Without Ncd (middle), K-fibers don't focus; but without dynein (right), they are not transported toward centrosomes.
Spindle microtubules emanate from the centrosomes or, as long thick ropes called K-fibers, from kinetochores. Previous work showed that two minus end–directed molecular motors—dynein and Ncd—are required to intertwine the two types of microtubules and bring them into the familiar diamond shape. In cells lacking either motor, the microtubules splay apart, failing to gather their minus ends near the centrosomes.
Using video microscopy with GFP-labeled components, FRAP, and RNAi, the team found that the motors have some functional redundancy but also have a preference for jobs. Loss of Ncd results primarily in a loss of K-fiber focusing, whereas loss of dynein compromises the...
