ECTOPIC DECAPENTAPLEGIC IN THE DROSOPHILA MIDGUT ALTERS THE EXPRESSION OF 5 HOMEOTIC GENES, DPP, AND WINGLESS, CAUSING SPECIFIC MORPHOLOGICAL DEFECTS

The patterns of homeotic gene expression in the Drosophila midgut visc eral mesoderm are instrumental in several morphogenetic events, includ ing the formation of the gastric caeca and the positioning of the thre e midgut constrictions. We demonstrate that a potent regulator of home otic gene expression in the visceral mesoderm is the secreted growth f actor-like molecule encoded by the decapentaplegic (dpp) gene. Ectopic dpp in the visceral mesoderm caused changes in the gene expression of Sex combs reduced, Antennapedia, Ultrabithorax (Ubx), and abdominal-A (abd-A) and disrupted the formation of the gastric caeca and the firs t and third midgut constrictions. Ectopic dpp also induced expression of teashirt, wingless (wg) and the endogenous dpp gene in the visceral mesoderm and enhanced labial expression in the adjacent endoderm. The patterns of gene expression and the formation of the second midgut co nstriction in the presence of ectopic dpp are most consistent with a d pp-induced transformation of virtually the entire midgut to cell fates normally seen only in the parasegment (ps)7 and ps8 regions of the mi dgut. We conclude that dpp is a primary signal in maintaining Ubx expr ession in the visceral mesoderm in a pattern different from Ubx expres sion in the embryonic ectoderm and in providing a cell-cell communicat ion mechanism by which Ubx expression influences gene expression acros s germlayers and across the ps7 to ps8 parasegment boundary in the vis ceral mesoderm. (C) 1994 Academic Press, Inc.