A Genomic Analysis of Sex Determination. Erin Jimenez¹, Cale Whitworth¹, Emily Clough², Brian Oliver², Mark Van Doren¹. 1) Biology, Johns Hopkins University, Baltimore, MD; 2) NIDDK, National Institutes of Health, Bethesda, MD.

   Sex determination pathways are diverse throughout the animal kingdom, but converge upon conserved genes that encode products that regulate sexual dimorphism. One such downstream factor across many diverged sex determination pathways is the Drosophila doublesex (dsx) gene. The role of dsx is highly conserved in different insects and dsx homologs (dsx, mab-3 related transcription factors, DMRTs) play roles in sexual differentiation in a diverse array of metazoans. In Drosophila, nearly all manifestations of sexual dimorphism between males and females are regulated by dsx, yet there are only three known direct targets of DSX, which cannot account for the differences in regulation by DSX in sexually dimorphic tissues. To gain a comprehensive understanding of DSX targets, we have discovered genes whose transcription is more immediately regulated by DSX by performing transcriptome analysis on samples where the DSX isoform has been acutely changed from DSX-F to DSX-M and vice versa. To control DSX status between sex specific isoforms, we have temperature-controlled alleles of the splicing regulators Transformer-2 and Transformer, which renders expression of either DSX-F or DSX-M temperature dependent. Thus, by switching between DSX protein isoforms DSX-M or DSX-F for an acute period of time, followed by expression profiling, we identified which genes are up- or down-regulated, in response to a change in DSX isoform. By comparing these results to experiments that determine where the DSX protein is bound in the genome, and genetic analysis that identifies new dsx-interacting genes, we have identified a number of target genes. Since the Drosophila gonad represents an excellent model to dissect how DSX acts on a particular time and place to promote development of a sexually dimorphic tissue, we are examining these target genes for roles in gonad sexual development. This research will provide insight into conserved genes that regulate developmentally similar pathways whose outcome generates major differences observed between the sexes.