A novel brain receptor is expressed in a distinct population of olfactory sensory neurons

Three novel G-protein-coupled receptor genes related to the previously desc ribed RA1c gene have been isolated from the mouse genome. Expression of the se genes has been detected in distinct areas of the brain and also in the o lfactory epithelium of the nose. Developmental studies revealed a different ial onset of expression: in the brain at embryonic stage 17, in the olfacto ry system at stage E12. In order to determine which cell type in the olfact ory epithelium expresses this unique receptor type, a transgenic approach w as employed which allowed a coexpression of histological markers together w ith the receptor and thus visualization of the appropriate cell population. It was found that the receptor-expressing cells were located very close to the basal membrane of the epithelium; however, the cells extended a dendri tic process to the epithelial surface and their axons projected into the ma in olfactory bulb where they converged onto two or three glomeruli in the d orsal and posterior region of the bulb. Thus, these data provide evidence t hat this unique type of receptor is expressed in mature olfactory neurons a nd suggests that it may be involved in the detection of special odour molec ules.