| During mitosis, kinetochores on each chromatid attach to microtubules emanating from two spindle poles. Errors in either kinetochore-microtubule attachment or in mitotic spindle assembly are deleterious to proper segregation of chromosomes during mitosis, and can result in debilitating diseases and cancers. This work will focus on a pathway involved in the correction of a specific type of incorrect microtubule-kinetochore attachment, and will also address the function of a related protein in the assembly of bipolar spindles.;Merotelic attachment is one in which a single kinetochore is attached to microtubules emanating from both poles. This incorrect attachment must be corrected before anaphase, or it can result in aneuploidy in the resulting daughter cells. We find that Aurora B kinase is enriched at points of merotelic attachment, and that its activity recruits and regulates the microtubule depolymerase MCAK at these sites as well. This is the first work to outline a merotelic resolution pathway.;While MCAK is recruited to merotelic attachments, it is inhibited at these sites by Aurora B phosphorylation. We find that another related depolymerase, Kif2a, is similarly inhibited by Aurora B phosphorylation. We find that the protein ICIS is able to stimulate Kif2a that has been phosphorylated and inhibited by Aurora B, suggesting a new method of regulation of microtubule depolymerases. ICIS, while stimulating Kif2a, also binds Aurora B and its activators microtubules, INCENP and TD-60. We propose a model where ICIS acts as a scaffold to bring together positive and negative regulators of microtubule depolymerases to allow tight spatial and temporal regulation of their activities.;Finally, we have found two Aurora phosphorylation sites on Kif2a, which are localized to different regions on the mitotic spindle, suggesting differential regulation of two sites by the same kinase. We also uncover a new function of Kif2a in the focusing of spindle microtubules towards chromatin. We propose a model in which asymmetric regulation of Kif2a activity gives rise to this focusing of microtubule asters. |
