Involvement of complex sphingolipids and phosphatidylserine in endosomal trafficking in yeast S accharomyces cerevisiae

Summary Sphingolipids play critical roles in many physiologically important events in the yeast S accharomyces cerevisiae . In this study, we found that csg2 Δ mutant cells defective in the synthesis of mannosylinositol phosphorylceramide exhibited abnormal intracellular accumulation of an exocytic v‐ SNARE , S nc1, under phosphatidylserine synthase gene ( PSS1 )‐repressive conditions, although in wild‐type cells, S nc1 was known to cycle between plasma membranes and the late G olgi via post‐ G olgi endosomes. The mislocalized S nc1 was co‐localized with an endocytic marker dye, FM 4‐64, upon labelling for a short time. The abnormal distribution of Sn c1 was suppressed by deletion of GYP2 encoding a GTP ase‐activating protein that negatively regulates endosomal vesicular trafficking, or expression of GTP ‐restricted form of Y pt32 GTP ase. Furthermore, an endocytosis‐deficient mutant of S nc1 was localized to plasma membranes in PSS1 ‐ repressed csg2 Δ mutant cells as well as wild‐type cells. Thus, the PSS1 ‐ repressed csg2 Δ mutant cells were indicated to be defective in the trafficking of S nc1 from post‐ G olgi endosomes to the late G olgi. In contrast, the vesicular trafficking pathways via pre‐vacuolar endosomes in the PSS1 ‐ repressed csg2 Δ mutant cells seemed to be normal. These results suggested that specific complex sphingolipids and phosphatidylserine are co‐ordinately involved in specific vesicular trafficking pathway.