Regulation of wingless by Abd-B and Doublesex and the evolution of male abdominal segment reduction in Drosophila. Wei Wang, John Yoder. Department of Biological Sciences, The University of Alabama, Tuscaloosa, AL.

   Male-specific reduction in adult abdominal segment number is a trait shared by all Cyclorrhaphan diptera. As such this is as an attractive model for investigating developmental and evolutionary mechanisms underlying morphological innovation. Drosophilid females possess 7 abdominal segments, while the terminal segment in males (A7) is significantly reduced during pupation. A major mechanism promoting male A7 reduction is sex- and segment specific repression of the morphogen encoding wingless (wg) gene by the Hox protein Abdominal-B (Abd-B) and the sex-determination transcription factor Doublesex (Dsx). To investigate whether Abd-B and Dsx directly regulate wg expression we have performed a systematic molecular screen to identify cis-regulatory elements (CREs) governing wg expression in the Drosophila melanogaster pupal abdomen.Two distinct abdominal CREs were identified. One CRE promotes abdominal-specific expression (wg1) while the second CRE(wg2) drives reporter expression in additional imaginal tissue including the genital disc. Both CREs contain multiple putative Abd-B binding sites as well as Dsx consensus sites.While these potential regulatory sites are largely conserved in wg2, Dsx binding sites in wg1 have been lost within several lineages of the Drosophila genus group. Interestingly, these losses correlate with modified male A7 morphology suggesting that evolutionary alteration to wg regulation promoted partial restoration of male A7 in some species.We will present comparative functional analyses of these CREs investigating 1) their direct regulation by Abd-B and Dsx and 2) their relative contributions to wg expression in these diverse lineages. This study will provide a critical genetic context in which to explore the role of wg regulation in the evolution of segment reduction as well as provide insight into constraints acting on, as well as the degree of evolutionary flexibility within, a deeply fixed trait.