A new study has revealed that mice that have been engineered to produce a human protein in their eyes develop dramatically enhanced color vision. For the study, a single human gene was introduced into a mouse chromosome. This enabled the mouse to distinguish more colors, a function that is invisible to rodents under normal circumstances.
Researchers at the Howard Hughes Medical Institute at John Hopkins together with researchers at the University of California at Santa Barbara demonstrated in a series of 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.
These new abilities in the genetically engineered mice show that the mammalian brain possesses a flexibility that permits a nearly instantaneous upgrade in the complexity of color vision, said Gerald Jacobs and Jeremy Nathans, the study’s senior authors.
“What we are looking at in these mice is the same evolutionary event that happened in one of the distant ancestors of all primates and that led ultimately to the trichromatic color vision that we now enjoy,” Nathans said.
For those who are unaware, trichromacy is dependent on three types of photoreceptor cells in the retina that preferentially absorb lights at different wavelengths. These are known as cone cells and each type contains a particular kind of light-absorbing sensor protein.
Basically, short-wavelength-sensitive cone cells are most sensitive to blue lights; medium-wavelength-sensitive cone cells are most sensitive to green lights and long-wavelength-sensitive cones are most sensitive to red lights.
So, when light strikes the retina and activates the cone cells, the brain compares the response of the S,M and L receptors, and it is the brain’s assessment of their relative levels of activation that we actually perceive as color.
John Mollon at the University of Cambridge has suggested that the evolution of trichromacy could have permitted primates to discriminate between unripe fruit, which is typically green, and ripe red- and orange-colored fruits.