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Many cells store neutral lipids, as triacylglycerol and sterol esters, in droplets. PAT-domain proteins form a conserved family of proteins that are localized at the surface of neutral lipid droplets. Two mammalian members of this family, Perilipin and adipose differentiation-related protein, are involved in lipid storage and regulate lipolysis. Here, we describe the Drosophila PAT-family member Lsd2. We showed that Lsd2 is predominantly expressed in tissues engaged in high levels of lipid metabolism, the fat body and the germ line of females. Ultrastructural analysis in the germ line showed that Lsd2 localizes to the surface of lipid droplets. We have generated an Lsd2 mutant and described its phenotype. Mutant adults have a reduced level of neutral lipid content compared to wild type, showing that Lsd2 is required for normal lipid storage. In addition, ovaries from Lsd2 mutant females exhibit an abnormal pattern of accumulation of neutral lipids from mid-oogenesis, which results in reduced deposition of lipids in the egg. Consistent with its expression in the female germ line, we showed that Lsd2 is a maternal effect gene that is required for normal embryogenesis. This work demonstrates that Lsd2 has an evolutionarily conserved function in lipid metabolism and establishes Drosophila melanogaster as a new in vivo model for studies on the PAT-family of proteins.

Translational regulation of localized transcripts is a powerful mechanism to control the precise timing and localization of protein expression within a cell. In the Drosophila germline, oskar transcript must be translationally repressed until its localization at the posterior pole of the oocyte, as ectopic production of Oskar causes severe patterning defects. Translational repression of oskar mRNA is mediated by the RNA-binding protein Bruno, which binds to specific motifs in the oskar 3'UTR. Here we show that Bruno over-expression causes defects in antero-posterior and dorso-ventral patterning, consistent with a role of Bruno in both oskar and gurken mRNA regulation. We also show that Bruno and gurken interact genetically. Finally, we show that Bruno binds specifically to the gurken 3'UTR and that the dorso-ventral defects caused by Bruno over-expression are due to a reduction of Gurken levels in the oocyte. We conclude that Bruno plays similar roles in translational regulation of gurken and oskar.