Role of G(o/i) subgroup of G proteins in olfactory signaling of Drosophila melanogaster

Intracellular signaling in insect olfactory receptor neurons remains unclear, with both metabotropic and ionotropic components being discussed. Here, we investigated the role of heterotrimeric G(o) and G(i) proteins using a combined behavioral, in vivo and in vitro approach. Specifically, we show that inhibiting G(o) in sensory neurons by pertussis toxin leads to behavioral deficits. We heterologously expressed the olfactory receptor dOr22a in human embryonic kidney cells (HEK293T). Stimulation with an odor led to calcium influx, which was amplified via calcium release from intracellular stores. Subsequent experiments indicated that the signaling was mediated by the Gβγ subunits of the heterotrimeric G(o/i) proteins. Finally, using in vivo calcium imaging, we show that G(o) and G(i) contribute to odor responses both for the fast (phasic) as for the slow (tonic) response component. We propose a transduction cascade model involving several parallel processes, in which the metabotropic component is activated by G(o) and G(i), and uses Gβγ.