Cohesin Can Remain Associated with Chromosomes during DNA Replication

James D.P Rhodes,Judith H.I Haarhuis,Jonathan B Grimm,Benjamin D Rowland,Luke D Lavis,Kim A Nasmyth

doi:10.1016/j.celrep.2017.08.092

Abstract

SummaryTo ensure disjunction to opposite poles during anaphase, sister chromatids must be held together following DNA replication. This is mediated by cohesin, which is thought to entrap sister DNAs inside a tripartite ring composed of its Smc and kleisin (Scc1) subunits. How such structures are created during S phase is poorly understood, in particular whether they are derived from complexes that had entrapped DNAs prior to replication. To address this, we used selective photobleaching to determine whether cohesin associated with chromatin in G1 persists in situ after replication. We developed a non-fluorescent HaloTag ligand to discriminate the fluorescence recovery signal from labeling of newly synthesized Halo-tagged Scc1 protein (pulse-chase or pcFRAP). In cells where cohesin turnover is inactivated by deletion of WAPL, Scc1 can remain associated with chromatin throughout S phase. These findings suggest that cohesion might be generated by cohesin that is already bound to un-replicated DNA.

Highlights

The equal distribution of genetic material at cell division requires attachment of sister kinetochores to microtubules emanating from opposite sides of the cell, a process that depends on cohesion between sister chromatids
Sister chromatid cohesion is mediated by the cohesin complex, the core of which is a tripartite ring created by the binding of N- and C-terminal domains of a kleisin subunit Scc1 (Rad21) to the ATPase domains at the apices of a V-shaped Smc1/3 heterodimer (Gruber et al, 2003; Haering et al, 2002)
Cohesion is thought to depend on entrapment of sister DNAs inside cohesin rings, while topologically associating domains (TADs) have been postulated to arise through the extrusion of loops of chromatin fibers through these rings, a hypothesis known as loop extrusion (Alipour and Marko, 2012; Fudenberg et al, 2016; Nasmyth, 2001; Sanborn et al, 2015)

Summary

Introduction

The equal distribution of genetic material at cell division requires attachment of sister kinetochores to microtubules emanating from opposite sides of the cell, a process that depends on cohesion between sister chromatids. Loading of cohesin onto chromosomes begins in telophase (Sumara et al, 2000) and depends on a complex of Scc (Nipbl) and Scc (Mau2) (Ciosk et al, 2000). From this point until the onset of DNA replication, the dynamics of cohesin’s association with chromatin is determined by the rate of loading catalyzed by Scc and the rate of release catalyzed by Wapl and Pds (Kueng et al, 2006). During G1, these two processes create a steady state where about 50% of cohesin is associated with chromatin with a residence time of about 20 min (Gerlich et al, 2006; Hansen et al, 2017)

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