Genetic analysis of the bone morphogenetic protein-related gene, gbb, identifies multiple requirements during Drosophila development

We have isolated mutations in the Drosophila melanogaster gene glass bottom boat (gbb), which encodes a TGF-P signaling molecule (formerly referred to as GOA) with highest sequence similarity to members of the bone morphogene tic protein (BMP) subgroup including vertebrate BMPs 5-8. Genetic analysis of both null and hypomorphic gbb alleles indicates that the gene is require d in many developmental processes, including embryonic midgut morphogenesis , patterning of the larval cuticle, fat body morphology, and development an d patterning of the imaginal discs. In the embryonic midgut, we show that g bb is required for the formation of the anterior constriction and for maint enance of the homeotic gene Antennapedia in the visceral mesoderm. In addit ion, we show a requirement for gbb in the anterior and posterior cells of t he underlying endoderm and in the formation and extension of the gastric ca ecae. gbb is required in all the imaginal discs for proper disc growth and for specification of veins in the wing and of macrochaete in the notum. Sig nificantly, some of these tissues have been shown to also require the Droso phila BMP2/4 homolog decapentaplegic (dpp), while others do not. These resu lts indicate that signaling by both gbb and dpp may contribute to the devel opment of some tissues, while in others, gbb may signal independently of dp p.