Pds5 regulators segregate cohesion and condensation pathways in Saccharomyces cerevisiae

Abstract

Cohesins are required both for the tethering together of sister chromatids (termed cohesion) and subsequent condensation into discrete structures-processes fundamental for faithful chromosome segregation into daughter cells. Differentiating between cohesin roles in cohesion and condensation would provide an important advance in studying chromatin metabolism. Pds5 is a cohesin-associated factor that is essential for both cohesion maintenance and condensation. Recent studies revealed that ELG1 deletion suppresses the temperature sensitivity of pds5 mutant cells. However, the mechanisms through which Elg1 may regulate cohesion and condensation remain unknown. Here, we report that ELG1 deletion from pds5-1 mutant cells results in a significant rescue of cohesion, but not condensation, defects. Based on evidence that Elg1 unloads the DNA replication clamp PCNA from DNA, we tested whether PCNA overexpression would similarly rescue pds5-1 mutant cell cohesion defects. The results indeed reveal that elevated levels of PCNA rescue pds5-1 temperature sensitivity and cohesion defects, but do not rescue pds5-1 mutant cell condensation defects. In contrast, RAD61 deletion rescues the condensation defect, but importantly, neither the temperature sensitivity nor cohesion defects exhibited by pds5-1 mutant cells. In combination, these findings reveal that cohesion and condensation are separable pathways and regulated in nonredundant mechanisms. These results are discussed in terms of a new model through which cohesion and condensation are spatially regulated.

Of Rings and Rods: Regulating Cohesin Entrapment of DNA to Generate Intra- and Intermolecular Tethers

“…Identical results were obtained during characterization of mcd1-Q266Q mutant cells [56]. Importantly, chromatin-retained cohesins in pds5 -inactivated cells retain their acetylation state (a modification that occurs only during S phase), negating arguments that the detected cohesins involved newly loaded (i.e., during mitosis) complexes [33]. This reemerging model of cohesion establishment—that cohesins stably deposited onto each sister chromatid are subsequently converted to a tethering-competent, higher-order structure [57]—suggests that sister chromatid tethering requires multiple transition states that are likely regulated by both cohesin ATP hydrolysis and Eco1/Ctf7-dependent acetylation.…”

“…lend a cautionary tale to a “one size fits all” notion of cohesin’s structural endpoint? Importantly, cohesin functions are demonstrably separable through specific regulatory factors that include ESCO1,2, ELG1, PCNA, Rad61/WAPL, CTCF, and Scc3/SA1,2 (Fig 3) [25–33]. If these regulatory factors produce cohesin subsets of dedicated and nonoverlapping function (including distinct binding partners and cell cycle specificities), then these cohesin “changlings” may exhibit unique endpoint conformations.…”

“…In contrast, the single ring around two sister chromatids model requires that separation of previously tethered sisters must occur through cohesin release from DNA. When this prediction was tested directly, mitotic inactivation of cohesion (using a temperature-sensitive Pds5 allele) resulted in sister separation despite nearly full retention of chromatin-bound cohesin [33,55]. Identical results were obtained during characterization of mcd1-Q266Q mutant cells [56].…”

The Opposing Actions of Arabidopsis CHROMOSOME TRANSMISSION FIDELITY7 and WINGS APART-LIKE1 and 2 Differ in Mitotic and Meiotic Cells

“…In yeast, RAD51 deletion has been shown to suppress pds5 and ctf7 condensation defects (Tong and Skibbens, 2015). This led to the suggestion that Pds5 and Ctf7/ Eco1 promote condensation through a common WAPL-mediated mechanism regulated by Rad51 (Tong and Skibbens, 2015).…”

“…In yeast, RAD51 deletion has been shown to suppress pds5 and ctf7 condensation defects (Tong and Skibbens, 2015). This led to the suggestion that Pds5 and Ctf7/ Eco1 promote condensation through a common WAPL-mediated mechanism regulated by Rad51 (Tong and Skibbens, 2015). Mouse cells depleted for Wapl contain partially condensed chromosomes with regions of hypercondensed heterochromatin (Tedeschi et al, 2013).…”