fruitlessfunctions downstream ofdoublesexto promote sexual dimorphism of the gonad stem cell niche

SUMMARYBackgrounddoublesex(dsx) andfruitless(fru) are the two downstream transcription factors that actuateDrosophilasex determination. Whiledsxassistsfruto regulate sex-specific behavior, whetherfrucollaborates withdsxin regulating other aspects of sexual dimorphism remains unknown. One important aspect of sexual dimorphism is found in the gonad stem cell (GSC) niches, where male and female GSCs are regulated to create large numbers of sperm and eggs.ResultsHere we report that Fru is expressed male-specifically in the GSC niche and plays important roles in the development and maintenance of these cells. Unlike previously studied regulation of sex-specific Fru expression, which is regulated by alternative splicing by Transformer (Tra), we show that male-specific expression offruis regulated downstream ofdsx, and is independent of Tra. Regulation offrubydsxalso occurs in the nervous system.frugenetically interacts withdsxto support maintenance of the hub throughout development. Ectopic expression offruinhibited female niche formation and partially masculinized the ovary.fruis also required autonomously for cyst stem cell maintenance and cyst cell survival. Finally, we identified a conserved Dsx binding site upstream offrupromoter P4 that regulatesfruexpression in the hub, indicating thatfruis likely a direct target for transcriptional regulation by Dsx.ConclusionsThese findings demonstrate thatfruacts outside the nervous system to influence sexual dimorphism and reveal a new mechanism for regulating sex-specific expression offruthat is regulated at the transcriptional level by Dsx, rather than by alternative splicing by Tra.