Expression Analysis of the 3 G-Protein Subunits, Gα, Gβ, and Gγ, in the Olfactory Receptor Organs of Adult Drosophila melanogaster

In many species, olfactory transduction is triggered by odorant molecules that interact with olfactory receptors coupled to heterotrimeric G-proteins. The role of G-protein-linked transduction in the olfaction of Drosophila is currently under study. Here, we supply a thorough description of the expression in the olfactory receptor organs (antennae and maxillary palps) of all known Drosophila melanogaster genes that encode for G-proteins. Using RT-polymerase chain reaction, we analyzed 6 G alpha (G(s), G(i), G(q), G(o), G(f), and concertina), 3 G beta (G(beta 5), G(beta 13F), and G(beta 76C)), and 2 G gamma genes (G(gamma 1) and G(gamma 30A)). We found that all G alpha protein-encoding genes showed expression in both olfactory organs, but G(f) mRNA was not detected in palps. Moreover, all the G beta and G gamma genes are expressed in antennae and palps, except for G(beta 76C). To gain insight into the hypothesis of different G-protein subunits mediating differential signaling in olfactory receptor neurons (ORNs), we performed immunohistochemical studies to observe the expression of several G alpha and G beta proteins. We found that Gs, Gi, Gq, and G(beta 13F) subunits displayed generalized expression in the antennal tissue, including ORNs support cells and glial cells. Finally, complete coexpression was found between Gi and Gq, which are mediators of the cyclic adenosine monophosphate and IP3 transduction cascades, respectively.