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Tami P. Bogea, Beatrice M. Tam, Orson L. Moritz; Ultrastructural Investigations of P23H-Light Induced Retinal Degeneration in a Xenopus laevis Model of Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5346.
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We previously observed that retinal degeneration in Xenopus laevis tadpoles expressing the bovine form of P23H mutant rhodopsin (bP23H) can be completely rescued by dark rearing. In the present study, we investigated the effects of light on photoreceptor ultrastructure of X. laevis tadpoles expressing bP23H.
Transgenic tadpoles expressing bP23H under the control of the X. laevis rod opsin promoter were generated and dark-reared until 14 days post-fertilization. They were then transferred to cyclic light and euthanized at various time points. Eyes were subsequently processed for quantitative rhodopsin dot blots, confocal microscopy, and transmission electron microscopy.
Rod outer and inner segments obtained from dark-reared tadpoles were comparable to those observed in wild type retinas. After 2 hours of light exposure, however, we observed the presence of whorls of disk membranes in the rod outer segments. After 36 hours, retinal degeneration became severe: we detected short rod outer segments and most whorls were surrounded by phagosomes and melanosomes in the retinal pigment epithelium. In addition, rod inner segments displayed endoplasmic reticulum vacuolization.
Our results indicate the presence of defects in both the outer and inner segment membranes of bP23H expressing photoreceptors. These defects appear as early as 2 hours after exposure to cyclic light. They are consistent with the instability of bP23H rhodopsin in both outer segments and the biosynthetic pathway upon light exposure. We intend to extend these ultrastructural investigations to include comparisons with other X. laevis models of retinitis pigmentosa.
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