Monomeric cohesin state revealed by live‐cell single‐molecule spectroscopy

Abstract

The cohesin complex plays an important role in the maintenance of genome stability. Cohesin is composed of four core subunits and a set of regulatory subunits that interact with the core subunits. Less is known about cohesin dynamics in live cells and on the contribution of individual subunits to the overall complex. Understanding the tethering mechanism of cohesin is still a challenge, especially because the proposed mechanisms are still not conclusive. Models proposed to describe tethering depend on either the monomeric cohesin ring or a cohesin dimer. Here, we investigate the role of cohesin dynamics and stoichiometry in live yeast cells at single-molecule resolution. We explore the effect of regulatory subunit deletion on cohesin mobility and found that depletion of different regulatory subunits has opposing effects. Finally, we show that cohesin exists mostly as a canonical monomer throughout the cell cycle, and its monomeric form is independent of its regulatory factors. Our results demonstrate that single-molecule tools have the potential to provide new insights into the cohesin mechanism of action in live cells.

Distinct and overlapping roles of STAG1 and STAG2 in cohesin localization and gene expression in embryonic stem cells

“…These results in cells parallel observations in Xenopus extracts, in which inhibition of STAG incorporation into cohesin complexes interferes with cohesin occupancy on chromatin [8]. It is also consistent with a recent report suggesting that a STAG subunit is necessary for a conformational change within the cohesin core ring, promoting its stable association with chromatin [32]. However, we do note that simultaneous depletion of STAG1 and STAG2 fails to disrupt the interaction between the core cohesin ring and CTCF, in contrast with previous findings indicating that STAG proteins are the principal interface between cohesin and CTCF [35,36].…”

“…Our results demonstrate that STAG1 and STAG2 display nearly identical distributions across the genome, despite not interacting together in a stable complex. Our finding that the STAG proteins do not physically interact corroborates similar coIP and microscopy results in mESCs and human colorectal cancer lines, and is consistent with a model where cohesin functions as a single ring, rather than as a pair of rings [8,23,25,27,32,41,42]. Several recent reports have found that STAG1 and STAG2 localize at many shared sites, but also localize to a subset of sites exclusively [23][24][25]27].…”

“…Various models of cohesin function have been proposed, some involving a single cohesin ring complex and others requiring two rings to bring a pair of distal sequences into physical proximity [30][31][32][33]. Overlapping distribution of cohesin-STAG1 and cohesin-STAG2 on the genome.…”

Hit the brakes – a new perspective on the loop extrusion mechanism of cohesin and other SMC complexes

“…2A) (Huang et al, 2005;Zhang et al, 2008). More recent structural and spectroscopic studies provide strong support that tethering involves a single copy of the cohesin complex with two distinct chromatinbinding sites (model 2) (Chapard et al, 2019;Liu et al, 2020;Xu and Yanagida, 2019). However, evidence pointing to cohesin dimerization (Eng et al, 2014(Eng et al, , 2015 needs to be reconciled with this model.…”

IRX3/5 regulate mitotic chromatid segregation and limb bud shape

“…The cohesin complex regulates embryonic development in plants and animals by pairing sister chromatids during cell division and by influencing transcription (Minina et al, 2017;Smith et al, 2014;Marsman et al, 2014;Tedeschi et al, 2013;Mouri et al, 2012;Kawauchi et al, 2009). During S phase, replicated sister chromatids are connected with one another by the monomeric ring-like cohesin complex, and this cohesion is necessary for biorientation and orderly segregation of chromosomes on the mitotic spindle (Peters and Nishiyama, 2012;Skibbens, 2008;Liu et al, 2019). Interestingly, deficiency of nipped-B-like (Nipbl), the product of which facilitates cohesin loading (Hirano, 2006), results in fin bud undergrowth and transcriptional misregulation in the mouse limb bud (Muto et al, 2014), as well as tibial deficiency that is a feature in common with human cohesinopathies (Pfeiffer and Correll, 1993) and murine Irx3/ 5 deletion (Li et al, 2014).…”