Function and regulation of homothorax in the wing imaginal disc of Drosophila

The gene homothorax (hth) is originally expressed uniformly in the wing ima ginal disc but, during development, its activity is restricted to the cells that form the thorax and the hinge, where the wing blade attaches to the t horax, and eliminated in the wing pouch, which forms the wing blade. We sho w that hth repression in the wing pouch is a prerequisite for wing developm ent; forcing hth expression prevents growth of the wing blade. Both the Dpp and the Wg pathways are involved in hth repression. Cells unable to proces s the Dpp (lacking thick veins or Mothers against Dpp activity) or the Wg ( lacking dishevelled function) signal express hth in the wing pouch. We have identified vestigial (vg) as a Wg and Dpp response factor that is involved in hth control. In contrast to its repressing role in the wing pouch, wg u pregulates hth expression in the hinge. We have also identified the gene te ashirt (tsh) as a positive regulator of hth in the hinge, tsh plays a role specifying hinge structures, possibly in co-operation with hth.