Role of G-Proteins in Odor-Sensing and CO2-Sensing Neurons in Drosophila

A central question in insect chemoreception is whether signaling occurs via G-proteins. Two families of seven-transmembrane-domain chemoreceptors, the odor (Or) and gustatory receptor (Gr) families, have been identified in Drosophila (Clyne et al., 1999, 2000; Vosshall et al., 1999). Ors mediate odor responses, whereas two Grs, Gr21a and Gr63a, mediate CO2 response (Hallem et al., 2004; Jones et al., 2007; Kwon et al., 2007). Using single-sensillum recordings, we systematically investigate the role of G alpha proteins in vivo, initially with RNA interference constructs, competitive peptides, and constitutively active G alpha proteins. The results do not support a role for G alpha proteins in odor sensitivity. In parallel experiments, manipulations of G alpha(q), but not other G alpha proteins, affected CO2 response. Transient, conditional, and ectopic expression analyses consistently supported a role for G alpha(q) in the response of CO2-sensing neurons, but not odor-sensing neurons. Genetic mosaic analysis confirmed that odor responses are normal in the absence of G alpha(q)center dot G gamma 30A is also required for normal CO2 response. The simplest interpretation of these results is that G alpha(q) and G gamma 30A play a role in the response of CO2-sensing neurons, but are not required for Or-mediated odor signaling.