GENOMIC REGIONS REQUIRED FOR MORPHOGENESIS OF THE DROSOPHILA EMBRYONIC MIDGUT

The Drosophila midgut is an excellent system for studying the cell mig ration, cell-cell communication, and morphogenetic events that occur i n organ formation. Genes representative of regulatory gene families co mmon to all animals, including homeotic, TGF beta, and Wnt genes, play roles in midgut development. To find additional regulators of midgut morphogenesis, we screened a set of genomic deficiencies for midgut ph enotypes. Fifteen genomic intervals necessary for proper midgut morpho genesis were identified; three contain genes already known to act in t he midgut. Three other genomic regions are required for formation of t he endoderm or visceral mesoderm components of the midgut. Nine region s are required for proper formation of the midgut constrictions. The E 75 ecdysone-induced gene, which encodes a nuclear receptor superfamily member, is the relevant gene in one region and is essential for prope r formation of midgut constrictions. E75 acts downstream of the previo usly known constriction regulators or in parallel. Temporal hormonal c ontrol may therefore work in conjunction with spatial regulation by th e homeotic genes in midgut development. Another genomic region is requ ired to activate transcription of the homeotic genes Anti, and Scr spe cifically in visceral mesoderm. The genomic regions identified by this screen provide a map to novel midgut development regulators.