It's Not Easy Seeing Green: Improving Mice Vision with a Single Gene

Scientists have discovered that mice can see new colors with the insertion of a single human gene into a mouse chromosome. The study, published in the March 2007 issue of the journal Science, demonstrates that sight can be profoundly altered with simple genetic changes.

Unlike humans, mice are naturally only able to see certain wavelengths of light, similar to people that are red-green color blind. By introducing a single human gene into a mouse chromosome, researchers at the Johns Hopkins School of Medicine have demonstrated that the resulting transgenic mouse is able to distinguish among a broader spectrum of light waves. Humans have trichromatic vision due to the presence of three different photoreceptor cone cells in the retina and most other mammals (including mice) have dichromatic vision. Each type of photoreceptor cell corresponds to the wavelength that it is most sensitive to (short, medium, or long), and mice normally have only short wavelength (S) and medium wavelength (M) cone cells.

After the Johns Hopkins scientists created mice that are also sensitive to long wavelength (L) light, they tested the mice with a series of cleverly designed color vision tests. One of the tests involved two colors that were displayed on three test panels, one of which would not be detected as different by normal mice. If the mouse picked the differing color, then it was rewarded with a drop of soy milk. The scientists found that the transgenic mice picked the correct color 80% of the time, while control mice only picked it 33% of the time, demonstrating that the transgenic mice could detect a broader spectrum of light. Through this research, the scientists proposed a model for how the evolution of color vision might have evolved in primates.

"What we are looking at in these mice is the same evolutionary event that happened in one of the distant ancestors of all primates and that led ultimately to the trichromatic color vision that we now enjoy," said Jeremy Nathans, a Howard Hughes Investigator at Johns Hopkins. This result brings new light to the plasticity of the nervous system, and may be key in understanding how other senses (such as smell and taste) may be controlled by genetic factors.

- By Frances Mao.

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