The genetic regulation of sex-specific motorneurons by the doublesex gene in Drosophila melanogaster and the genetic characterization of an interaction with the sex determination hierarchy Public Deposited

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  • The remodeling of the central nervous system (CNS) during metamorphosis in Drosophila melanogaster is a prime model system in which to study the genetic control of the sexual dimorphisms in the abdominal ganglion of the CNS. I have been using a P[tau-lacZ] enhancer trap line, 4.078, to label a segmentally repeated subset of abdominal motorneurons in order to assess the function of the sex determination hierarchy in controlling sex-specific development of the adult nervous system. In both the male and female larva there are 8 sets of these labeled abdominal motorneurons but only six sets in males and five sets in females survive in the adult. When this P[tau-lacZ] reporter construct is placed into a doublesex (dsx) mutant background, all 8 sets of these labeled abdominal motorneurons survive in both male and female adults. These results strongly suggest that dsx plays a role in the sex-specific survival of larval neurons that have functions in the adult. During the construction of mutant strains containing the sex determining genes transformer (tra) and transformer-2 (tra2), a genetic interactor was discovered in the P[tau-lacZ] 4.078 line. Female flies heterozygous for either tra or tra-2 alleles and the P[tau-lacZ] 4.078 developed with masculinized external and internal sex-specific structures. The external sex-specific structures, such as the genitalia, and ventral muscles are dependent on dsx gene function and a dorsal sex-specific muscle is dependent on fruitless (fru) gene function. From standard genetic crosses, I have characterized and demonstrated that the genetic interaction is linked to the P-element insertion site, which maps to the 85-87 region on the right arm of the third chromosome. By genetic analysis, this new genetic interactor appears to interfere with the tra and tra2 regulated female specific functions of both dsx and fru, potentially by reducing the female-specific splicing of the primary transcripts of the genes dsx and fru. To test the possibility that this newly described genetic interactor was allelic to a known gene, B52, that maps to the same region of the chromosome and alters dsx splicing, complementation tests were conducted which showed that the P[tau-lacZ] is not allelic B52. Additional phenotypes were observed in the crosses that first detected the interaction, suggesting that this newly described locus may affect other gene functions as well. Among the phenotypes observed were XX intersexes, male-female gynandromorphs (XX//XO mosaics), and non-disjunction events evident as XO males and XXY females. This new locus may represent a new member of the family of genes that influence regulated splicing events.
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