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Kannan Kunchithapautham, Beth Coughlin, Rosalie K. Crouch, Bärbel Rohrer; Cone Outer Segment Morphology and Cone Function in the Rpe65−/−Nrl−/− Mouse Retina Are Amenable to Retinoid Replacement. Invest. Ophthalmol. Vis. Sci. 2009;50(10):4858-4864. doi: 10.1167/iovs.08-3008.
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purpose. RPE65, a major retinal pigment epithelium protein, is essential in generating 11-cis retinal, the chromophore for all opsins. Without chromophore, cone opsins are mislocalized and cones degenerate rapidly (e.g., Rpe65 −/− mouse). Function, survival, and correct targeting of opsins is increased in Rpe65 −/− cones on supplying 11-cis retinal. Here, we determine the consequences of 11-cis retinal withdrawal and supplementation on cone development in the all-cone Nrl −/− retina.
methods. Rpe65 −/− Nrl −/−, Nrl −/−, and wild-type mice were examined. Cone structure was analyzed by using TUNEL assay, electron microscopy, and cone-specific antibodies. Cone function was assessed with light-adapted single-flash ERGs.
results. Rpe65 −/− Nrl −/− mice had an increased number of TUNEL-positive photoreceptors during programmed cell death compared with Nrl −/− mice, in addition to accelerated age-related degeneration. Cone function in Rpe65 −/− Nrl −/− mice was minimal, and opsins were mislocalized. Treatment with 11-cis retinal restored cone function, promoted outer segment formation, and enabled opsin trafficking to outer segments. Eliminating Rpe65 prevented rosette formation in Nrl −/− retinas; supplementation of Rpe65 −/− Nrl −/− mice with 11-cis retinal resulted in their reoccurrence.
conclusions. Taken together, function and opsin trafficking in Nrl −/− and wild-type cones are comparable, confirming and extending our findings that cone maturation and outer segment development are dependent on the presence of chromophore. The data on age-related cone death in Rpe65 −/− Nrl −/− mice and the reintroduction of rosettes after 11-cis retinal injections confirm that outer segments, which for steric reasons appear to introduce rosettes in an all-cone retina, are essential for cell survival. These results are important for understanding and treating chromophore-related cone dystrophies.
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