Abstract
Hox transcription factors are deeply conserved proteins that guide development through regulation of diverse target genes. Furthermore, alteration in Hox target cis-regulation has been proposed as a major mechanism of animal morphological evolution. Crucial to understanding how homeotic genes sculpt the developing body and contribute to the evolution of form is identification and characterization of regulatory targets. Because target specificity is achieved through physical or genetic interactions with cofactors or co-regulators, characterizing interactions between homeotic genes and regulatory partners is also critical. In Drosophila melanogaster, sexually dimorphic abdominal morphology results from sex-specific gene regulation mediated by the Hox protein Abdominal-B (Abd-B) and products of the sex-determination gene doublesex (dsx). Together these transcription factors regulate numerous sex-specific characters, including pigmentation, cuticle morphology, and abdominal segment number.We show Dsx expression in the developing D. melanogaster pupal abdomen is spatiotemporally dynamic, correlating with segments that undergo sexually dimorphic morphogenesis. Furthermore, our genetic analyses show Dsx expression is Abd-B dependent.Doublesex and Abd-B are not only requisite co-regulators of sexually dimorphic abdominal morphology. We propose that dsx is itself a transcriptional target of Abd-B. These data present a testable hypothesis about the evolution of sexually dimorphic segment number in Diptera.
