A cone opsin double knockout mouse reveals long-term cone survival and provides a platform for gene therapy.

Mutations in cone opsin-encoding genes are associated with colorblindness and retinal disease. In certain forms of blue cone monochromacy (BCM) in humans, a viable cone population that does not express cone opsin is present in the retina. Double cone opsin knockout (DKO) mouse models of BCM have been developed previously using gene trap insertion in one or both opsin genes. Here, we report and characterize a new mouse line that completely lacks both short-wavelength (S) and middle-wavelength (M) sensitive cone opsin genes but maintains a viable cone population to one year old. DKO mice experienced approximately a 30% reduction in cones between 4 and 12 months, similar to the age-related decline in wild-type controls, and did not show signs of retinal degeneration. This mouse will be useful for the development of cone opsin gene therapies directed at treating BCM, in which the expression of L and M opsin is lost, but many cones remain as potential gene therapy targets. It also has implications for understanding the survival of cones without opsin, which differs from the fate of rods without rhodopsin.