The dynamics of kinetochore-attached microtubules govern the metaphase need for kinesin-5 in human cells
Kinetochore-microtubule stability governs the metaphase requirement for Eg5
A. Sophia Gayek1 and Ryoma Ohi1,
Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232
Kerry Bloom, Monitoring Editor
Submitted March 3, 2014, Revised April 28, 2014, Accepted May 1, 2014.
Abstract
The mitotic spindle is a bipolar, microtubule (MT)-based cellular machine that segregates the duplicated genome into two daughter cells. The kinesin-5 Eg5 establishes the bipolar geometry of the mitotic spindle, but previous work in mammalian cells has suggested that this motor is unimportant for the maintenance of spindle bipolarity. Although it is known that Kif15, a second mitotic kinesin, enforces spindle bipolarity in the absence of Eg5, it remains poorly studied how Kif15 functions in this capacity and/or whether other biochemical or physical properties of the spindle promote its bipolarity. Here we report that not all human cell lines can efficiently maintain bipolarity without Eg5, despite expressing Kif15. We show that the stability of chromosome-attached kinetochore-MTs (K-MTs) is important for bipolar spindle maintenance without Eg5. Cells that efficiently maintain bipolar spindles without Eg5 have more stable K-MTs than those which collapse without Eg5. Consistent with this observation, artificial destabilization of K-MTs promotes spindle collapse without Eg5, while stabilizing K-MTs improves bipolar spindle maintenance without Eg5. Our findings suggest either that rapid K-MT turnover pulls poles inward, or that slow K-MT turnover allows for greater resistance to inward-directed forces.