Pathways of spindle assembly.

Recent studies have revealed that, in some systems, chromatin has the ability to stabilize microtubules and organize them into bipolar spindles independently of kinetochores and centrosomes. In addition, several molecules have been identified recently that are necessary for spindle assembly; these include proteins that regulate microtubule dynamics, proteins that organize microtubule minus ends into spindle poles, and members of the kinesin superfamily that reside on the chromosome arms.