Purchase this article with an account.
B.M. Tam, O.L. Moritz; Cross–Species Comparison of the Effects of the P23H Mutation on Rhodopsin Trafficking and Toxicity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):814.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The rhodopsin mutation P23H accounts for 30% of North American cases of RP linked to the rhodopsin gene. In cultured cells this mutation falls into the category of class II mutants, which cause rhodopsin to misfold and be retained in the ER, or retrotranslocated to the cytoplasm as aggresomes. However, some researchers have reported P23H rhodopsin localized to outer segments (OS) of photoreceptors. There have also been reports of rescue of degeneration by dark rearing. These results conflict with our studies of P23H rhodopsin in transgenic X. laevis. X. laevis P23H rhodopsin is expressed at very low levels, and found almost exclusively in the ER, consistent with a misfolded protein undergoing ER–associated degradation. To determine whether these differences could be due to species–specific differences in rhodopsin structure or photoreceptor trafficking mechanisms, we have examined the localization properties of P23H rhodopsins from four different species expressed in transgenic X. laevis photoreceptors.
The P23H mutation was introduced into the human, bovine, murine, and X. laevis rhodopsin cDNAs. All four versions of wildtype and P23H rhodopsins were expressed in transgenic X. laevis under control of the opsin promoter. Transgenic retinas were analyzed by confocal microscopy, and the toxic effects and expression levels of the rhodopsins were compared in 22 animals of each type using dot blot assays.
Wild–type rhodopsins from all four species were transported to the OS of X. laevis photoreceptors, and did not cause significant retinal degeneration. On average, X. laevis rhodopsin was expressed at higher levels than the other three species. P23H rhodopsins from all species were expressed at very low levels, were retained in the ER, and caused retinal degeneration. However, immunolabeling indicated variable trafficking of P23H rhodopsins to the OS. X. laevis P23H rhodopsin was almost undetectable in OS, but bovine P23H rhodopsin was easily detectable, and was expressed at significantly higher levels than the other three P23H rhodopsins. Human and mouse P23H rhodopsins were also found in somewhat greater quantities than X. laevis P23H in the OS by microscopy.
Regardless of species, the mutant rhodopsin P23H was expressed at dramatically reduced levels resulting from ER accumulation, suggesting an ER–associated mechanism is involved in retinal degeneration. However, the extent of rhodopsin transport to the OS was dependent on context. Future studies will determine whether this OS rhodopsin contributes to retinal degeneration.
This PDF is available to Subscribers Only