DPP INDUCES MESODERMAL GENE-EXPRESSION IN DROSOPHILA

INDUCTIVE interactions between germ layers are an essential feature of the development of many organisms. In several species these interacti ons are mediated by members of the transforming growth factor-beta (TG F beta) family(1,2). In amphibians, different concentrations of activi n can induce different types of mesoderm in the animal cap assay(3-5). In Drosophila, a member of the TGF beta family, decapentaplegic (dpp) (6,7), acts as an inductive signal. Midway through embryogenesis, dpp is expressed in the visceral mesoderm, and enhances the expression of the homeotic gene labial in the underlying midgut endoderm(8,9). Earli er in development, however, dpp expression is limited to the dorsal ec toderm(10). At this stage in development, thickveins, a dpp receptor(1 1-13), is expressed in the mesoderm(12,13), and this suggests that ect odermal dpp might not only be required for development of dorsal ectod erm(14,15), but could also act inductively to mediate pattern formatio n in the underlying mesoderm. Here we show, by expressing dpp ectopica lly in the ectoderm and mesoderm and by examining dpp null mutant embr yos, that dpp regulates expression of mesodermal genes.