From the Labs: Biotechnology

Mice with Enhanced Color Vision
Mice engineered to have a third photoreceptor can distinguish more colors than normal mice

Source: “Emergence of Novel Color Vision in Mice Engineered to Express a Human Cone Photopigment”
Gerald H. Jacobs et al.
Science 315(5819): 1723-1725

Results: Researchers from Johns Hopkins University and the University of California, Santa Barbara, used genetic engineering to breed mice that have three kinds of photoreceptors, as humans do, instead of two, as mice normally do. After lengthy training, the mice were able to distinguish colors that normal mice could not.

Why it matters: Since the result required only genetically induced changes of the photoreceptors and no tweaking of the underlying neural circuitry, the findings suggest that the sensory system is very plastic and can learn to use entirely new information. This could explain how primates, the only animals with trichromatic color vision, developed their color-­sensing abilities. Primates may have taken advantage of the extra visual information granted by a new photoreceptor without evolving specialized wiring in the brain.

Methods: Researchers engineered mice to express the gene for a photo-sensing protein that can detect red light, which mice usually can’t distinguish from green. In behavioral tests, the mice were shown three ­circles of colored light–two of the same color and one of a different color distinguishable to humans but not to normal mice. After intensive training during which the mice were rewarded for selecting the different color, scientists found that mice with the extra sensor could tell the colors apart while their normal counterparts could not.

Next Steps: Researchers plan to investigate how the visual system in the engineered mice adapted to take advantage of the new information.

Source: “Proteorhodopsin ­Photo­system Gene Expression ­Enables Photophosphorylation in a ­Heterologous Host”
Edward F. DeLong et al.
Proceedings of the National Academy of Sciences 104(13): 5590-5595

Results: The common bacterium E. coli can be converted into a light-­harvesting organism in a single genetic step. MIT researchers modified the E. coli genome to include a string of DNA found in marine microörganisms that can generate energy from light. The resulting bacteria synthesized all the components necessary to duplicate that feat and assembled them in the cell membrane.

Why it matters: The genetically modified E. coli, which would normally derive their energy from organic compounds like sugars, were able to switch to a diet of sunlight. Similar modifications could lead to bacteria that more efficiently produce biofuels, drugs, and other chemicals, since they could use more of their carbon food sources as material for bioproducts rather than “burning” them for energy.

The findings also shed light on microbial evolution. Scientists had previously found that the genes for the light-harvesting system, which are often found grouped together in the genome, are frequently swapped among different microörganisms in the ocean. The fact that a single genetic transfer can provide cells with all the genes they need to harvest energy from light helps explain how that capacity could travel so widely. (The mechanism for converting light into energy described here, which was discovered just a few years ago, is different from chlorophyll-based photosynthesis.)

Methods: The genes inserted into the E. coli enabled them to synthesize two proteins: proteo­rhodopsin, which is similar to a protein found in the human retina, and retinal, a light-­sensitive molecule that binds to proteo­rhodopsin. When the proteo­rhodopsin is bound to retinal and struck with light, it pumps positively charged protons across the cell membrane. That creates an electrical gradient that acts as a source of energy.

Next Steps: The researchers are now working on ways to boost the modified bacteria’s ability to harvest and use energy from light.