The DNA-binding protein CST associates with the cohesin complex and promotes chromosome cohesion

Abstract

Sister chromatid cohesion (SCC), the pairing of sister chromatids after DNA replication until mitosis, is established by loading of the cohesin complex on newly replicated chromatids. Cohesin must then be maintained until mitosis to prevent segregation defects and aneuploidy. However, how SCC is established and maintained until mitosis remains incompletely understood, and emerging evidence suggests that replication stress may lead to premature SCC loss. Here, we report that the ssDNA-binding protein CTC1-STN1-TEN1 (CST) aids in SCC. CST primarily functions in telomere length regulation but also has known roles in replication restart and DNA repair. After depletion of CST subunits, we observed an increase in the complete loss of SCC. In addition, we determined that CST associates with the cohesin complex. Unexpectedly, we did not find evidence of altered cohesin loading or mitotic progression in the absence of CST; however, we did find that treatment with various replication inhibitors increased the association between CST and cohesin. Because replication stress was recently shown to induce SCC loss, we hypothesized that CST may be required to maintain or remodel SCC after DNA replication fork stalling. In agreement with this idea, SCC loss was greatly increased in CST-depleted cells after exogenous replication stress. Based on our findings, we propose that CST aids in the maintenance of SCC at stalled replication forks to prevent premature cohesion loss.

Microsatellite break-induced replication generates highly mutagenized extrachromosomal circular DNAs

“…In S. cerevisiae , DSBs are repaired by long tract gene conversion (LTGC) and synthesis-dependent strand annealing (SDSA) if both ends have proximal homology on the sister chromatid (54,55,157), whereas mutagenic BIR from a single-ended DSB (seDSB) can occur if a parental strand at the DSB becomes ligated to a nascent DNA strand. Alternatively, bidirectional BIR can occur if the ends do not contain proximal (∼1-2 kb) homology on the donor DNA (131,157,158), or when the second end of the break is not captured (131,159,160) due to a converging fork, the absence of proteins that promote strand annealing (161) or due to singular structures of DNA or chromatin (103,162–173).…”

The Interplay of Cohesin and the Replisome at Processive and Stressed DNA Replication Forks

“…Possibly, the removal of cohesin at stalled replication forks comes at the cost of reduced sister chromatid cohesion. Interestingly, the ssDNA binding protein complex CTC1-STN1-TEN1 (CST) was recently shown to interact with cohesin and proposed to preserve functional cohesion in conditions of replication stress [ 191 ].…”

Dysfunction of telomeric Cdc13-Stn1-Ten1 simultaneously activates the DNA damage and spindle checkpoints

“…Importantly, hCST subunits were found by immunofluorescence to localize at only a fraction of telomeres and the hypersensitivity of mutants of hCST to DNA damaging agents indicated a function in ensuring genome-wide replication restart in response to DNA replication stress and replication fork stalling [20,[25][26][27]. Finally, hCST has a role in the initiation of DNA replication in association with MCM proteins [28] and also physically associates with the cohesin complex, perhaps to prevent premature cohesion loss between chromosomes at stalled replication forks [29]. Recently too, A. thaliana TEN1 was shown to act as a heat-shock-induced molecular chaperone, potentially protecting CTC1 from forming aggregates [30].…”