  Kinesin-8 motor proteins destabilize microtubules. Their absence during cell
division is associated with disorganized mitotic chromosome movements and
chromosome loss. Despite recent work studying effects of kinesin 8s on
microtubule dynamics, it remains unclear whether the kinesin-8 mitotic
phenotypes are consequences of their effect on microtubule dynamics, their
well-established motor activity, or additional unknown functions. To better
understand the role of kinesin-8 proteins in mitosis, we have studied the
effects of deletion of the fission-yeast kinesin-8 proteins Klp5 and Klp6 on
chromosome movements and spindle length dynamics. Aberrant microtubule-driven
kinetochore pushing movements and tripolar mitotic spindles occurred in cells
lacking Klp5 but not Klp6. Kinesin-8 deletion strains showed large fluctuations
in metaphase spindle length, suggesting a disruption of spindle length
stabilization. Comparison of our results from light microscopy with a
mathematical model suggests that kinesin-8 induced effects on microtubule
dynamics, kinetochore attachment stability, and sliding force in the spindle
can explain the aberrant chromosome movements and spindle length fluctuations
seen.
