Mitotic phosphatases: from entry guards to exit guides.

While the importance of protein kinases for the spatial and temporal control of mitotic events has long been recognized, mitotic phosphatases have only recently come into the limelight. It is now well established that protein phosphatases counteract mitotic kinases, so contributing to the generation of switch-like responses at mitotic stage transitions. In addition, the timely dephosphorylation of mitotic phosphoproteins by tightly regulated phosphatases is required for the assembly and stability of the mitotic spindle, the initiation of anaphase, and exit from mitosis. Mitotic phosphatases also emerge as effectors of the DNA damage and spindle assembly checkpoints. These new findings show that protein phosphatases regulate every step of mitosis and provide novel insights into the dynamic and versatile nature of mitotic phosphoregulation.