Fission yeast ceramide ts mutants cwh43 exhibit defects in G0 quiescence, nutrient metabolism, and lipid homeostasis

Abstract

Cellular nutrient states control whether cells proliferate, or whether they enter or exit quiescence. Here, we report characterizations of fission yeast temperature-sensitive (ts) mutants of the evolutionarily conserved transmembrane protein, Cwh43, and explore its relevance to utilization of glucose, nitrogen-source, and lipids. GFP-tagged Cwh43 localizes at ER associated with the nuclear envelope and the plasma membrane, as in budding yeast. We found that cwh43 mutants failed to divide in low glucose and lost viability during quiescence under nitrogen starvation. In cwh43 mutant, comprehensive metabolome analysis demonstrated dramatic changes in marker metabolites that altered under low glucose and/or nitrogen starvation, although cwh43 apparently consumed glucose in the culture media. Furthermore, we found that cwh43 mutant had elevated levels of triacylglycerols (TGs) and coenzyme A, and that it accumulated lipid droplets. Notably, TG biosynthesis was required to maintain cell division in cwh43 mutant. Thus, Cwh43 affects utilization of glucose and nitrogen-sources, as well as storage lipid metabolism. These results may fit to a notion developed in budding yeast that Cwh43 conjugates ceramide to GPI (glycosylphosphatidylinositol)-anchored proteins and maintains integrity of membrane organization.