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The structural basis for cohesin/CTCF anchored loops [ChIP-seq]

ABSTRACT: 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.

ORGANISM(S): Homo sapiens

PROVIDER: GSE126634 | GEO | 2020/01/07

REPOSITORIES: GEO

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The structural basis for cohesin/CTCF anchored loops [Hi-C]

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.

2020-01-07 | GSE126636 | GEO

The structural basis for cohesin/CTCF anchored loops [RNA-seq]

2020-01-07 | GSE126635 | GEO

Sensitivity of cohesin-chromatin association to high salt treatment corroborates non-topological mode of loop extrusion

Project description:Cohesin is a key organizer of chromatin folding in eukaryotic cells. Two basic activities of this ring-shaped protein complex are maintenance of sister chromatid cohesion and establishment of long-range DNA-DNA interactions through the process of loop extrusion. Though basic principles of both cohesion and loop extrusion have been described we still do not understand several crucial mechanistic details. One of such unresolved issues is the question of whether a cohesin ring topologically embraces DNA string(s) during loop extrusion. Here we show that cohesin complexes residing on CTCF-occupied genomic sites in mammalian cells do not interact with DNA topologically. We assessed stability of cohesin-dependent loops and cohesin association with chromatin in high ionic strength conditions in G1-synchronised HeLa cells. We found that increased salt concentration completely displaces cohesin from those genomic regions which correspond to CTCF-defined loop anchors. Unsurprisingly, CTCF-anchored cohesin loops also dissipate in these conditions. As topologically-engaged cohesin is considered to be salt-resistant, our data corroborate a non-topological model of loop extrusion.

2021-07-20 | GSE166387 | GEO

The cohesin acetylation cycle controls chromatin loop length through a PDS5A brake mechanism

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.

2022-03-14 | PXD032185 | Pride

Wapl-mediated release of Scc1-cohesin regulates chromosome structure and segregation in mouse oocytes

Project description:Cohesin is essential for genome folding and chromosome inheritance through cell divisions. In somatic cells, both of these functions are mediated by Scc1-cohesin, which in mitosis is released from chromosomes by Wapl and separase. In mammalian oocytes, cohesion is mediated by Rec8-cohesin. Scc1 is also expressed but neither required nor sufficient for cohesion, and its function in oocytes is unknown. Likewise, it is unknown whether Wapl regulates one or both cohesin complexes and chromosome segregation in mature oocytes. Using conditional mouse mutagenesis, we show that in meiosis I Wapl is required for proper chromosome segregation, predominantly releases Scc1-cohesin from chromosomes and promotes production of euploid eggs. Using single-nucleus Hi-C, we found that Scc1 is essential for chromatin loops and topologically associating domains (TADs) in oocytes. Increasing Scc1 residence time on chromosomes by Wapl depletion leads to vermicelli formation and intra-loop structures but, unlike in mitotic cells, does not increase loop size. This implies that loop size has reached a maximum in oocytes, possibly because it is limited by barriers such as cohesive cohesin. We conclude that distinct cohesin complexes generate loops and cohesion in mammalian oocytes and propose that the same principle applies to all cell types and species.

2020-03-04 | GSE132264 | GEO

MCM complexes are barriers that restrict cohesin-mediated loop extrusion [RNA-Seq]

Project description:Eukaryotic genomes are compacted into loops and topologically associating domains (TADs), which contribute to transcription, recombination and genomic stability. Cohesin extrudes DNA into loops that are thought to lengthen until CTCF boundaries are encountered. Little is known about whether loop extrusion is impeded by DNA-bound machines. Here we show that the minichromosome maintenance (MCM) complex is a barrier that restricts loop extrusion in G1 phase. Single-nucleus Hi-C of mouse zygotes revealed that MCM loading reduces CTCF-anchored loops and decreases TAD boundary insulation, suggesting loop extrusion is impeded before reaching CTCF. This effect extends to HCT116 cells, where MCMs affect the number of CTCF-anchored loops and gene expression. Simulations suggest that MCMs are abundant, randomly positioned, partially permeable barriers. Single-molecule imaging shows that MCMs are physical barriers that frequently constrain cohesin translocation in vitro. Remarkably, chimaeric yeast MCMs harbouring a cohesin-interaction motif from human MCM3 induce cohesin pausing, suggesting that MCMs are “active” barriers with binding sites. These findings raise the possibility that cohesin can arrive by loop extrusion at MCMs, which determine the genomic sites at which sister chromatid cohesion is established. Based on in vivo, in silico and in vitro data, we conclude that distinct loop extrusion barriers shape the 3D genome.

2022-03-08 | GSE196496 | GEO

ESCO1 and CTCF enable formation of long chromatin loops by protecting cohesin-STAG1 from WAPL

Project description:The human genome folds to create thousands of loops connecting sites that are bound by the insulator protein CTCF and the ring-shaped cohesin complex. It is thought that most of these loops emerge through a process whereby cohesin extrudes chromatin, forming an initially small loop that grows larger and larger until the loop’s expansion is arrested by CTCF. Cohesin rings comprise four proteins: SMC1, SMC3, SCC1, and, in higher eukaryotes, either STAG1 or STAG2. We explore differential roles of especially STAG1, STAG2 and ESCO1 proteins in chromatin organization.

2020-02-27 | GSE138405 | GEO

The cohesin release factor WAPL restricts chromatin loop extension. [HiC-Seq]

Project description:The spatial organization of chromosomes influences many nuclear processes including gene expression. The cohesin complex shapes the 3D genome by looping together CTCF sites along chromosomes. We show here that chromatin loop size can be increased, and that the duration with which cohesin embraces DNA determines the degree to which loops are enlarged. Cohesin’s DNA release factor WAPL restricts the degree of this loop extension and also prevents looping between incorrectly oriented CTCF sites. We reveal that the SCC2/SCC4 complex promotes the extension of chromatin loops and the formation of topologically associated domains (TADs). Our data support the model that cohesin structures chromosomes through the processive enlargement of loops and that TADs reflect polyclonal collections of loops in the making. Finally, we find that whereas cohesin promotes chromosomal looping, it rather limits nuclear compartmentalization. We conclude that the balanced activity of SCC2/SCC4 and WAPL enables cohesin to correctly structure chromosomes.

2017-05-03 | GSE95014 | GEO

The cohesin release factor WAPL restricts chromatin loop extension. [RNA-Seq]

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The cohesin release factor WAPL restricts chromatin loop extension. [ChIP-Seq]

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