Size and shape control by Hox genes

We study how the Hox genes determine the different size of particular organs. We investigate, for instance, how the Hox gene Ultrabithorax controls the different size of the adult metanotum (dorsal part of the third thoracic segment, T3), and that is greatly reduced as compared to the mesonotum (dorsal part of the second thoracic segment, T2). In Ultrabithorax mutants the T3 is transformed into T2, so this gene reduces the size of the T3. In a similar analysis, we would like to know the mechanisms whereby Hox genes regulate different proliferation in the histoblasts, cells that give rise to the abdomen, or in the imaginal discs, since the former divide only during pupal stages and the latter mainly during the larval period. Finally, we want to analyze the reason for the size difference in the segments that form the genitalia, which requires the coordination between the Hox gene Abdominal-B and the sex determination genes. The different proliferation of the genital disc segments is established by the Hox Abdominal-B gene together with sex determination genes and is mediated, among others, by the Decapentaplegic and Hippo signaling pathways (Fig. 1).

We also study how Hox genes determine form. Thus, we analyze the mechanisms whereby Ultrabithorax determines the globular form of the halteres (dorsal appendages in the thorax) as opposed to the flat appearance of wings. We think this difference may be implemented by changes in the extracellular matrix in early pupal stages regulated by Ultrabithorax.