The fission yeast Schizosaccharomyces pombe divides through constriction of an actomyosin-based contractile ring followed by formation and degradation of a medial septum. Formation of an organized septin ring is also important for the completion of S. pombe cell division and this event relies on the production of Mid2p. mid2 + mRNA and protein accumulate in mitosis. Recent microarray analyses identified mid2 + as a target of the Ace2p transcription factor, and ace2 + as a target of the Sep1p transcription factor. In this study, we find that Mid2p production is controlled by Ace2p functioning downstream of Sep1p. Consequently, both Sep1p and Ace2p are required for septin ring assembly and genetic analyses indicate that septin rings function in parallel with other Ace2p targets to achieve efficient cell division. Conversely, forced overproduction of Sep1p or Ace2p prevents septin ring disassembly. We find that Ace2p levels peak during anaphase and Ace2p is post-translationally modified by phosphorylation and ubiquitylation. Ace2p localizes symmetrically to dividing nuclei and functions independently of the septation initiation network.

The periodicity of CDKs (cyclin-dependent kinases) regulates most cell cycle transitions including cytokinesis. High Cdk1 activity promotes cytoskeletal rearrangements necessary for cell division while at the same time ensuring that cytokinesis does not begin before the separation of sister chromatids during anaphase. The conserved Cdc14 (cell division cycle 14)-family of phosphatases reverses Cdk phosphorylation events and therefore Cdc14 phosphatases promote the process of cytokinesis. Here, we review the elucidated roles of Cdc14 phosphatases in cytokinesis and the current outstanding questions regarding their function in this process.