The fission yeast cytokinetic ring component Fic1 promotes septum formation

Abstract

InSchizosaccharomyces pombeseptum formation is coordinated with cytokinetic ring constriction but the mechanisms linking these events are unclear. In this study, we explored the role of the cytokinetic ring component Fic1, first identified by its interaction with the F-BAR protein Cdc15, in septum formation. We found that thefic1phospho-ablating mutant,fic1-2A, is a gain-of-function allele that suppressesmyo2-E1, the temperature-sensitive allele of the essential type-II myosin,myo2. This suppression is achieved by the promotion of septum formation and required Fic1’s interaction with the F-BAR proteins Cdc15 and Imp2. Additionally, we found that Fic1 interacts with Cyk3 and that this interaction was likewise required for Fic1’s role in septum formation. Fic1, Cdc15, Imp2, and Cyk3 are the orthologs of theSaccharomyces cerevisiaeingression progression complex, which stimulates the chitin synthase Chs2 to promote primary septum formation. However, our findings indicate that Fic1 promotes septum formation and cell abscission independently of theS. pombeChs2 ortholog. Thus, while similar complexes exist in the two yeasts that each promote septation, they appear to have different downstream effectors.