The Control of Lipid Metabolism by mRNA Splicing in Drosophila. Robert Gingras¹, Bijal Kakrecha³, Nicole Chichearo³, Spencer Ng², Justin DiAngelo¹, Alexis Nagengast². 1) Dept Biol, Hofstra U, NY; 2) Dept Biochem, Widener U, PA; 3) Dept Biol, Widener U, PA.

   The Drosophila fat body responds to different nutrient conditions and controls overall energy metabolism by regulating long-term storage of triglycerides in structures called lipid droplets (LDs), thereby serving a function similar to mammalian liver and adipose tissue. Recent genome-wide RNAi screens in Drosophila cells identified mRNA splicing factors as playing a role in LD formation; their decreased expression results in fewer LDs. Using RNAi under GAL4-UAS control in the fat body of larvae, we have identified several splicing factors that control lipid storage in vivo. Larvae raised on both high and low nutrient food demonstrate a visibly lean phenotype with decreased fat body expression of U1-70K, U2AF-50 or U2AF-38 and prp19 and this lean phenotype corresponds to a decrease in triglyceride levels as measured by quantitative assays. Interestingly, knockdown of the SR protein 9G8 in the larval fat body is male lethal and leads to increased triglycerides on low nutrient food, and decreased triglycerides on high nutrient food. To further probe the role of 9G8 in controlling lipid storage, LD morphology was assessed by staining 9G8 RNAi fat bodies with the lipid stain BODIPY. Fat body-specific knockdown of 9G8 results in more LDs of a medium size compared to control fat bodies that contain a wide range of LD sizes. Previous in vitro studies have implicated 9G8 in the control of doublesex (DSX) splicing by binding to transformer (TRA) and transformer2 (TRA2) to regulate sex determination. To determine whether DSX, TRA or TRA2 play a role in lipid accumulation, LD staining was performed on fat bodies lacking these genes. While knockdown of TRA or TRA2 had little effect on LD morphology, decreasing fat body DSX leads to an increase in LD size. Together, these results suggest a link between mRNA splicing, sex determination and lipid metabolism and may provide insight into the mechanisms underlying tissue-specific splicing and nutrient storage in the fat body.