A positive role in differentiation for the male doublesex protein of Drosophila.

The doublesex (dsx) locus encodes male-specific and female-specific polypeptides that are essential for the proper differentiation of sexually dimorphic somatic features of Drosophila melanogaster. Ectopic expression of the male-specific dsx polypeptide was obtained by P-element-mediated transformation of flies with a construct bearing a fusion between the hsp70 heat shock promoter and dsx male-specific cDNA sequences. Heat shock-induced expression of the male cDNA in either sex resulted in three novel phenotypes: transformation of bristles on all legs toward a sex comb-like morphology, pigmentation of dorsal spinules and ventral setae in third-instar larvae, and lethality. These results were not predicted by previous models of dsx function, and provide evidence that the role of the male dsx protein includes activation of some aspects of male differentiation as well as repression of female differentiation.