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CTCF and cohesin regulate chromatin loop stability with distinct dynamics.

ABSTRACT: Folding of mammalian genomes into spatial domains is critical for gene regulation. The insulator protein CTCF and cohesin control domain location by folding domains into loop structures, which are widely thought to be stable. Combining genomic and biochemical approaches we show that CTCF and cohesin co-occupy the same sites and physically interact as a biochemically stable complex. However, using single-molecule imaging we find that CTCF binds chromatin much more dynamically than cohesin (~1-2 min vs. ~22 min residence time). Moreover, after unbinding, CTCF quickly rebinds another cognate site unlike cohesin for which the search process is long (~1 min vs. ~33 min). Thus, CTCF and cohesin form a rapidly exchanging 'dynamic complex' rather than a typical stable complex. Since CTCF and cohesin are required for loop domain formation, our results suggest that chromatin loops are dynamic and frequently break and reform throughout the cell cycle.

SUBMITTER: Hansen AS

PROVIDER: S-EPMC5446243 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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CTCF and cohesin regulate chromatin loop stability with distinct dynamics.

Hansen Anders S AS Pustova Iryna I Cattoglio Claudia C Tjian Robert R Darzacq Xavier X

eLife 20170503

Folding of mammalian genomes into spatial domains is critical for gene regulation. The insulator protein CTCF and cohesin control domain location by folding domains into loop structures, which are widely thought to be stable. Combining genomic and biochemical approaches we show that CTCF and cohesin co-occupy the same sites and physically interact as a biochemically stable complex. However, using single-molecule imaging we find that CTCF binds chromatin much more dynamically than cohesin (~1-2 m ...[more]

PMID: 28467304

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CTCF and cohesin regulate chromatin loop stability with distinct dynamics

Project description:The study investigates the nuclear organization and the binding dynamics of CTCF and cohesin by super-resolution microscopy and ChIP-seq. We determined the genome-wide binding profile of CTCF and Rad21 cohesin subunit in wild type mouse ES cells and compared them to a double FLAG-Halo-mCTCF/mRad21-SNAPf-V5 knock-in mES line, generated by CRISPR/Cas9-mediated genome editing to perform imaging experiments.

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Project description:The DNA-binding protein CCCTC-binding factor (CTCF) and the cohesin complex function together to shape chromatin architecture in mammalian cells, but the molecular details of this process remain unclear. Here, we demonstrate that a 79-aa region within the CTCF N terminus is essential for cohesin positioning at CTCF binding sites and chromatin loop formation. However, the N terminus of CTCF fused to artificial zinc fingers was not sufficient to redirect cohesin to non-CTCF binding sites, indicating a lack of an autonomously functioning domain in CTCF responsible for cohesin positioning. BORIS (CTCFL), a germline-specific paralog of CTCF, was unable to anchor cohesin to CTCF DNA binding sites. Furthermore, CTCF-BORIS chimeric constructs provided evidence that, besides the N terminus of CTCF, the first two CTCF zinc fingers, and likely the 3D geometry of CTCF-DNA complexes, are also involved in cohesin retention. Based on this knowledge, we were able to convert BORIS into CTCF with respect to cohesin positioning, thus providing additional molecular details of the ability of CTCF to retain cohesin. Taken together, our data provide insight into the process by which DNA-bound CTCF constrains cohesin movement to shape spatiotemporal genome organization.

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