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Cohesin chromatin loop formation by an extrinsic motor (ChIP-Seq)

ABSTRACT: The ring-shaped cohesin complex topologically entraps two DNAs to establish sister chromatid cohesion. Cohesin also shapes the interphase chromatin landscape, with wide-ranging implications for gene regulation, which cohesin is thought to achieve by actively extruding DNA loops without topologically entrapping DNA. The ‘loop extrusion’ model find motivation from in vitro observations - whether this process indeed underlies chromatin loop formation in vivo remains untested. Here, using the budding yeast S. cerevisiae, we generate cohesin variants that have lost their ability to extrude DNA loops but retain their ability to topologically entrap DNA. Analysis of these variants suggests that in vivo chromatin loops form independently of loop extrusion. Instead, we find that transcription promotes loop formation, likely by generating DNA substrates for topological loop capture. Transcription furthermore acts as an extrinsic motor that, by pushing cohesin along transcription units, extends chromatin loops and defines their ultimate positions. Our results necessitate a re-evaluation of the loop extrusion hypothesis and point to an alternative mechanism for cohesin-dependent chromatin organisation. Loop formation by DNA-DNA capture, akin to sister chromatid cohesion establishment at replication forks, unifies cohesin’s two roles in chromosome segregation and interphase genome organisation.

ORGANISM(S): Saccharomyces cerevisiae Nakaseomyces glabratus

PROVIDER: GSE248280 | GEO | 2024/08/04

REPOSITORIES: GEO

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Cohesin chromatin loop formation by an extrinsic motor (Micro-C)

Project description:The ring-shaped cohesin complex topologically entraps two DNAs to establish sister chromatid cohesion. Cohesin also shapes the interphase chromatin landscape, with wide-ranging implications for gene regulation, which cohesin is thought to achieve by actively extruding DNA loops without topologically entrapping DNA. The ‘loop extrusion’ model find motivation from in vitro observations - whether this process indeed underlies chromatin loop formation in vivo remains untested. Here, using the budding yeast S. cerevisiae, we generate cohesin variants that have lost their ability to extrude DNA loops but retain their ability to topologically entrap DNA. Analysis of these variants suggests that in vivo chromatin loops form independently of loop extrusion. Instead, we find that transcription promotes loop formation, likely by generating DNA substrates for topological loop capture. Transcription furthermore acts as an extrinsic motor that, by pushing cohesin along transcription units, extends chromatin loops and defines their ultimate positions. Our results necessitate a re-evaluation of the loop extrusion hypothesis and point to an alternative mechanism for cohesin-dependent chromatin organisation. Loop formation by DNA-DNA capture, akin to sister chromatid cohesion establishment at replication forks, unifies cohesin’s two roles in chromosome segregation and interphase genome organisation.

2024-08-04 | GSE248281 | 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

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

SCC1 interaction proteomics in Saccharomyces cerevisiae

Project description:FACT mediates cohesin function on chromatin Cohesin is a key regulator of genome architecture with roles in sister chromatid cohesion and the organisation of higher-order structures during interphase and mitosis. The recruitment and mobility of cohesin complexes on DNA are restricted by nucleosomes. Here we show that cohesin role in chromosome organization requires the histone chaperone FACT. Depletion of FACT in metaphase cells affects cohesin stability on chromatin reducing its accumulation at pericentric regions and binding on chromosome arms. Using Hi-C, we show that cohesin-dependent TAD (Topological Associated Domains)-like structures in G1 and metaphase chromosomes are disrupted in the absence of FACT. Surprisingly, sister chromatid cohesion is intact in FACT-depleted cells, although chromosome segregation failure is observed. Our results uncover a role for FACT in genome organisation by facilitating cohesin dependent compartmentalization of chromosomes into loop domains.

2019-10-03 | PXD014896 | Pride

Absolute quantification of cohesin and its regulators in human cells

Project description:The organisation of mammalian genomes into loops and topologically associated domains (TADs) regulates gene expression. The formation and maintenance of loops and TADs depends on the protein complex cohesin, which also holds replicated sister chromatids together from S phase until mitosis. To understand how cohesin functions, it is essential to know how many cohesin complexes and regulators exist in a typical cell and how they are distributed genome-wide. Here, we have used quantitative mass spectrometry, fluorescence-correlation spectroscopy and fluorescence recovery after photobleaching to measure the absolute number and dynamics of core subunits and regulators of the cohesin complex in human cells. We find that 60000 – 134000 cohesin complexes are bound to chromatin per G1 HeLa cell, suggesting that cohesin most likely does not occupy all its binding sites concurrently. We incorporate our data into mathematical models and discuss implications for how cohesin might contribute to genome organisation and sister chromatid cohesion.

2019-11-13 | PXD012712 | Pride

Cohesin mediates DNA loop extrusion and sister chromatid cohesion by distinct mechanisms [Hi-C]

Project description:Cohesin connects CTCF binding sites and other genomic loci in cis to form chromatin loops, and replicated DNA molecules in trans to mediate sister chromatid cohesion. Whether cohesin uses distinct or related mechanisms to perform these functions is unknown. Here we describe a cohesin hinge mutant, which can extrude DNA into loops but is unable to mediate cohesion. Our results suggest that the latter defect arises during cohesion establishment. The observation that cohesin’s cohesion and loop extrusion activities can be separated indicates that cohesin uses distinct mechanisms to perform these two functions. Unexpectedly, the same hinge mutant can also not be stopped by CTCF boundaries as well as wildtype cohesin. This suggests that cohesion establishment and cohesin’s interaction with CTCF boundaries depend on related mechanisms and raises the possibility that both require transient hinge opening to entrap DNA inside the cohesin ring.

2023-10-25 | GSE235771 | GEO

Cohesin mediates DNA loop extrusion and sister chromatid cohesion by distinct mechanisms [ChIP-seq]

2023-10-25 | GSE235770 | GEO

FACT mediates cohesin function on chromatin

Project description:Cohesin is a key regulator of genome architecture with roles in sister chromatid cohesion and the organisation of higher-order structures during interphase and mitosis. The recruitment and mobility of cohesin complexes on DNA are restricted by nucleosomes. Here we show that cohesin role in chromosome organization requires the histone chaperone FACT. Depletion of FACT in metaphase cells affects cohesin stability on chromatin reducing its accumulation at pericentric regions and binding on chromosome arms. Using Hi-C, we show that cohesin-dependent TAD (Topological Associated Domains)-like structures in G1 and metaphase chromosomes are disrupted in the absence of FACT. Surprisingly, sister chromatid cohesion is intact in FACT-depleted cells, although chromosome segregation failure is observed. Our results uncover a role for FACT in genome organisation by facilitating cohesin dependent compartmentalization of chromosomes into loop domains.

2019-10-11 | GSE118534 | GEO

Response of cohesin STAG1 and STAG2 to reduction of NIPBL levels [Hi-C]

Project description:Cohesin mediates sister chromatid cohesion and organizes the genome through the formation of chromatin loops. Two versions of the complex carrying either STAG1 or STAG2 show overlapping and specific functions and both are required to fulfill embryonic development. Cohesin-STAG1 displays longer residence time on chromatin that depends on CTCF and ESCO1 and establishes longer, long-lived chromatin loops together with CTCF. Cohesin-STAG2 shows a preferential interaction with WAPL and mediates shorter loops involved in tissue-specific transcription independently of CTCF. Here we show that the two variants respond in opposite ways to knock down of NIPBL, the putative cohesin loader that is also essential for loop extrusion. Cohesin-STAG1 levels increase on chromatin under this condition and the complex accumulates further at CTCF positions while cohesin-STAG2 is diminished genome-wide. Our data support a model in which NIPBL is not required for association of cohesin with chromatin but it is for loop extrusion, which in turn facilitates stabilization of cohesin-STAG2 at CTCF positions after being loaded elsewhere. In contrast, cohesin-STAG1 is preferentially loaded at CTCF sites independently of NIPBL. Nevertheless, loop formation by these chromatin-bound complexes is impaired and gene expression is severely affected, resembling alterations in Cornelia de Lange patients

2023-01-30 | GSE207115 | GEO

Response of cohesin STAG1 and STAG2 to reduction of NIPBL levels [ChIP-Seq]

2023-01-30 | GSE207113 | GEO

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