Sexual dimorphism and developmental expression of signal-transduction machinery in the vomeronasal organ

We have explored the use of a new model to study the transduction of chemosignals in the vomeronasal organ (VNO), for which the functional pathway for chemical communication is incompletely understood. Because putative vomeronasal receptors in mammalian and other vertebrate models belong to the superfamily of G-protein-coupled receptors, the objective of the present study was to define which G-protein subunits were present in the VNO of Sternotherus odoratus (stinkpot or musk turtle) in order to provide directionality for future functional studies of the downstream signaling cascades. The turtle vomeronasal epithelium (VNE) was found to contain the G-proteins G_β and G_αi1-3 at the microvillar layer, the presumed site of signal tranduction in these neurons, as evidenced by immunocytochemical techniques. G_αo labeled the axon bundles in the VNE and the somata of the vomeronasal sensory neurons but not the microvillar layer. Densitometric analysis of Western blots indicated that the VNO from females contained greater concentrations of G_αi1-3 compared with males. Sexually immature (juvenile) turtles showed intense immunolabeling for all three subunits (G_β, G_αi1-3, and G_αo) in the axon bundles and an absence of labeling in the microvillar layer. Another putative signaling component found in the microvilli of mammalian VNO, transient receptor potential channel, was also immunoreactive in S. odoratus in a gender-specific manner, as quantified by Western blot analysis. These data demonstrate the utility of Sternotherus for discerning the functional signal transduction machinery in the VNO and may suggest that gender and developmental differences in effector proteins or cellular signaling components may be used to activate sex-specific behaviors.