THE TRANSDUCTION SIGNALING PROTEIN-GO DURING EMBRYONIC-DEVELOPMENT OF DROSOPHILA-MELANOGASTER

G proteins are heterotrimeric proteins that play a key role in signalling transduction conveying signals from cell surface receptors to intracellular effector proteins. In particulate preparations from Drosophila melanogaster embryos, only one substrate of 39,000-40,000 molecular weight could be ADP-ribosylated with pertussis toxin. This substrate reacted in immunoblotting and immunoprecipitation experiments with a polyclonal antibody directed against the carboxy-terminal sequence of the alpha-subunit of the mammalian G(o) protein. The Drosophila G(o-alpha) protein was present at all stages of embryonic development; however, its expression markedly increased after 10 h of embryogenesis, a period of time during which there is an active development of axonal tracts. Immunolocalization on whole mount embryos has indicated that this protein is principally localized in the CNS and is mainly restricted to the neuropil without any labelling of the cell bodies. In contrast, all the axon tracts of the CNS appeared to be highly labelled. The distribution of the G(o-alpha) protein was also examined in several neurogenic mutants. The G(o-alpha) expression was not altered in any of them but the pattern of labelling was disorganized as was the neuronal network. These results suggest a possible role for the G(o) protein during axonogenesis.