July 7, 2016
Researchers at Hunter College, part of the City University of New York, have created super-sniffer mice that have an increased ability to detect a specific odor, according to a study published July 7 in Cell Reports. The mice, which can be tuned to have different levels of sensitivity to any smell by using mouse or human odor receptors, could be used as land-mine detectors or as the basis for novel disease sensors.
The technology, a transgenic approach to engineering the mouse genome, could also provide researchers with a way to study human odor receptors. "This is one of our five basic senses, yet we have almost no clue how odors are coded by the brain," says lead investigator Paul Feinstein, an associate professor of biological sciences at Hunter. "It's still a black box."
The nature of the odor receptors was discovered in 1991, a Nobel Prize winning feat, but exactly how the olfactory system wires itself still isn't well understood. The noses of mammals contain a collection of sensory neurons, each equipped with a single chemical sensor called a receptor that detects a specific odor. In mice, as in humans, each neuron selects only one receptor. Collectively, neurons choose an even distribution of receptors, so each of the thousand distinct receptors is represented in about 0.1 percent of neurons.
In an effort to understand the mechanism these neurons use to choose a specific receptor, Feinstein tinkered with the mouse genome. He introduced the DNA for an odor receptor gene transgenically, by injection into the nucleus of a fertilized egg cell. He also added an extra string of DNA to the gene sequence to see if it would alter the probability of the gene being chosen. After a few attempts, he found a string that, when copied four or more times, worked.
More copies of this extra string of DNA resulted in a series of super-sniffer mice with increasing numbers of neurons expressing the selected receptor, a well-characterized receptor that detects acetophenone, which has a sweet smell similar to jasmine. The mice still maintain a relatively even distribution of other odor receptors. "We don't know how the neuron performs singular gene choice yet, but we can increase the probability of a given choice occurring," says Feinstein.
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