| Development of the Drosophila wing is regulated by the Decapentaplegic (DPP), Wingless (WG) and Hedgehog (HH) signaling pathways. The downstream events that actually coordinate the growth and patterning of the wing, however, are not clear. Scalloped (SD) and Vestigial (VG) are two of the downstream targets of the WG and DPP signaling pathways. SD and VG are expressed in the entire wing, and they are required for the formation of the wing. SD contains a DNA-binding domain whose in vivo activity was not established, and VG is a nuclear protein with no known functional motif. To better understand the process of wing development, molecular and genetic analysis have been carried out to elucidate the mechanism of SD and VG function in normal wing development. Biochemical studies show that SD and VG physically bind to each other. In vivo, the two proteins act cooperatively to promote wing tissue growth. Importantly, the SD-binding domain is absolutely required for VG activity, to induce wing tissue growth and to regulate target genes' expression. These results suggest that SD and VG function as a heterodimeric complex in normal wing development.;The effects of loss of sd activity, overexpression of SD or VG on wing development were then analyzed by making mutant clones or making FLP-out clones in the wing imaginal discs. The lethality of sd mutant clones and SD-overexpressing clones in the wing pouch, and the co-variation between the growth advantage of VG-expressing clones and the endogenous VG levels emphasized the importance of the correct levels of SD and VG in normal wing development. Interestingly, overexpression of VG in the hinge autonomously inhibits and non-autonomously induces WG expression, and VG-expressing clones also exhibit altered cell affinity correlated with the endogenous VG levels. These results imply that the SD/VG dimer plays multiple roles in Drosophila wing development. In addition to promoting wing growth and regulating wing-specific gene expression, SD/VG may also contribute to establishing a gradient of cell affinity across the wing blade, and to segregating the wing blade from the wing hinge. |
