Genetic Engineering Color Vision in Mice
Genetic studies endow mice with new color vision
Although mice, like most mammals, typically view the world with a limited color palette – similar to what some people with red-green color blindness see – scientists have now transformed their vision by introducing a single human gene into a mouse chromosome. The human gene codes for a light sensor that mice do not normally possess, and its insertion allowed the mice to distinguish colors as never before.
In a study published in the March 23, 2007, issue of the journal Science, Howard Hughes Medical Institute researchers at Johns Hopkins, together with researchers at the University of California at Santa Barbara, demonstrated in a series of cleverly designed color vision tests that the genetic modification allows mice to see and distinguish among a broader spectrum of light waves. The experiments were designed to determine whether the brains of the genetically altered mice could efficiently process sensory information from the new photoreceptors in their eyes. Among mammals, this more complex type of color vision has only been observed in primates, and therefore the brains of mice did not need to evolve to make these discriminations.
The new abilities of the genetically engineered mice indicate that the mammalian brain possesses a flexibility that permits a nearly instantaneous upgrade in the complexity of color vision, say the study’s senior authors, Gerald Jacobs and Jeremy Nathans.
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“Our observation that the mouse brain can use this information to make spectral discriminations implies that alterations in receptor genes might be of immediate selective value not only because they expand the range or types of stimuli that can be detected but also because they permit a plastic nervous system to discriminate between new and existing stimuli,” the authors wrote in the Science paper. “Additional genetic changes that refine the downstream neural circuitry to more efficiently extract sensory information could then follow over many generations.”
I’m surprised that the mouse brain visual system is sufficiently plastic that the altered mice gained significant color differentiation ability.
Since it’s a function that’s so easy to turn on, does this suggest that trichromacy must in fact be disadvantageous to mice – at least those whose food sources are not signaled by colored lights?
There is a finite available space on the retina for cones. If there is a greater variety of cone types, then the packing density of any single cone type must be lower, and thus the spatial resolution for each color “channel” must be poorer. So trichromacy comes at a cost.
Right, of course, just a waste of resources for most mammals when what they need most visually is to see in the dark. Thanks.
This refutes an argument against evolution once made by Fred Reed. I was never impressed with that argument but it’s nice to see it decisively refuted.
Hm, does this mean we could insert a gene into humans giving us infrared and/or UV vision? I would totally go for that!
Nickelplate: “Hm, does this mean we could insert a gene into humans giving us infrared and/or UV vision? I would totally go for that!”
My guess is that gene engineering could be used to give humans IR or UV vision. However, as ChairmanK points out, there would be tradeoffs. Instead of gene engineering human vision I’d opt for electronically enhanced vision that improved resolution, contrast, and magnification or frequency shifting for IR or UV vision.
Most interesting to me is the demonstration of mammal brain plasticity. Adaptable brain processing might permit biological engineering for enhanced mental abilities such as expanded working memory.
Don’t think the retina will allow UV rays through, so that would be a little more complex. Maybe IR though.
Also, while your brain could process the signal, perhaps it is not ready for this info 24/7. Maybe it would become annoying?
Right, of course, just a waste of resources for most mammals when what they need most visually is to see in the dark. Thanks.
Does this mean color-blind humans have better night vision? Has that ever been tested?
Dave, I’m pretty sure it’s the lens that blocks UV. If a critter lives a long time, it’s best not to have high energy photons banging it’s delicate retinas around.
Yes it’s the lens that block the uv. I believe people who have had cataract surgery (and have artificial lenses) actually can see in the near uv.
I believe there’s only one kind of photoreceptor in the eye and the cones are just different kinds of filters. IR light isn’t high enough energy to excite it, so there’s no hope for an IR cone. But we it’s probably possible to make people tetrachromatic like birds by borrowing some genes from them.
Re: UV vision in birds
http://www.bio.bris.ac.uk/research/vision/4d.htm
“Bird colour vision differs from that of humans in two main ways. First, birds can see ultraviolet light. It appears that UV vision is a general property of diurnal birds, having been found in over 35 species using a combination of microspectrophotometry, electrophysiology, and behavioural methods. So, are birds like bees? Bees, like humans, have three receptor types, although unlike humans they are sensitive to ultraviolet light, with loss of sensitivity at the red end of the spectrum. This spectral range is achieved by having a cone type that is sensitive to UV wavelengths, and two that are sensitive to “human visible” wavelengths. Remember, because ‘colour’ is the result of differences in output of receptor types, this means that bees do not simply see additional ‘UV colours’, they will perceive even human-visible spectra in different hues to those which humans experience. Fortunately, as any nature film crew knows, we can gain an insight to the bee colour world by converting the blue, red and green channels of a video camera into UV, blue and green channels. Bees are trichromatic, like humans, so the three dimensions of bee colour can be mapped onto the three dimensions of human colour. With birds, and indeed many other non-mammalian vertebrates, life is not so simple. As well as seeing very well in the ultraviolet, all bird species that have been studied have at least four types of cone. They have four, not three, dimensional colour vision. Recent studies have confirmed tetra-chromacy in some fish and turtles, so perhaps we should not be surprised about this. It is mammals, including humans, that have poor colour vision! Whilst UV reception increases the range of wavelengths over which birds can see, increased dimensionality produces a qualitative change in the nature of colour perception that probably cannot be translated into human experience. Bird colours are not simply refinements of the hues that humans, or bees, see, these are hues unknown to any trichromat.”
Is the bird lens more transparent to UV than the human lens?
Re: UV and IR vision in butterflies
“Depending on the species, small butterflies have either apposition eyes or some similar type of eye optics. Butterflies of various colors and designs need to see a wide spectrum of colors in order to find food, survive and multiply. Butterflies may have up to four different pigments in their eyes, as compared to two or three in many other insects. As a result, some butterflies have wide-spectrum color vision allowing them to see UV light reflected from specific flowers. Others can also see near-infrared-light beyond human color vision limits. They seem to respond to image color more than image detail, but their eyes have enough resolution to see fine patterns in flowers, and to see other butterflies in order to fly together. Some butterflies can see 30 micron (.03mm) details on objects, while the human eye can see details only in the range of 100 microns (.1mm). One possible reason for this variation is the large difference in eye focal lengths. The butterfly’s eye, with short focal length, is able to focus closer than the human eye. Normally, human eyes can focus better at a longer distance, over a wider field, than butterfly eyes.”
Yes the lens. My bad.
Does this mean color-blind humans have better night vision? Has that ever been tested?
Daveg: What do you mean by “better night vision”? Do you mean the ability to detect photons at all in darkness? Or you do mean the ability to discriminate color in darkness? The ability to see forms and motion in darkenss is mostly mediated by rods, not cones.
This doesn’t answer your question, but David Williams’ group at U. Rochester has shown that color detection is not easily predicted from cone composition in the retina: Hofer, Singer, Williams (2005) Different sensations from cones with the same photopigment. J. Vis. 5:444-454.
Better night vision is the ability to see shapes and movement – anything that would help you find food or avoid being food. I would presume this means the ability to detect photons in the darkness, yes.
I guess the question is if the missing cones just replaced with cones of the other colors, or do you get more rods? Or perhaps photons of certain colors are more prevalent at night than others, and thus a preference of one color is better for night vision?
guess the question is if the missing cones just replaced with cones of the other colors, or do you get more rods?
I think that color-blind people have the same number pf cones as everyone else, but remember that vision is in the brain as well as the eyes. The mouse brains wired themselves so as to take advantage of the extra color receptors, presumably color-blind people’s brains make the neurons that would otherwise be used to distinguish between red and green available for other purposes. So maybe color-blind people are more sensitive to variations in shades of gray (or something) even without having any extra rods.