When a mouse smells a cat, it instinctively avoids the feline or risks becoming dinner. How? A Northwestern University study involving olfactory receptors, which underlie the sense of smell, provides evidence that a single gene is necessary for the behavior.
A research team led by neurobiologist Thomas Bozza has shown that removing one olfactory receptor from mice can have a profound effect on their behavior. The gene, called TAAR4, encodes a receptor that responds to a chemical that is enriched in the urine of carnivores. While normal mice innately avoid the scent marks of predators, mice lacking the TAAR4 receptor do not.
The study, published April 28 in the journal Nature, reveals something new about our sense of smell: individual genes matter.
Unlike our sense of vision, much less is known about how sensory receptors contribute to the perception of smells. Color vision is generated by the cooperative action of three light-sensitive receptors found in sensory neurons in the eye. People with mutations in even one of these receptors experience color blindness.
"It is easy to understand how each of the three color receptors is important and maintained during evolution," said Bozza, an author of the paper, "but the olfactory system is much more complex."
In contrast to the three color receptors, humans have 380 olfactory receptor genes, while mice have more than 1,000. Common smells like the fragrance of coffee and perfumes typically activate many receptors.
"The general consensus in the field is that removing a single olfactory receptor gene would not have a significant effect on odor perception," said Bozza, an assistant professor of neurobiology in the Weinberg College of Arts and Sciences.
Bozza and his colleagues tested this assumption by genetically removing a specific subset of olfactory receptors called trace amine-associated receptors, or TAARs, in mice. Mice have 15 TAARs. One is
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