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Cohesin-based chromatin interactions enable regulated gene expression within pre-existing architectural compartments.

ABSTRACT: Chromosome conformation capture approaches have shown that interphase chromatin is organized into an architectural framework of Mb-sized compartments and sub-Mb-sized topological domains. Cohesin controls chromosome topology to facilitate DNA repair and chromosome segregation in cycling cells, and also associates with active enhancers and promoters and with CTCF to form long-range interactions important for gene regulation. We find that architectural compartments - a major feature of interphase chromatin organization – are maintained in non-cycling mouse thymocytes after genetic depletion of cohesin in vivo. Cohesin was however required for specific long-range interactions within permissive (A-type) compartments, where cohesin-regulated genes reside. Cohesin depletion diminished interactions between cohesin-bound sites, while alternative interactions between chromatin features associated with transcriptional activation and repression became more prominent, with corresponding changes in gene expression. Our findings indicate that cohesin-mediated long-range interactions facilitate discrete gene expression states within pre-existing chromosomal compartments.

ORGANISM(S): Mus musculus

PROVIDER: GSE48763 | GEO | 2013/08/13

SECONDARY ACCESSION(S): PRJNA211477

REPOSITORIES: GEO

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Project description:Eukaryotic genomes are folded into a hierarchy of three-dimensional structures that impact nuclear functions, including transcription, replication, and repair1-3. Studies in Drosophila and mammals have revealed megabase-sized topologically associated domains (TADs) within chromosomes, which in turn are spatially restricted within the nucleus4-8. However, little is known about local physical constraints that drive higher-order folding of chromosomes. Here we performed Hi-C analysis of the fission yeast Schizosaccharomyces pombe to explore genome organization at high resolution. S. pombe comprises a small genome ideal for examining structural features of chromatin folding, and contains fundamental components present in higher eukaryotes. Large domains of heterochromatin coat centromeres and telomeres and recruit cohesin, a ring-like protein complex that binds sister chromatids and mediates long range looping of interphase chromosomes. Our analyses reveal a highly ordered chromosome organization, consistent with a Rabl configuration, which is dependent on constraints imposed at centromeres and telomeres. We find that local chromatin compaction and cohesin recruitment to centromeres mediated by heterochromatin is required for maintaining global genome territorial restraint. In addition to larger complex domains, we also observed locally interacting regions of chromatin ~50 kilobases long, which organize chromosome arms into structures referred to as “globules”. Globule boundaries are enriched in cohesin and convergent gene orientation. The role of cohesin in maintaining globule domains is independent of its role in sister chromatid cohesion, as globule domains are also a feature of G1 chromosome architecture. Defect in cohesin disrupts globule domains and results in an altered chromosome organization at larger scales, including the loss of chromosome territories. Disruption of globules also affects functional annotation of the genome, leading to impairment of borders between neighboring transcriptional units. Our analyses reveal key features of chromatin organization and folding and show that distinct mechanisms uniquely impact the hierarchy of genome organization to protect genome integrity and to coordinate nuclear functions. Comparison of HiC contact maps under various conditions reveal fundamental principles of genome organization

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Cohesin-based chromatin interactions enable regulated gene expression within pre-existing architectural compartments.

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