Molecular bases of odor discrimination: Reconstitution of olfactory receptors that recognize overlapping sets of odorants.
The vertebrate olfactory system discriminates a wide variety of odorants by relaying coded information from olfactory sensory neurons in the olfactory epithelium to olfactory cortical areas of the brain. Recent studies have shown that the first step in odor discrimination is mediated by approximately 1000 distinct olfactory receptors, which comprise the largest family of G-protein-coupled receptors. In the present study, we used Ca(2+) imaging and single-cell reverse transcription-PCR techniques to identify mouse olfactory neurons responding to an odorant and subsequently to clone a receptor gene from the responsive cell. The functionally cloned receptors were expressed in heterologous systems, demonstrating that structurally related olfactory receptors recognized overlapping sets of odorants with distinct affinities and specificities. Our results provide direct evidence for the existence of a receptor code in which the identities of different odorants are specified by distinct combinations of odorant receptors that possess unique molecular receptive ranges. We further demonstrate that the receptor code for an odorant changes with odorant concentration. Finally, we show that odorant receptors in human embryonic kidney 293 cells couple to stimulatory G-proteins such as Galphaolf, resulting in odorant-dependent increases in cAMP. Odor discrimination is thus determined by differences in the receptive ranges of the odorant receptors that together encode specific odorant molecules.
Kajiya
K
K
Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Tokyo 113, Japan.
Inaki
K
K
Tanaka
M
M
Haga
T
T
Kataoka
H
H
Touhara
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003001:Cloning, Molecular; D000242:Cyclic AMP / Q000378:metabolism; D005456:Fluorescent Dyes; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009812:Odorants; D018034:Olfactory Receptor Neurons / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D018035:Receptors, Odorant / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000502:physiology; D012903:Smell / Q000502:physiology*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity / Q000502:physiology; D014162:Transfection
D005456:Fluorescent Dyes; D018035:Receptors, Odorant; D000242:Cyclic AMP; D019205:GTP-Binding Protein alpha Subunits, Gs; D002118:Calcium