DISTINCT ROLES OF PP1 AND PP2A-LIKE PHOSPHATASES IN CONTROL OF MICROTUBULE DYNAMICS DURING MITOSIS

Assembly of a mitotic spindle requires the accurate regulation of micr otubule dynamics which is accomplished, at least in part, by phosphory lation-dephosphorylation reactions. Here we have investigated the role of serine-threonine phosphatases in the control of microtubule dynami cs using specific inhibitors in Xenopus egg extracts. Type 2A phosphat ases are required to maintain the short steady-state length of microtu bules in mitosis by regulating the level of microtubule catastrophes, in part by controlling the the microtubule-destabilizing activity and phosphorylation of Op18/stathmin. Type 1 phosphatases are only require d for control of microtubule dynamics during the transitions into and out of mitosis. Thus, although both type 2A and type 1 phosphatases ar e involved in the regulation of microtubule dynamics, they have distin ct, non-overlapping roles.