Lipid droplets (LDs) are evolutionarily conserved organelles for cellular fat storage. We have previously shown that a loss of DAF-22 function, which attenuates peroxisomal fatty acid beta-oxidation, causes LD expansion and an increase in triglyceride levels. In order to identify genes that are required for LD expansion, we performed a genetic suppressor screen in the
daf-22 mutant background and recovered multiple alleles that fell into at least 5 complementation groups. We report here the molecular cloning of
dgat-2, which encodes a conserved diacylglycerol acyltransferase, the terminal enzyme for triglyceride synthesis. Loss of
dgat-2 function inhibits LD expansion and reduced triglyceride levels of
daf-22 mutant animals while over-expression of DGAT-2 is sufficient to promote LD expansion in wild-type animals. Photo-bleaching demonstrates that DGAT-2 is a LD resident protein. Electron microscopy reveals that DGAT-2 clusters at discreet foci on the LD surface. We engineered a mutant DGAT-2 that was tethered to the ER. This mutant DGAT-2 failed to support LD expansion, indicating that LD localization of DGAT-2 is necessary for its proper function. Our results demonstrate that local synthesis and deposition of triglyceride is critical for LD expansion. We are currently searching for proteins that act in concert with DGAT-2 using genetic and proteomic approaches.