Transgenic mice see the entire color spectrum

 A mouse that was genetically modified and added a DNA segment that codes for the pigment of the human eye was also able to see all the colors that humans see

Scientists created a vision array of all the colors of the rainbow in the eyes of a mouse, which they added to the poor color mixture that constituted the world of color vision in mice until now, which includes shades of yellow, blue and gray. They did this simply by inserting a segment of DNA that codes for the pigment of the human eye into the mouse genome.
These findings illustrate the flexibility of the mammalian brain and its ability to interpret signals that it does not normally encounter. This also suggests that a single genetic mutation may have caused the red and green hues to be added to the color vision system of our ancestors tens of millions of years ago.
Gerald Jacobs of the University of California at Santa Barbara and his colleagues genetically engineered mice to carry a gene that produces human pigment in their eyes, in addition to the normal mouse pigments. The researchers showed that the introduction of the gene gave the mice the ability to see colors they had not seen before (which mice normally do not have the ability to see).
"The consequences are huge," says David Williams, an eye specialist at the University of Rochester in New York State. "It's amazing to think that the nervous system in the mouse has evolved and adapted to process the new signals and information."
The retina is the tissue that receives the light in the eye and translates the signals into nerve impulses that are sent to the brain. The retina is partly composed of two types of light-receiving cells - cells for night vision that are very sensitive but are not accurate and do not sense color differences, and cells for day vision that require more light to activate but they see accurately and see colors. Color vision in humans is made possible by the fact that there are three different types of day vision cells - some are sensitive to red light, some to green and some to blue. The sensation of all other colors originates from the activation of different combinations of these three types of day vision cells.
Most mammals have day vision cells of only two colors, i.e. only two types of photopigments, therefore they cannot see the red color and a little the green. This means that they see the world in shades of yellow and blue. The two types of photo-pigments in their retina are encoded by two genes, one gene is located on the X chromosome, and the other gene is located on an autosomal chromosome (which is not a sex chromosome). However, many primates, including humans, have a third photopigment, encoded by a second gene located on the X chromosome. The presence of the third photopigment allows for much wider color vision.
When examining the evolution of color, or trichromatic vision, most scientists turn to the New World monkeys, which have an intermediate-genetic set, between a two-pigment system and a three-pigment system. The New World monkeys have only one gene for photopigment on the X chromosome, but there are different versions of this gene, responsible for the production of different pigments (these versions are different alleles of the same gene). As a result, female finches, carrying two X chromosomes, can potentially carry two types of photopigment genes, and thus contain three types of pigments in their eyes.
It is likely that millions of years ago a single mutation resulted in the creation of two versions of the photopigment gene located on the X chromosome. This event may have paved the way for trichromatic vision in both males and females in their primate descendants, says Jeremy Nathans, a scientist who took part in the study the mice
But is an extra photopigment all that is needed to develop trichromatic vision? Or does observing the world, in all its colors, require additional "brain processing power"?
To examine this question, Jacobs and his colleagues created a genetically engineered mouse that effectively mimics the visual system of New World monkeys.
The group of researchers engineered female mice in which one X chromosome carries the normal mouse photopigment gene while the other X chromosome carries the human gene for the pigment. Like female New World monkeys, these transgenic mice produce three types of photopigments, as the team of researchers reported in the journal Science.
Previous studies have shown that these photopigments are able to respond to light. However, can the mice use them to see additional colors - this question remains unanswered. To test this, the researchers conducted a kind of color blindness test for mice.
They presented the mice with three circular panels, each illuminated by light with a different wavelength in the range of 500-600 nm - this is the same range of the visual spectrum that we see as green, yellow and red. In each experiment, one panel was lit differently from the other two; Clicking on the different panel produced soy milk as a reward for the mouse.
Most of the transgenic mice could easily tell the difference when the lights differed by more than 10 nm: three out of five of them pressed the correct panel with their nose or paw in 80% of the 10,000 trials. As for the other two transgenic mice, which did not do so well in the tests, the researchers speculate that the mixture of the three photopigments in their eyes is not so successful.
The meaning of the results is that the mice's brain is without a doubt able to process and decode the new stream of information that comes through the eyes. "This is a beautiful demonstration that relatively complex processing of information can result from a single change in the front of the visual system," says Williams.
The results also suggest that the right type of photopigments may be all that is needed for humans to develop owl-like night vision, or to be able to see in ultraviolet colors. It should be noted that some snakes also see infrared, so they actually see heat (temperature changes). This trait does not exist in mammals - is the inheritance of these traits a single genetic change away? time will tell.
Additional information for this article is from the letter of Prof. Michael Belkin, Eye Research Institute, Sheba Hospital.

For an article on the subject in Nature