Biology subjects

Stocsits, R.

Publications and source records attributed to Stocsits, R..

2 recordsLinked to original sources

bioRxiv2018

Dynamics of sister chromatid resolution during cell cycle progression

Faithful genome transmission in dividing cells requires that the two copies of each chromosomes DNA package into separate, but physically linked, sister chromatids. The linkage between sister chromatids is mediated by cohesin, yet where sister chromatids are linked and how they resolve during cell cycle progression has remained unclear. Here, we investigated sister chromatid organization in live human cells using dCas9-mEGFP labelling of endogenous genomic loci. We detected substantial sister locus separation during G2 phase, irrespective of the proximity to cohesin enrichment sites. Almost all sister loci separated within a few hours after their respective replication, and then rapidly equilibrated their average distances within dynamic chromatin polymers. Our findings explain why the topology of sister chromatid resolution in G2 largely reflects the DNA replication program. Further, these data suggest that cohesin enrichment sites are not persistent cohesive sites in human cells. Rather, cohesion might occur at variable genomic positions within the cell population.

cell biology↗

bioRxiv2017

CTCF, WAPL and PDS5 proteins control the formation of TADs and loops by cohesin

Mammalian genomes are organized into compartments, topologically-associating domains (TADs) and loops to facilitate gene regulation and other chromosomal functions. Compartments are formed by nucleosomal interactions, but how TADs and loops are generated is unknown. It has been proposed that cohesin forms these structures by extruding loops until it encounters CTCF, but direct evidence for this hypothesis is missing. Here we show that cohesin suppresses compartments but is essential for TADs and loops, that CTCF defines their boundaries, and that WAPL and its PDS5 binding partners control the length of chromatin loops. In the absence of WAPL and PDS5 proteins, cohesin passes CTCF sites with increased frequency, forms extended chromatin loops, accumulates in axial chromosomal positions (vermicelli) and condenses chromosomes to an extent normally only seen in mitosis. These results show that cohesin has an essential genome-wide function in mediating long-range chromatin interactions and support the hypothesis that cohesin creates these by loop extrusion, until it is delayed by CTCF in a manner dependent on PDS5 proteins, or until it is released from DNA by WAPL.

genomics↗