Lipid droplet dynamics during the budding yeast cell cycle influence the timing of cell cycle START

Recent work has revealed that metabolism is dynamic over the budding yeast cell cycle, showing that the NAD(P)H autofluorescence oscillates, and protein and lipid biosynthesis are dynamic. Dynamic storage and liquidation of neutral lipids over the cell cycle could contribute to these metabolic dynamics. However, the dynamics of neutral lipids over the cell cycle are as yet unknown. To elucidate them, we established mNeonGreen-Tgl3 and Pln1-mNeonGreen as protein markers for lipid droplets (LDs) and determined LD dynamics during the cell cycle with single-cell time-lapse microscopy. We found oscillations in the LD number over the cell cycle, with a notable trough around START. Deletion of the genes responsible for either the synthesis of triacylglycerol (TAG) or its mobilisation from LDs lowered LD numbers and abolished the oscillation in LD number. Moreover, in these deletion mutants, we found START to be delayed, suggesting that the mobilisation of TAG from LDs is required for its timely occurrence. The influence of LD dynamics on the timing of START emphasises that research studying cell cycle commitment should consider storage lipid metabolism as a potential contributor to cell cycle START.