Abstract
The ease of genetic manipulations makes the mouse ideal for investigating the effects of human L cone opsin mutations on photoreceptor structure and function. In the mouse retina, cones expressing UV opsin form a gradient with fewer than 500/mm2 in dorsal retina, increasing to 10,000/mm2 in ventral retina. Cones expressing M opsin exhibit a gradient in the opposite direction. In the zone between dorsal and ventral retina, nearly all cones coexpress both M opsin and UV opsin, and some authors have reported that all mouse M cones coexpress UV opsin. To study the effects of human cone opsin mutations on photoreceptors it is essential to have exclusive expression of one opsin gene per cone. We created a UV opsin knockout mouse by deleting 3 exons of the mouse UV opsin gene. The deletion was confirmed by sequencing. Immunohistochemistry demonstrated an absence of cones labeling with the anti-UV opsin antibody, molecular methods demonstrated an absence of UV opsin messenger RNA, and the electroretinogram with a UV cone isolating stimulus demonstrated the absence of functional UV cones. We also created a targeted gene replacement replacing the endogenous mouse M opsin gene by a human L opsin gene. The targeted replacement was confirmed by direct sequencing of the altered genomic locus, by molecular methods, and by the flicker photometric electroretinogram. Our ultimate goal is to cross knock-in/knock-out mice carrying mutant L opsins to UV knock-out mice to study the effects of L opsin mutations on photoreceptors in UV opsin knockout mice.
Research supported by NEI Grant R01 EY009620.