OPSIN LOCALIZATION AND RHODOPSIN PHOTOCHEMISTRY IN A TRANSGENIC MOUSEMODEL OF RETINITIS-PIGMENTOSA

The VPP mouse is a transgenic strain carrying three mutations (P23H, V 20G, P27L) near the N-terminus of opsin, the apoprotein of rhodopsin, the rod photopigment. These animals exhibit a slowly progressive degen eration of the rod photoreceptors, and concomitant changes in retinal function that mimic those seen in humans with autosomal dominant retin itis pigmentosa resulting from a point mutation (P23H) in opsin. In th e present study we attempted to determine whether the disease process prevents the translocation of mutant opsin to the rod outer segments o f transgenic mice, and whether it affects the photochemical properties of the rhodopsin present within their rod outer segments. Immunocytoc hemistry with a monoclonal antibody against a region of the C-terminus that recognizes epitopes common to both normal and mutant opsin (mono clonal antibody-1D4), and a polyclonal antibody that reacts preferenti ally with the mutant opsin (anti-VPP), were used to identify the opsin present in the rods of three-week-old VPP mice and normal littermates . Absorbance spectra; photosensitivity, and regeneration kinetics of r hodopsin in rod outer segment disc membranes were analysed by spectrop hotometry. Western blot analysis with anti-VPP antibody indicated the specific binding of this antibody to the mutant opsin. Immunolocalizat ion with monoclonal antibody-1D4 and anti-VPP antibodies suggested a n ormal translocation of the mutant protein to the outer segments. Aside from a small disparity in the absorbance spectra of rhodopsin obtaine d from normal and VPP retinas, there were no significant differences i n either the ability of opsin to bind 11-cis retinal chromophore, or i n the photic sensitivity of rhodopsin. The results indicate that mutan t opsin is translated and incorporated into the rod outer segment disc membranes of VPP mice, and that the photochemical properties of rhodo psin in the rods of VPP retinas are similar to those of rhodopsin in n ormal retinas. (C) 1998 IBRO. Published by Elsevier Science Ltd.