Drosophila kinesin-8 stabilises kinetochore-microtubule interaction

Kinesin-8 is required for proper chromosome alignment in a variety of animal and yeast cell types. However, how this conserved motor protein controls chromosome alignment remains unclear, as multiple biochemical activities, including inconsistent ones between studies, have been identified for this motor family. Here, we show that Drosophila kinesin-8 Klp67A possesses both microtubule (MT) plus-end-stabilising and -destabilising activities in addition to commonly observed MT plus-end-directed motility and tubulin-binding activity in vitro, and is required for stable kinetochore-MT attachment during prometaphase in vivo. In the absence of kinesin-8Klp67A, abnormally-long MTs interact in an “end-on” fashion with kinetochores at normal frequency. However, the interaction was not stable and, once-attached, MTs were frequently detached. This phenotype was rescued by ectopic expression of MT plus-end-stabilising factor CLASP, but not by artificial shortening of MTs. These results suggest that MT-stabilising activity of kinesin-8Klp67A is critical for stable kinetochore-MT attachment.