Induction of triacylglycerol synthesis in yeast by cell cycle arrest

In this study, we found that cell cycle arrest induced by alpha-factor mating pheromone (G1), hydroxyurea (S) or nocodazole (G2/M) was associated to increased lipid droplet (LD) content. To identify novel cell cycle genes involved in LD homeostasis, we screened a deletion library for strains with altered LD levels. Among the mutants related to mitotic cell cycle, we found 24 hits that displayed a significantly higher LD content. Ontology mapping showed that neither a biological process nor a specific cell cycle phase was enriched among the hits. We decided to further study the role of SWI4 on LD homeostasis as it is involved in G1/S transition, a stage where lipolysis is active. The high LD content of swi4Δ mutant was not due to inhibition of lipolysis, but due to an increase in triacylglycerol (TAG) synthesis. In addition, deletion of the AMP kinase gene SNF1 or inhibition of TORC1 activity, both known regulators of LD homeostasis, further increased the LD content of a swi4Δ mutant. These findings highlight a role of the cell cycle regulator SWI4 in the coordination of lipid metabolism which is independent of the TORC1 and SNF1/AMPK pathways.