Localization of G protein alpha subunits and morphology of receptor neurons in olfactory and vomeronasal epithelia in Reeve's turtle, Geoclemys reevesii

Most vertebrates have two nasal epithelia: the olfactory epithelium (OE) and the vomeronasal epithelium (VNE). The apical surfaces of OE and VNE are covered with cilia and microvilli, respectively. In rodents, signal transduction pathways involve G alpha(olf) and G alpha(i2)/G alpha(o) in OE and VNE, respectively. Reeve's turtles (Geoclemys reevesii) live in a semiaquatic environment. The aim of this study was to investigate the localization of G proteins and the morphological characteristics of OE and VNE in Reeve's turtle. In-situ hybridization analysis revealed that both G alpha(olf) and G alpha(o) are expressed in olfactory receptor neurons (ORNs) and vomeronasal receptor neurons (VRNs). Immunocytochemistry of G alpha(olf/s) and G alpha(o) revealed that these two G proteins were located at the apical surface, cell bodies, and axon bundles in ORNs and VRNs. Electron microscopic analysis revealed that ORNs had both cilia and microvilli on the apical surface of the same neuron, whereas VRNs had only microvilli. Moreover G alpha(olf/s) was located on only the cilia of OE, whereas G(alpha o) was not located on cilia but on microvilli. Both G alpha(olf/s) and G alpha(o) were located on microvilli of VNE. These results imply that, in Reeve's turtle, both G alpha(olf/s) and G alpha(o) function as signal transduction molecules for chemoreception in ORNs and VRNs.