Transgenic mice expressing Cre-recombinase specifically in M- or S-cone photoreceptors.

PURPOSE To establish lines of transgenic mice that express Cre-recombinase in M- or S-cone photoreceptors for generating cone photoreceptor-specific (conditional) mutants. METHODS Five kilobases of 5' upstream sequence of the mouse red-green (M) opsin gene or 0.5 kb of the mouse blue (S) opsin gene was cloned into a Cre-expression plasmid. Transgenic mice were generated and characterized, and appropriate lines were established. The Cre-transgenic mice were crossed with ROSA26-lacZ mice (containing floxed beta-galactosidase gene) and analyzed to determine Cre-recombinase activity. RESULTS Immunofluorescence study showed successful targeting of Cre-recombinase expression to cone photoreceptors. Double staining with anti-Cre antibody and anti-M- or anti-S-opsin antibody revealed specificity of Cre expression in M-opsin- and/or S-opsin-positive photoreceptors. Mating with ROSA26-lacZ mice demonstrated that Cre-recombinase was functionally active in M- or S-cones. CONCLUSIONS Lines of transgenic mice that specifically express functional Cre-recombinase in M- or S-cones were established in this study. Because mutations in several widely expressed genes lead to photoreceptor degeneration, these transgenic mice should be valuable in generating conditional mutants to investigate the function of various genes specifically in cone photoreceptors.