GBIF and held in Copenhagen. The slides from that talk can be seen HERE.

Facilitator

Robbins is a skilled meeting facilitator. He prefers a participatory approach, with part of the meeting involving dynamic breakout groups, created by the participants in real time: (1) individuals propose breakout groups; (2) everyone signs up for one (or more) groups; (3) the groups with the most interested parties then meet, with reports from each group presented and discussed in a subsequent plenary session.

Designer

Robbins has been engaged with photography and design since the 1960s, when he worked for a professional photography laboratory. He now prefers digital photography and tools for their precision and reproducibility. He designed his first web site more than 20 years ago and he personally designed and implemented this web site. He engages in graphic design as a hobby.

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E-mail: RJR8222@gmail.com

Collection of publications by R J Robbins

Reprints and preprints of publications, slide presentations, instructional materials, and data compilations written or prepared by Robert Robbins. Most papers deal with computational biology, genome informatics, using information technology to support biomedical research, and related matters.

Research Gate page for R J Robbins

ResearchGate is a social networking site for scientists and researchers to share papers, ask and answer questions, and find collaborators. According to a study by Nature and an article in Times Higher Education , it is the largest academic social network in terms of active users.

Curriculum Vitae for R J Robbins

short personal version

Curriculum Vitae for R J Robbins

long standard version

RJR Picks from Around the Web (updated 11 MAY 2018 )