The heterotrimeric protein G(0) is required for the formation of heart epithelium in Drosophila

The gene encoding the cr subunit of the Drosophila G(o) protein is expresse d early in embryogenesis in the precursor cells of the heart tube, of the v isceral muscles, and of the nervous system. This early expression coincides with the onset of the mesenchymal-epithelial transition to which are subje cted the cardial cells and the precursor cells of the visceral musculature. This gene constitutes an appropriate marker to follow this transition. In addition, a detailed analysis of its expression suggests that the cardiobla sts originate from two subpopulations of cells in each parasegment of the d orsal mesoderm that might depend on the wingless and hedgehog signaling pat hways for both their determination and specification. In the nervous system, the expression of G(o)alpha hortly precedes the begi nning of axonogenesis. Mutants produced in the G(o)alpha gene harbor abnormalities in the three ti ssues in which the gene is expressed. In particular, the heart does not for m properly and interruptions in the heart epithelium are repeatedly observe d, henceforth the brokenheart (bkh) name. Furthermore, in the bkh mutant em bryos, the epithelial polarity of cardial cells was not acquired (or mainta ined) in various places of the cardiac tube. We predict that bkh might be i nvolved in vesicular traffic of membrane proteins that is responsible for t he acquisition of polarity.