Project description:Physical interactions between distal regulatory elements in the genome play a key role in regulating gene expression, yet the extent to which these interactions vary between cell types and contribute to cell type-specific gene expression patterns remains unclear. To address this question we have mapped cohesin-bound chromatin loops in 24 diverse human cell types at high resolution using the chromatin interaction analysis by paired-end tag (ChIA-PET) sequencing approach. We combined a total of ~9.6 billion reads across all samples to generate a compendium of 124,830 loops, the most extensive resource currently available. We find that 39% of all chromatin loops vary across cell types, and such changes are effective at grouping cell types based on their tissue of origin, indicating commonalities in three-dimensional (3D) genome architecture amongst related cell types. In contrast, different cell types derived from the same individual show markedly different patterns of interactions indicating that the observed differences are mainly caused by epigenetic changes. Variation in chromatin loops correlates with changes in gene expression, especially for long-range contacts linking cell type-specific enhancers to promoters; moreover, genes contained within the same loop show coordinated co-expression changes in expression across cell types. We further find that loops specific to either blood or embryonic cell lines harbor distinct sets of genes relevant to cell type-specific function, and are enriched for lineage determining transcription factors, indicating a possible mechanism for the assembly of variable loops. Finally, we demonstrate that genetic variants identified in GWAS are enriched in variable loops in disease relevant cell types. Our results provide important insights in how changes in 3D chromatin organization potentially regulate cell type-specific functions.
Project description:Physical interactions between distal regulatory elements in the genome play a key role in regulating gene expression, yet the extent to which these interactions vary between cell types and contribute to cell type-specific gene expression patterns remains unclear. To address this question we have mapped cohesin-bound chromatin loops in 24 diverse human cell types at high resolution using the chromatin interaction analysis by paired-end tag (ChIA-PET) sequencing approach. We combined a total of ~9.6 billion reads across all samples to generate a compendium of 124,830 loops, the most extensive resource currently available. We find that 39% of all chromatin loops vary across cell types, and such changes are effective at grouping cell types based on their tissue of origin, indicating commonalities in three-dimensional (3D) genome architecture amongst related cell types. In contrast, different cell types derived from the same individual show markedly different patterns of interactions indicating that the observed differences are mainly caused by epigenetic changes. Variation in chromatin loops correlates with changes in gene expression, especially for long-range contacts linking cell type-specific enhancers to promoters; moreover, genes contained within the same loop show coordinated co-expression changes in expression across cell types. We further find that loops specific to either blood or embryonic cell lines harbor distinct sets of genes relevant to cell type-specific function, and are enriched for lineage determining transcription factors, indicating a possible mechanism for the assembly of variable loops. Finally, we demonstrate that genetic variants identified in GWAS are enriched in variable loops in disease relevant cell types. Our results provide important insights in how changes in 3D chromatin organization potentially regulate cell type-specific functions.
Project description:Physical interactions between distal regulatory elements in the genome play a key role in regulating gene expression, yet the extent to which these interactions vary between cell types and contribute to cell type-specific gene expression patterns remains unclear. To address this question we have mapped cohesin-bound chromatin loops in 24 diverse human cell types at high resolution using the chromatin interaction analysis by paired-end tag (ChIA-PET) sequencing approach. We combined a total of ~9.6 billion reads across all samples to generate a compendium of 124,830 loops, the most extensive resource currently available. We find that 39% of all chromatin loops vary across cell types, and such changes are effective at grouping cell types based on their tissue of origin, indicating commonalities in three-dimensional (3D) genome architecture amongst related cell types. In contrast, different cell types derived from the same individual show markedly different patterns of interactions indicating that the observed differences are mainly caused by epigenetic changes. Variation in chromatin loops correlates with changes in gene expression, especially for long-range contacts linking cell type-specific enhancers to promoters; moreover, genes contained within the same loop show coordinated co-expression changes in expression across cell types. We further find that loops specific to either blood or embryonic cell lines harbor distinct sets of genes relevant to cell type-specific function, and are enriched for lineage determining transcription factors, indicating a possible mechanism for the assembly of variable loops. Finally, we demonstrate that genetic variants identified in GWAS are enriched in variable loops in disease relevant cell types. Our results provide important insights in how changes in 3D chromatin organization potentially regulate cell type-specific functions.
Project description:Physical interactions between distal regulatory elements have a key role in regulating gene expression, but the extent to which these interactions vary between cell types and contribute to cell-type-specific gene expression remains unclear. Here, to address these questions as part of phase III of the Encyclopedia of DNA Elements (ENCODE), we mapped cohesin-mediated chromatin loops, using chromatin interaction analysis by paired-end tag sequencing (ChIA-PET), and analysed gene expression in 24 diverse human cell types, including core ENCODE cell lines. Twenty-eight per cent of all chromatin loops vary across cell types; these variations modestly correlate with changes in gene expression and are effective at grouping cell types according to their tissue of origin. The connectivity of genes corresponds to different functional classes, with housekeeping genes having few contacts, and dosage-sensitive genes being more connected to enhancer elements. This atlas of chromatin loops complements the diverse maps of regulatory architecture that comprise the ENCODE Encyclopedia, and will help to support emerging analyses of genome structure and function.
Project description:Cohesin is implicated in establishing tissue-specific DNA loops that target enhancers to promoters, and also localizes to sites bound by the insulator protein CTCF, which blocks enhancer-promoter communication. However, cohesin-associated interactions have not been characterized on a genome-wide scale. Here we performed chromatin interaction analysis with paired-end tag sequencing (ChIA-PET) of the cohesin subunit SMC1A in developing mouse limb. We identified 2,264 SMC1A interactions, of which 1,491 (65%) involved sites co-occupied by CTCF. SMC1A participates in tissue- specific enhancer-promoter interactions and interactions that demarcate regions of correlated regulatory output. In contrast to previous studies, we also identified interactions between promoters and distal sites that are maintained in multiple tissues, but are poised in embryonic stem cells and resolve to tissue-specific activated or repressed chromatin states in the mouse embryo. Our results reveal the diversity of cohesin- associated interactions in the genome and highlight their role in establishing the regulatory architecture of development. Smc1a ChIA-PET, RNA-seq, chromatin state maps (H3K27ac, H3K27me3, H3K4m2), and CTCF and Smc1a binding in mouse embryonic limb bud (E11.5)
Project description:Cohesin structures the genome through the formation of chromatin loops and by holding together the sister chromatids. The acetylation of cohesin’s SMC3 subunit is a dynamic process that involves the acetyltransferase ESCO1 and deacetylase HDAC8. Here we show that this cohesin acetylation cycle controls the 3D genome. ESCO1 restricts the length of chromatin loops and architectural stripes, while HDAC8 promotes the extension of such loops and stripes. This role in controlling loop length turns out to be distinct from the canonical role of cohesin acetylation that protects against WAPL-mediated DNA release. We reveal that acetylation rather controls cohesin’s interaction with PDS5A to restrict chromatin loop length. Our data supports a model in which this PDS5A-bound state acts as a brake that enables the pausing and restart of loop enlargement. The cohesin acetylation cycle hereby provides punctuation in the process of genome folding.
Project description:Cohesin catalyses the folding of the genome into loops that are anchored by CTCF. The molecular mechanism of how cohesin and CTCF structure the 3D genome has remained unclear. Here we show that a segment within the CTCF N terminus interacts with the SA2-SCC1 subunits of cohesin. A 2.6 Å crystal structure of SA2-SCC1 in complex with CTCF reveals the molecular basis of the interaction. We demonstrate that this interaction is specifically required for CTCF-anchored loops and contributes to the positioning of cohesin at CTCF-binding sites. A similar motif is present in a number of established and novel cohesin ligands, including the cohesin release factor WAPL. Our data suggest that CTCF enables chromatin loop formation by protecting cohesin against loop release. These results provide fundamental insights into the molecular mechanism that enables dynamic regulation of chromatin folding by cohesin and CTCF.