Sgo1 Regulates Both Condensin and Ipl1/Aurora B to Promote Chromosome Biorientation

Abstract

Correct chromosome segregation is essential in order to prevent aneuploidy. To segregate sister chromatids equally to daughter cells, the sisters must attach to microtubules emanating from opposite spindle poles. This so-called biorientation manifests itself by increased tension and conformational changes across kinetochores and pericentric chromatin. Tensionless attachments are dissolved by the activity of the conserved mitotic kinase Aurora B/Ipl1, thereby promoting the formation of correctly attached chromosomes. Recruitment of the conserved centromeric protein shugoshin is essential for biorientation, but its exact role has been enigmatic. Here, we identify a novel function of shugoshin (Sgo1 in budding yeast) that together with the protein phosphatase PP2A-Rts1 ensures localization of condensin to the centromeric chromatin in yeast Saccharomyces cerevisiae. Failure to recruit condensin results in an abnormal conformation of the pericentric region and impairs the correction of tensionless chromosome attachments. Moreover, we found that shugoshin is required for maintaining Aurora B/Ipl1 localization on kinetochores during metaphase. Thus, shugoshin has a dual function in promoting biorientation in budding yeast: first, by its ability to facilitate condensin recruitment it modulates the conformation of the pericentric chromatin. Second, shugoshin contributes to the maintenance of Aurora B/Ipl1 at the kinetochore during gradual establishment of bipolarity in budding yeast mitosis. Our findings identify shugoshin as a versatile molecular adaptor that governs chromosome biorientation.

Premature Silencing of the Spindle Assembly Checkpoint Is Prevented by the Bub1-H2A-Sgo1-PP2A Axis in Saccharomyces cerevisiae

“…Thus, we first examined the sensitivity of rts1D mutants to CIK1-CC overexpression. rts1D cells harboring P GAL CIK1-CC plasmids grew very poorly on galactose plates ( Figure 4A), which is consistent with a previous observation (Peplowska et al 2014). Moreover, after 6-hr incubation in galactose medium, 62% of rts1D cells with P GAL CIK1-CC plasmids were inviable, whereas only 8% of rts1D cells with a vector lost viability.…”

“…However, the observation that the tension sensing by Ipl1 is independent of the centromere localization of Ipl1 complex argues against this possibility (Campbell and Desai 2013). Consistently, overexpression of the Ipl1 cofactor SLI15 restores centromere Ipl1 localization in sgo1D mutants, but this fails to suppress sgo1D's sensitivity to CIK1-CC overexpression (Peplowska et al 2014). Here, we further showed that sgo1D mutation alleviated the anaphase entry delay in the phospho-mimetic mutant dam1-3D.…”

“…Previous studies indicate that Sgo1 recruits Ipl1/Aurora B kinase complex to centromeres Peplowska et al 2014). Because Ipl1 kinase prevents SAC silencing in response to tension defects (Biggins and Murray 2001;Jin et al 2012;Jin and Wang 2013), one speculation is that Sgo1 prevents SAC silencing through Ipl1 kinase.…”

“…Thus, we mutated this motif to four alanine residues, generating a sgo1-4A plasmid. Previous works define the PP2A-binding domain in Sgo1 as well, and sgo1-N51I mutation abolishes this interaction (Xu et al 2009;Peplowska et al 2014). We also generated a sgo1-N51I plasmid.…”

“…Centromere-localized Sgo1 recruits PP2A Rts1 , condensin, and Ipl1 kinase complex to the centromere region (Riedel et al 2006;Peplowska et al 2014;Verzijlbergen et al 2014). Although we found that Ipl1 is required to prevent premature SAC silencing in response to tension defects (Jin and Wang 2013), previous work shows that the centromere localization of Ipl1 is dispensable for this function (Campbell and Desai 2013).…”