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Aaron Daniel Loewen, Beatrice M Tam, Colette N Chiu, Orson L Moritz; Characterization of adRP-associated rhodopsin missense mutations in transgenic Xenopus laevis rod photoreceptors. Invest. Ophthalmol. Vis. Sci. 2019;60(9):434.
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Over 150 rhodopsin mutations have been associated with autosomal dominant retinitis pigmentosa (adRP); however, the relationship between many of these mutations and their cell death mechanism is unknown. Patient data has separated rhodopsin mutations into two categories: class “A” mutations such as E181K and G89D exhibit a uniform and severe RP phenotype, while class “B” mutations such as D190G and P23H exhibit a less severe phenotype with later onset of RP. While these mutations have been identified in patients, the consequences of mutated rhodopsin in rod photoreceptor cells are unclear. We investigated adRP-associated rhodopsin missense mutations and their effects on rhodopsin localization in rod photoreceptor cells as well as retinal degeneration (RD).
We microinjected human rhodopsin transgenes into wild-type Xenopus laevis eggs. The human rhodopsin was either wild-type or contained base-pair changes resulting in missense mutations previously associated with adRP. Tadpoles were raised in cyclic light for 14 days. The eyes were enucleated for either fixation or solubilisation. Fixed eyes were cryosectioned and labeled for mammalian rhodopsin and imaged using a confocal microscope. Solubilised eyes were used in a dot blot analysis that probed for either mammalian or total rhodopsin.
We have created several novel transgenic X. laevis models of adRP based on rhodopsin mutations, including E181K and D190G. Mutations showed differential localization of rhodopsin within the photoreceptors, accumulating in the rod outer segment and/or the rod inner segment to varying extents. As well, varying levels of RD were noted between the mutations analysed ranging from severe RD to no RD present.
Variability of rhodopsin localization suggests that mutations play different roles in adRP pathogenesis through the activation of different cell death pathways. Mutations displaying predominantly inner segment retention of rhodopsin may be undergoing ER stress, which leads to cell death. Outer segment localization of rhodopsin may point to a photoactivation-dependant pathogenic pathway. Some rhodopsin mutations were previously considered to be pathogenic but, lacking sufficient pedigree data, may not be pathogenic. Our transgenic X. laevis models may provide a useful means of identifying disease mechanisms associated with large numbers of rhodopsin mutations.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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