A Genetic Screen for Functional Partners of Condensin in Fission Yeast

Abstract

Mitotic chromosome condensation is a prerequisite for the accurate segregation of chromosomes during cell division, and the conserved condensin complex a central player of this process. However, how condensin binds chromatin and shapes mitotic chromosomes remain poorly understood. Recent genome-wide binding studies showing that in most species condensin is enriched near highly expressed genes suggest a conserved link between condensin occupancy and high transcription rates. To gain insight into the mechanisms of condensin binding and mitotic chromosome condensation, we searched for factors that collaborate with condensin through a synthetic lethal genetic screen in the fission yeast Schizosaccharomyces pombe. We isolated novel mutations affecting condensin, as well as mutations in four genes not previously implicated in mitotic chromosome condensation in fission yeast. These mutations cause chromosome segregation defects similar to those provoked by defects in condensation. We also identified a suppressor of the cut3-477 condensin mutation, which largely rescued chromosome segregation during anaphase. Remarkably, of the five genes identified in this study, four encode transcription co-factors. Our results therefore provide strong additional evidence for a functional connection between chromosome condensation and transcription.

Perichromosomal protein Ki67 supports mitotic chromosome architecture

“…; Robellet et al . ; Nikalayevich & Ohkura ). The relevance of these proteins and Ki67 is also worth examining.…”

“…; Robellet et al . ; Nikalayevich & Ohkura ). Although recent studies have shown that mitotic chromosome‐like structures can be reconstituted in vitro with only six defined factors (Shintomi et al .…”

“…The significant contributions of condensin complexes and topoisomerase IIa (TopoIIa) to the assembly of mitotic chromosomes have been demonstrated in various biological and experimental contexts (Swedlow & Hirano 2003;Hirano 2012). On the contrary, certain cells reportedly manage to assemble mitotic chromosomes with a seemingly normal condensation state-albeit with imperfect shape-even in the absence of condensins or TopoIIa, which has prompted researchers to seek additional chromosome condensation factors (Vagnarelli et al 2006;Petrova et al 2013;Heriche et al 2014;Robellet et al 2014;Nikalayevich & Ohkura 2015). Although recent studies have shown that mitotic chromosome-like structures can be reconstituted in vitro with only six defined factors (Shintomi et al 2015), their relevance to authentic chromosomes formed in vivo remains to be verified.…”

A conserved role of the RSC chromatin remodeler in the establishment of nucleosome-depleted regions

“…Although these phenotypes may result from the reduced expression of specific genes, a recent study rather points to a direct role of RSC and nucleosome eviction in condensin loading and chromosome condensation (Toselli-Mollereau et al 2016). A genetic screen for functional partners of condensin in fission yeast (synthetic lethality with cut3 - 477 that encodes a condensin ATPase subunit) identified alleles of arp9 and snf21 that both showed high frequency of chromatin bridges in anaphase (Robellet et al 2014). Further analyses revealed the preferred localization of condensin at, or near NDR and that increased nucleosome occupancy upon RSC downregulation is sufficient to decrease condensin binding.…”

Are all repeats created equal? Understanding DNA repeats at an individual level

“…However, among individual otr3L repeats there is no apparent bias in Cut3 distribution, suggesting additional factors may be required to establish position-dependent heterochromatin organizations. Cohesins and other chromatin remodeling complexes are possible candidates to control the position effect within the peri-centromeric repeat array (Mizuguchi et al, 2014; Robellet et al, 2014). …”