👤 Dannel McCollum

Cytokinesis in the fission yeast Schizosaccharomyces pombe is regulated by a signaling pathway termed the septation initiation network (SIN). The SIN is essential for initiation of actomyosin ring constriction and septum formation. In a screen to search for mutations that can rescue the sid2-250 SIN mutant, we obtained scw1-18. Both the scw1-18 mutant and the scw1 deletion mutant (scw1Delta mutant), have defects in cell separation. Both the scw1-18 and scw1Delta mutations rescue the growth defects of not just the sid2-250 mutant but also the other temperature-sensitive SIN mutants. Other cytokinesis mutants, such as those defective for actomyosin ring formation, are not rescued by scw1Delta. scw1Delta does not seem to rescue the SIN by restoring SIN signaling defects. However, scw1Delta may function downstream of the SIN to promote septum formation, since scw1Delta can rescue the septum formation defects of the cps1-191beta-1,3-glucan synthase mutant, which is required for synthesis of the primary septum. Show less

Schizosaccharomyces pombe divides by medial fission through the use of an actomyosin-based contractile ring. A division septum is formed centripetally, concomitant with ring constriction. Although several genes essential for cytokinesis have been described previously, enzymes that participate in the assembly of the division septum have not been identified. Here we describe a temperature-sensitive mutation, drc1-191, that prevents division septum assembly and causes mutant cells to arrest with a stable actomyosin ring. Unlike the previously characterized cytokinesis mutants, which undergo multiple mitotic cycles, drc1-191 is the first cytokinesis mutant that arrests with two interphase nuclei. Interestingly, unlike drc1-191, drc1-null mutants proceed through multiple mitotic cycles, leading to the formation of large cells with many nuclei. drc1 is allelic to cps1, which encodes a 1,3-beta-glucan synthase subunit. We conclude that Drc1p/Cps1p is not required for cell elongation and cell growth, but plays an essential role in assembly of the division septum. Furthermore, it appears that constriction of the actomyosin ring might depend on assembly of the division septum. We discuss possible mechanisms that account for the differences in the phenotypes of the drc1-191 and the drc1-null mutants and also reflect the potential links between Drc1p and other cytokinesis regulators. Show less