Fission yeast Duc1 links to ER-PM contact sites and influences PM lipid composition and cytokinetic ring anchoring.

Cytokinesis is the final stage of the cell cycle that results in the physical separation of daughter cells. To accomplish cytokinesis, many organisms build an actin- and myosin-based cytokinetic ring (CR) anchored to the plasma membrane (PM). Defects in CR-PM anchoring can arise when the PM lipid, phosphatidylinositol-4,5- bisphosphate [PI(4,5)P2], is depleted. In Schizosaccharomyces pombe, reduced PM PI(4,5)P2 results in a CR that cannot maintain its medial position and slides toward one cell end, resulting in two differently sized daughter cells. S. pombe PM PI(4,5)P2 is synthesized by the PI5-kinase Its3, but what regulates this enzyme to maintain appropriate PM PI(4,5)P2 levels is not known in S. pombe. To identify Its3 regulators, we used proximity-based biotinylation and the uncharacterized protein Duc1 was specifically detected. We discovered that Duc1 decorates the PM except at the cell division site and that its unique localization pattern is dictated by binding to the ER-PM contact site proteins, Scs2 and Scs22. Our evidence suggests Duc1 also binds PI(4,5)P2 and helps enrich Its3 at the lateral PM, thereby promoting PM PI(4,5)P2 synthesis and robust CR-PM anchoring.