Evolution of divergent functions of the Hox protein Ultrabithorax in insects: comparison in transgenic Drosophila melanogaster

Abstract

The Hox gene, Ultrabithorax (Ubx) mediates haltere development which is the third thoracic segment structure in Drosophila by repressing some of the most important wing patterning genes like wingless, cut and vestigial. Diversity in the T3 segment dorsal morphology is evident in different insect groups. Although Ubx is expressed in the T3 segments in these insects, it has been shown that above mentioned targets of Drosophila Ubx are not differentially expressed between the forewing and hindwings of all insects. Here we chose three insects representing three distinct wing morphology groups viz. Apis mellifera, Bombyx mori and Tribolium custaneum and checked the ability of Ubx protein from these insects to repress the wing patterning genes in Drosophila and thus carry out wing to haltere transformation. We have generated transgenic Drosophila expressing Ubx from Apis, Bombyx and Tribolium. We have shown that Ubx from Apis and Bombyx is able to repress wing patterning genes when over-expressed in the wing imaginal discs of Drosophila and induce wing to haltere transformation. Ability of Ubx from other one insect group to specify haltere development is being investigated. Results suggest that diversity in the T3 segment morphology of these insects is not attributed to the differences in the sequences of Ubx genes and the differential regulation must be brought about downstream to Ubx, perhaps due to evolutionary changes in the enhancer sequences around the region bound by Ubx. To test this hypothesis, we have generated transgenic Drosophila expressing GFP under the control of enhancer of wingless, cut, and vestigial of Apis. These transgenic constructs are currently being tested for their expression patterns under different genetic backgrounds.