Studies on the transcriptional regulation underlying Drosophila melanogaster sex-specific behaviors

In Drosophila melanogaster, nearly all sexual dimorphism is controlled by the sex-determination hierarchy. At the top of this genetic regulatory cascade are genes that encode splicing factors that are produced in a sex-specific manner in response to the dose of a set of X chromosome genes. The cascade culminates in the production of sex-specific transcription factors, encoded by two genes whose transcripts are sex-specifically spliced--- doublesex (dsx) and fruitless ( fru). These sex-specific transcription factors are responsible for directing most aspects of sexual dimorphism, including sex-specific behaviors. Two of the most interesting and easily identifiable sex-specific behaviors are the male courtship and female post-mating behaviors. Although the male and female nervous systems are nearly indistinguishable on a gross anatomical scale, higher resolution analysis has identified sexual dimorphism in neuronal number and arborization patterns in subsets of neurons. These differences are thought to establish the ability to perform sex-specific behaviors. Although, FruM is necessary for specifying dimorphism in the neural circuit and the potential for courtship, how FruM facilitates these differences remains unclear. To address this, we sought to identify genes regulated downstream of FruM in males, during metamorphosis, when the nervous system is undergoing large developmental changes, particularly those necessary for adult sex-specific behaviors. This led to the identification of a set of genes, which are also known to be regulated downstream of the steroid hormone, ecdysone. Functional characterization of the receptor for ecdysone (EcR), within the male fru-expressing neuronal circuitry, revealed that one EcR isoform (EcR-A) is necessary for wildtype discrimination of males and females as targets for courtship, and for the establishment of male-specific arborization patterns in the antennal lobe. In addition to the regulatory roles FruM plays during metamorphosis, we also extended our analysis to adult stages, to identify FruM regulated genes within head and brain tissues. We identify multiple FruM-regulated genes in adult heads and brains, and showed that two of these genes are necessary for courtship behavior. Furthermore, we find that FruM isoforms, which differ in their predicted DNA binding domain, may regulate a common set of genes, though some isoform-specific transcriptional roles are apparent. Additionally, we find a number of genes regulated by both DsxM and FruM, including those with known expression in fat body tissues. Finally, we determined the transcriptional changes that accompany the female post-mating behavioral response. We find that female post-mating behavior is accompanied by large gene expression changes, with genes that encode products involved in metabolic processes showing large differences at many post-mating stages. Additionally, we find that modification of neuronal physiology likely underlies the post-mating response, as multiple genes encoding ion channels were found with transcription changes. The data presented here examines sex hierarchy transcriptional regulation and its implications for establishing the potential for sex-specific behaviors.