Insects display an astonishing array of diversity in flight appendage morphologies. One of the most striking modifications is the transformation of hindwings into highly reduced balancing structures called halteres. Work in Drosophila established that the specification of halteres is under the control of a single Hox gene, Ultrabithorax (Ubx). In contrast, the formation of forewings is Hox-independent, leading to the general assumption that all wings in insects are a Hox-free state.
During my PhD, I reconsidered the role of Hox genes for flight appendage specification in Drosophila. My work showed that a low expression level of the Hox gene Antennapedia (Antp) is required for the correct formation of the distal part of the adult wing. Interestingly, increasing this expression level is sufficient to induce wing-to-haltere transformation phenotypes, reproducing thus Ubx-like function. Expressing Antp in place of Ubx is also sufficient to rescue the four-wings Ubx mutant phenotype. By genetically affecting the expression level of endogenous Ubx, I could further demonstrate that the specification of halteres is tightly linked to a high dose of the Hox protein. Finally, by investigating Hox doses in different insect species, I could observe that four wings insect species have subtle variations in the Hox dose between forwing and hindwing primordia. My PhD work establishes a novel paradigm whereby variation of the Hox expression level is sufficient to modify the wing size and shape, ultimately leading to a complete new balancing structure as observed in dipterans during insect evolution.
Gratuit
Disciplines