Cytokinesis is the highly regulated process that physically separates daughter and mother cells in late mitosis. In Saccharomyces cerevisiae, cytokinesis involves constriction of an actomyosin ring and formation of a chitin-rich primary septum, which are processes that must be coordinated with mitotic exit to ensure that cytokinesis only occurs after chromosome segregation. Gislene Pereira and colleagues now report that the mitotic-exit network (MEN), the signalling pathway that drives mitotic exit, directly regulates cytokinesis by targeting components that are involved in septum formation to the bud-neck region (p. ). The authors show, for example, that Cyk3, Inn1 and Chs2 – three regulatory components of the primary septum – fail to localise normally to the bud neck in MEN-deficient mutants that have been forced to exit mitosis through inactivation of the mitotic cyclin-dependent kinase Cdk1. Consistent with this observation, ultrastructural studies indicate that septum formation in MEN-deficient mutants is abnormal. On the basis of these and other results, the authors propose that the MEN coordinates cytokinesis in budding yeast by bringing together components involved in actomyosin-ring contraction and septum formation after mitotic exit.
