An important role for triglyceride in regulating spermatogenesis

Drosophila is a powerful model to study how lipids affect sperm development1–3. Studies in flies showed that phosphatidylinositol and its phosphorylated derivatives influence spermatogenesis4–14, and uncovered roles for membrane lipids and fatty acids in this process15–19. Less is known about how neutral lipids, another major lipid group, affect sperm development. Neutral lipids include triglycerides and cholesterol esters, and reside within specialized organelles called lipid droplets (LD)20. Emerging evidence shows testis LD are present in normal and stressful contexts21–26. Genes associated with neutral lipid metabolism and LD also show testis expression27–29, and dysregulation of these genes causes subfertility30–32. Yet, many questions remain about the spatial, temporal, and cell type-specific requirements for neutral lipids and LD during spermatogenesis. Here, we show that LD are present in early-stage somatic and germline cells within the Drosophila testis. We identified a role for triglyceride lipase brummer (bmm) in regulating testis LD, and show that whole-body and cell-autonomous loss of bmm leads to defects in sperm development. Because lipidomic analysis of bmm mutants revealed excess triglyceride accumulation, and spermatogenic defects in bmm mutants were rescued by genetically blocking triglyceride synthesis, our data suggest that bmm-mediated regulation of triglyceride influences sperm development. This identifies triglyceride as an important neutral lipid that contributes to Drosophila sperm development, and reveals a key role for bmm in regulating testis triglyceride levels and spermatogenesis.