Differential expression of G proteins in the mouse olfactory system

Transmembrane signaling events at the dendrites and axons of olfactory rece ptor neurons mediate distinct functions. Whereas odorant recognition and ch emosensory transduction occur at the dendritic membranes of olfactory neuro ns, signal propagation, axon sorting and target innervation are functions o f their axons. The roles of G proteins in transmembrane signaling at the de ndrites have been studied extensively, but axonal G proteins have not been investigated in detail. We used immunohistochemistry to visualize expressio n of or subunits of G(0) and G(i2) in the mouse olfactory system. G(0) is e xpressed ubiquitously on axons of olfactory receptor neurons throughout the olfactory neuroepithelium and in virtually all glomeruli in the main olfac tory bulb. In contrast, expression of G(i2) is restricted to a sub-populati on of olfactory neurons, along the dorsal septum and the dorsal recess of t he nasal cavity, which projects primarily to medial regions of the olfactor y bulb, with the exception of glomeruli adjacent to the pathway of the vome ronasal nerve. In contrast to the overlapping expression patterns of G(0) a nd G(i2) in the main olfactory system, neurons expressing G(0) and those ex pressing G(i2) in the accessory olfactory bulb are more clearly separated, in agreement with previous studies. Vomeronasal axons terminating in glomer uli in the rostral region of the accessory olfactory bulb express G(i2), wh ereas those projecting to the caudal region express G(0). Characterization of the expression patterns of G(i2) and G(0) in the olfactory projection is essential for future studies aimed at relating transmembrane signaling eve nts to signal propagation, axon sorting and target innervation. (C) 1999 El sevier Science B.V. All rights reserved.