"Seeing the World in a New Light"

[Xar]

Aside from primates, most mammals are largely colorblind. Now researchers have found that transgenic mice can acquire the ability to detect new color differences if given a gene for making an additional light-sensing eye protein. The findings have implications for understanding how color vision evolved.

Primates can distinguish the colors of the rainbow better than other mammals because their eyes contain three photopigment proteins. Each photopigment is sensitive to light of a particular wavelength, and the primate visual system detects colors by comparing the relative activity of cells in the retina that bear each of the three photopigments. Most other mammals, however, only make two photopigments, limiting their color discrimination. Scientists have suggested that trichromatic color vision arose in primates when one of the two photopigment genes they already had mutated to produce a third photopigment.

A sudden mutation like this could have given primates an instant advantage when it came to finding food--but only if their visual system were able to make sense of the new information. Certain differences in retina anatomy between primates and other mammals led many researchers to suspect that only primates had the right kind of wiring to make use of a sudden addition of a third photopigment.

But perhaps not. In the new experiment, vision scientist Gerald Jacobs at the University of California, Santa Barbara, teamed up with geneticist Jeremy Nathans at Johns Hopkins Medical School in Baltimore, Maryland, and other colleagues to add a human photopigment gene to mice. Electrical recordings from the retinas of the engineered mice indicated that the added photopigment had enabled their color-sensing cone cells to respond to long wavelength red light, which normal mice can't see. Next the team gave the mice a battery of behavioral tests that required them to poke their nose at panels in their enclosure to indicate which of three panels was a different color than the other two. Right answers earned a tiny drop of soy milk ("It's kind of hippie-ish, but they really enjoy it," Jacobs says.) The engineered mice passed with flying colors, so to speak, making distinctions that regular mice cannot, the researchers report in tomorrow's Science.

The work supports the idea that a single gene mutation could have produced trichromatic color vision and immediate changes in behavior, says Daniel Osorio, a vision scientist at Sussex University, U.K. At the same time, Osorio says, it creates a mystery about why such color vision didn't evolve in other mammals, too.

[Avatar]

Just read this article today myself. Fascinating that immediate behaviour changes occur.

--A

[Xar]

Just read this article today myself. Fascinating that immediate behaviour changes occur.

--A

Well, you have to realize these are genetically engineered mice - that is, they were already born with this ability, they didn't suddenly gain it. It would be interesting to see how animals who are given this photopigment after adulthood - say, through virus-mediated gene transfer, or other such methods - would cope with the sudden new vistas.

[wayfriend]

Is three the key? Or are we colorblind compared to anyone that had four (or five) different photopigments?

[Xar]

Is three the key? Or are we colorblind compared to anyone that had four (or five) different photopigments?

Well, we are colorblind about, say, UV light or infrared light... while some creatures can see in those wavelengths. So technically, if this discovery held true, it would mean that it could be possible to just insert the gene for one such photopigment in a human and allow him/her to see in conditions of low light, or into the UV spectrum...

[wayfriend]

So the "colorblindness" of the two-pigment animals is because they aren't seeing as broad a spectrum? I didn't read the article that way, but you could be right. I assumed the spectrum was the same in all cases.

[I'm Murrin]

I read it as, they are able to make more nuanced distinction between the colours, because they have a photopigment with another range to compare with the first two.

[Xar]

Mice cannot see reds and greens because of the lack of the third photopigment. To them, the world is blues, yellows, and grays.

[Avatar]

Hmm, still immediate in the sense that the very first generation to have them demonstrated its ability to take advantage of it though.

--A

[Alynna Lis Eachann]

say, through virus-mediated gene transfer, or other such methods

How well does that actually work. I mean, I've seen it used in sci-fi but how realistic is it, really?

Also, sign me up for the UV/infrared vision... it would make bird identification soo much easier.

[Xar]

say, through virus-mediated gene transfer, or other such methods

How well does that actually work. I mean, I've seen it used in sci-fi but how realistic is it, really?

Also, sign me up for the UV/infrared vision... it would make bird identification soo much easier.

Well, virus-mediated gene transfer is used as a technique in several labs, including one just next to mine... We already know certain viruses are particularly good as vectors, so all that's left is to pack them with the desired DNA and inject them near the cells of interest. They'll take care of the rest, infecting the cells with the DNA and making sure it is transcribed, thus producing the protein. There are, however, drawbacks: depending on the size of the DNA, for example, you might need to use bigger viruses, which diffuse less, which in turn means you'd have to use more of them and do more injections. Additionally, I'm not sure about the viability of the technique from a long-term point of view; some of these viruses eventually kill the affected cells, so it's a rather delicate operation. Still, the technique exists, and it is improving as we speak.