Mad acts downstream of Dpp receptors, revealing a differential requirement for dpp signaling in initiation and propagation of morphogenesis in the Drosophila eye.

Decapentaplegic (Dpp), a member of the TGF-beta family of cytokines, has been implicated in many patterning processes in Drosophila, including the initial steps of pattern formation in the developing eye. We show that the Mothers against dpp (Mad) gene is required for dpp signaling during eye development. Clonal analysis demonstrates a cell-autonomous function for Mad and genetic interactions indicate that Mad is an essential component of the signal transduction pathway downstream of the Dpp receptors in responding cells. Mad-mediated dpp signaling is absolutely required for the initiation of the morphogenetic furrow in the eye, but has only a minor role in its subsequent propagation across the eye disc. We also present evidence for the repression of wingless transcription by dpp signaling.