Dissecting the evolutionary role of the <i>Hox</i> gene <i>proboscipedia</i> in <i>Drosophila</i> mouthpart diversification by full locus replacement.

Abstract

<i>Hox</i> genes determine positional codes along the head-to-tail axis. Here, we replaced the entire <i>Drosophila melanogaster proboscipedia</i> (<i>pb</i>) <i>Hox</i> locus, which controls the development of the proboscis and maxillary palps, with that from <i>Drosophila mimica</i>, a related species with highly modified mouthparts. The <i>D. mimica</i> replacement rescues most aspects of adult proboscis morphology; however, the shape and orientation of maxillary palps were modified, resembling <i>D. mimica</i> and closely related species. Expressing the <i>D. mimica</i> Pb protein in the <i>D. melanogaster</i> pattern fully rescued <i>D. melanogaster</i> morphology. However, the expression pattern directed by <i>D. mimica pb</i> cis-regulatory sequences differed from that of <i>D. melanogaster pb</i> in cells that produce altered maxillary structures, indicating that <i>pb</i> regulatory sequences can evolve in related species to alter morphology.