A coordinated kinase and phosphatase network regulates Stu2 recruitment to yeast kinetochores

Cells coordinate diverse events at anaphase onset, including separase activation, cohesin cleavage, chromosome separation, and spindle reorganization. Regulation of the XMAP215 family member and microtubule polymerase, Stu2, at the metaphase-anaphase transition determines a redistribution from kinetochores to spindle microtubules. We show that cells modulate Stu2 kinetochore-microtubule localization by Polo-like kinase1/Cdc5-mediated phosphorylation of T866, near the Stu2 C-terminus, thereby promoting dissociation from the kinetochore Ndc80 complex. Cdk/Cdc28 likely primes Cdc5:Stu2 interaction. Cdc28 activity is also required for Stu2 nuclear import. PP2A^Cdc55 actively opposes Cdc5 activity on Stu2^T866 during metaphase. This counter-regulation allows for switch-like redistribution of Stu2^pT866 at anaphase onset when separase inhibits PP2A^Cdc55. Blocking Stu2^T866 phosphorylation disrupts anaphase spindle progression, and we infer that PP2A^Cdc55 regulates the mitotic spindle by dephosphorylating multiple MAPs, including Stu2. These data support a model in which increased phosphorylation at anaphase onset results from phosphatase inhibition and point to a larger regulatory network that facilitates rapid cytoskeletal modulation required for anaphase spindle function.