April 2, 2007

Genetically Altered Mice See a More Colorful World

A row of one blue and two orange panels, with a mouse touching the blue panel A genetically engineered mouse selects the uniquely colored panel and receives a drop of soy milk as a reward.Kris Krogh, University of California, Santa Barbara.

By giving mice the gene that allows people to see red hues, scientists have created rodents that can see a wider range of colors. The study offers clues to the evolution of color vision and suggests that the brains of mammals can quickly adapt to new sensory information.

Like most mammals, mice have only two types of light-detecting "photopigments" in their eyes — one sensitive to the short wavelengths we see as blue and the other to the medium wavelengths we call green. The retinas in the eyes of most primates contain a third type of photopigment sensitive to the longer wavelengths we see as red.

In the new study, described in the March 23, 2007, issue of Science, Dr. Gerald Jacobs of the University of California, Santa Barbara, Dr. Jeremy Nathans of Johns Hopkins University, and their colleagues set out to determine if adding a gene into the mouse genome for a long-wavelength photopigment could enhance the rodents' vision. Their research was supported by the NIH National Eye Institute (NEI) and the Howard Hughes Medical Institute.

The scientists successfully inserted the new gene into mouse embryos so that the resulting mice had all three types of photoreceptor proteins in their retinas. However, it was unclear whether this change by itself would support new color vision or whether the brain would also have to change in order for the mice to perceive the new wavelengths.

To resolve this question, the scientists designed a simple behavioral test. Mice were repeatedly exposed to three illuminated panels, two identical and a third with a different color. The animals were rewarded with a drop of soy milk each time they touched the panel with the unique color. The location, color and brightness of the matching and unique lights changed across trials.

After completing thousands of tests, the researchers found that three of the genetically altered mice achieved an 80% success rate in choosing the different-colored panel. In contrast, normal mice made the correct selection only one-third of the time, the same score that could be achieved by chance.

The researchers say their findings may shed light on the evolution of color vision in primates. More than 40 million years ago, a random change in a photopigment gene created an additional photopigment, sensitive to long wavelengths, in the primate retina. Scientists have long wondered whether the primate brain had to then evolve new connections to derive new color vision. This study suggests that the new gene likely enhanced color perception immediately in these ancient primates, perhaps allowing them to more readily detect ripened fruits and giving them other survival advantages — and ultimately endowing us with a rich, multicolored view of the world.

— by Vicki Contie

Related Links