Most cells divide by assembling a contractile actomyosin cytokinetic ring (CR) that is anchored to the plasma membrane (PM). Proper endoplasmic reticulum (ER) and PM contact sites, as well as stable CR–PM attachments, are essential for symmetric cell division and, in turn, depend on membrane lipid composition. In Schizosaccharomyces pombe, the phosphatidylinositol 4-phosphate 5-kinase Its3 synthesises one of the main lipid PM components, phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2]. However, the regulation of Its3 remains unclear. Here (Willet et al., 2024), Gould and colleagues use proximity-based biotinylation to identify proteins associated with Its3 and its partner Opy1, discovering Duc1. The authors observe that Duc1 localises to the cell cortex but is excluded from the medial region during mitosis, relocating to the cell tips – unlike Opy1 and Its3, which localise uniformly. Additionally, Duc1 binds to the ER–PM contact site proteins Scs2 and Scs22, and in scs2Δ scs22Δ cells Duc1 localises along the entire PM, suggesting that these proteins exclude Duc1 from the division site during mitosis. Furthermore, duc1Δ cells show reduced Its3 and PI(4,5)P2 levels in the lateral PM, whereas overproduction of Duc1 mislocalises Opy1. Both deletion and overexpression of duc1 lead to misaligned CRs and division asymmetries. Taken together, these findings suggest that Duc1 has a role in lipid homeostasis and in proper CR–PM anchoring, which is crucial for symmetric cell division in S. pombe.
