Hungry yeast cells use a clever form of recycling to ensure that they can keep consuming stored lipids, Wang et al. show.
Lean times spur yeast cells to enter a quiescent state known as the stationary phase. They break down cached lipids by delivering lipid droplets to the vacuole and resort to autophagy, in which they digest a portion of their own contents. Wang et al. discovered that, to transfer lipid droplets into the vacuole, yeast in the stationary phase rely on a selective form of this process known as microautophagy. In mutant yeast cells that lacked proteins necessary for microautophagy, lipid droplets were locked out of the vacuole.
The vacuole’s membrane contains sterol-rich liquid-ordered domains and more disorganized liquid-disordered domains. Wang et al. determined that lipid droplets can’t cross into vacuoles lacking these domains, and when lipid droplets do enter the vacuole it is specifically through the sterol-rich liquid-ordered domains.
These domains disperse in cells unable to perform autophagy, explaining the loss of lipid droplet transfer under these conditions. Wang et al.’s results further suggest that cells return some of the sterol already inside the vacuole to the liquid-ordered domains. By recycling some of the contents of the lipid droplets already in the vacuole, a yeast cell might ensure an ample supply of liquid-ordered domains that allow the vacuole to absorb and digest additional droplets.
Text by Mitch Leslie