Not Just for Pulling Chromosomes: The Role of Kinetochore-Microtubules in Enforcing Bipolarity of the Human Mitotic Spindle
Gayek, Anna Sophia
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2016-03-30
Abstract
Two processes influence the success of mitosis, the process by which eukaryotic cells divide their replicated genome into two new daughter cells. First, the cell must build a bipolar array of microtubules called the mitotic spindle, which is accomplished by microtubule sliding by the Kinesin-5 Eg5; second, a subset of those microtubules, called kinetochore-microtubules (K-MTs), must attach correctly to each chromosome. The stability of these K-MT attachments to the chromosome influences whether chromosomes will segregate correctly in anaphase, but an influence of K-MT stability on the ability of cells to build or maintain bipolar spindles had not been recognized. Here we show that human cell lines with high K-MT stability are better able to maintain bipolar spindles when Eg5 is inhibited compared to cell lines with low K-MT stability. Artificially stabilizing K-MTs promoted bipolarity maintenance, while destabilizing K-MTs undermined the maintenance of bipolarity. In addition, inhibition of the mitotic master-regulator cyclin-dependent kinase-1 (CDK-1) in the G2 phase of the cell cycle stabilized K-MTs after CDK-1 inhibition was relieved, which promoted bipolar spindle maintenance without Eg5 but undermined mitotic fidelity. These results indicate that the dynamics of K-MTs play a previously unappreciated role in determining the overall geometry of the mitotic spindle.