The missense of smell: functional variability in the human odorant receptor repertoire.


Humans have ~400 intact odorant receptors, but each individual has a unique set of genetic variations that lead to variation in olfactory perception. We used a heterologous assay to determine how often genetic polymorphisms in odorant receptors alter receptor function. We identified agonists for 18 odorant receptors and found that 63% of the odorant receptors we examined had polymorphisms that altered in vitro function. On average, two individuals have functional differences at over 30% of their odorant receptor alleles. To show that these in vitro results are relevant to olfactory perception, we verified that variations in OR10G4 genotype explain over 15% of the observed variation in perceived intensity and over 10% of the observed variation in perceived valence for the high-affinity in vitro agonist guaiacol but do not explain phenotype variation for the lower-affinity agonists vanillin and ethyl vanillin.





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Publication Info

Mainland, Joel D, Andreas Keller, Yun R Li, Ting Zhou, Casey Trimmer, Lindsey L Snyder, Andrew H Moberly, Kaylin A Adipietro, et al. (2014). The missense of smell: functional variability in the human odorant receptor repertoire. Nat Neurosci, 17(1). pp. 114–120. 10.1038/nn.3598 Retrieved from

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Hiroaki Matsunami

Professor of Molecular Genetics and Microbiology

We are interested in the molecular mechanisms underlying chemosensation (taste and smell) in mammals. The receptors that detect odorants, pheromones, and many tastants including bitter and sweet chemicals are G-protein coupled receptors (GPCRs), which typically have seven transmembrane domains. There are many important questions that are still unanswered in chemosensory neurobiology. How do tens of thousands of different chemicals (tastants, odorants, or pheromones) interact with more than one thousand chemosensory receptors (about 1000 odorant receptors, 40 taste receptors and 200 vomeronasal receptors in the case of mice or rats)? How is the information coded in sensory cells and in the brain? How does the brain direct appropriate behavioral responses? What are the mechanisms underlying development and regeneration of sensory cells and specific synapse connections? We address these questions using molecular biology, genome information and genetics.

The detection of tastants is mediated by taste receptor cells that are clustered in taste buds in the mouth. Interestingly, some people can taste certain chemicals, such as 6-n-propylthiouracil (a bitter compound) while others can't. Likewise, some strains of mice can taste certain bitter or sweet tastants while others can't. Based on these variations, the bitter and sweet taste loci have been mapped on human or mouse chromosomes. By using the increasingly powerful genome informatics tools, we as well as other groups, have identified families of GPCRs that may detect bitter and sweet compounds. We seek to understand how specific changes in nucleotide sequences cause these differences in taste sensitivity. Another goal is to understand how the gustatory system is organized.

In olfaction, the detection of volatile odorants is mediated by olfactory sensory neurons in the olfactory epithelium of the nose. Odorants are detected by about 1000 different types of odorant receptors that are encoded by a multigene family. Each olfactory sensory neuron expresses only one receptor type out of 1000 receptors. Axons of neurons expressing the same receptor all converge in a few glomeruli in the olfactory bulb of the brain. We wish to understand the mechanisms underlying this convergence.

Finally, we are interested in the pheromone sensing system. Pheromones are chemicals that are released from animals and induce innate behavior, such as mating or aggression, or hormonal changes in members of the same species.
The detection of pheromones is mediated primarily by a second olfactory sense organ, called the vomeronasal organ (VNO). We, as well as other groups, have found families of candidate pheromone receptors by comparing gene expression between single VNO neurons. Pheromone molecules may induce their effects by activating some of these receptors, which ultimately affect particular regions of the brain. We seek to understand how these pheromonal effects are mediated.

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