Pericentromeric Sister Chromatid Cohesion Promotes Kinetochore Biorientation

Abstract

Accurate chromosome segregation depends on sister kinetochores making bioriented attachments to microtubules from opposite poles. An essential regulator of biorientation is the Ipl1/Aurora B protein kinase that destabilizes improper microtubule-kinetochore attachments. To identify additional biorientation pathways, we performed a systematic genetic analysis between the ipl1-321 allele and all nonessential budding yeast genes. One of the mutants, mcm21Delta, precociously separates pericentromeres and this is associated with a defect in the binding of the Scc2 cohesin-loading factor at the centromere. Strikingly, Mcm21 becomes essential for biorientation when Ipl1 function is reduced, and this appears to be related to its role in pericentromeric cohesion. When pericentromeres are artificially tethered, Mcm21 is no longer needed for biorientation despite decreased Ipl1 activity. Taken together, these data reveal a specific role for pericentromeric linkage in ensuring kinetochore biorientation.

The Composition, Functions, and Regulation of the Budding Yeast Kinetochore

“…Cohesin would therefore encircle a single chromatid rather than sisters in this region, resolving the apparent "cohesin" paradox where the highest levels of cohesin reside in the areas that are physically split at metaphase. At least one function of pericentric cohesion is to facilitate kinetochore biorientation by resisting the pulling forces of microtubules and/or by promoting the architecture of sister kinetochores (Eckert et al 2007;Fernius and Marston 2009;Ng et al 2009;Bloom and Joglekar 2010). Consistent with this, the geometry and elasticity of the pericentromere and inner kinetochore can change in response to alterations in microtubule dynamics (Haase et al 2012;Stephens et al 2013).…”

“…These properties are regulated by the Bub1 and Sgo1 proteins as well as various chromatin-remodeling complexes (Haase et al 2012;Verdaasdonk et al 2012). While heterochromatin recruits pericentric cohesin in some organisms (Bernard et al 2001;Fukagawa et al 2004), components of the kinetochore itself direct cohesion enrichment in budding yeast (Megee et al 1999;Tanaka et al 1999;Weber et al 2004;Eckert et al 2007;Fernius and Marston 2009;Ng et al 2009;Fernius et al 2013).…”

“…Consistent with this, cohesin is highly enriched in a 50-kb domain around yeast centromeres, presumably to resist the pulling forces of microtubules (Megee et al 1999;Tanaka et al 1999;Glynn et al 2004). The kinetochore is required to recruit pericentromeric cohesin, and the COMA subcomplex has been specifically implicated in this process (Tanaka et al 1999;Weber et al 2004;Eckert et al 2007;Fernius and Marston 2009;Ng et al 2009;Fernius et al 2013). However, the details of how cohesin spreads from kinetochores to a large domain around the centromere are still unknown.…”

Kinetochore Function and Chromosome Segregation Rely on Critical Residues in Histones H3 and H4 in Budding Yeast

“…We isolated mutants that require the full activity of the Ipl1/Aurora B protein kinase for viability. To do this, we used a previously characterized doxycycline-repressible degron allele, deg-ipl1, that targets the protein for degradation by the proteasome (Ng et al 2009). Although IPL1 is essential, doxycycline addition does not severely inhibit the growth of deg-ipl1 cells ( Figure 1C), indicating that these cells retain enough Ipl1 function to support viability.…”

“…Although IPL1 is essential, doxycycline addition does not severely inhibit the growth of deg-ipl1 cells ( Figure 1C), indicating that these cells retain enough Ipl1 function to support viability. However, deg-ipl1 is lethal when combined with other nonessential mutants such as the mcm21 kinetochore mutant, indicating that it is a hypomorphic allele (Ng et al 2009). We therefore introduced each alanine substitution mutation in H3 and H4 into a deg-ipl1 strain containing a deletion of the secondary copy of H3 and H4, hht1-hhf1Δ.…”