Members of a large family of odorant receptors found in olfactory sensory neurons (OSNs) in the main olfactory epithelium detect volatile odorants. Liberles and Buck prepared cDNA and then performed quantitative polymerase chain reaction (qPCR) to search mouse OSNs for G protein-coupled receptors (GPCRs) that had not been implicated previously in taste, odor, or pheromone detection. They identified two members of the trace amine-associated receptor (TAAR) family of GPCRs, which have been hypothesized to act in the brain as receptors for biogenic trace amines, such as tyramine and β-phenylethylamine. Further analysis with qPCR and in situ hybridization indicated that eight of nine mouse taar genes were expressed in olfactory epithelium and that, like odorant receptors, different TAARs are found in different OSNs. TAARs did not appear to be coexpressed with olfactory receptors but were coexpressed with Gαolf, the family of heterotrimeric guanine nucleotide-binding protein (G protein) α subunits through which odorant receptors signal. Individual mouse or human TAARs were coexpressed with an adenosine 3′,5′-monophosphate (cAMP)-dependent reporter gene in HEK293 cells that were cultured with potential ligands. Three mouse TAARs responded to volatile amines present in mouse urine: One detected β-phenylethylamine, which is associated with stress, and two others detected substances present in greater abundance in male than female urine. Thus, the authors propose that the TAARs may represent a family of chemosensory receptors that are functionally distinct from odorant receptors and appear to be associated with the detection of social cues. Ngai discusses implications of the research.
S. D. Liberles, L. B. Buck, A second class of chemosensory receptors in the olfactory epithelium. Nature 442, 645-650 (2006). [PubMed]
J. Ngai, An extra dimension to olfaction. Nature 442, 637-638 (2006). [PubMed]