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A. Mitra, Y. Chinchore, P. J. Dolph; Genetic and Molecular Characterization of a Rhodopsin Mutant Causing Retinal Degeneration in Drosophila. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2288.
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Retinitis Pigmentosa (RP) is a disease caused due to genetic mutation(s) in the components of the visual cascade, which results in a gradual loss of vision in humans. A majority of the mutations, which cause RP in humans, are due to mutations in the light sensing opsin, Rhodopsin. In Drosophila, as in humans, rhodopsin mutations express a similar phenotype of progressive loss of photoreceptor neurons. The signal transduction pathways mediating photoreceptor loss are not known. Elucidation of the pathway(s) will shed light on the underlying mechanism(s) and offer insight into potential therapeutic targets to preserve photoreceptor structure and function. In this study, a rhodopsin mutant designated as R15 has been used.
In this study, thin sectioning was used to assay for photoreceptor structure and integrity. Immunostaining and confocal microscopy was used to determine localization of rhodopsin. Standard biochemical techniques were employed to ascertain the biochemical characteristics of the rhodopsin mutant.
Mutant rhodopsin expression causes loss of solubility of wild type rhodopsin, a significant amount of which is not degraded by the cell. Mutant rhodopsin is not trafficked properly to the rhabdomere where the phototransduction machinery is localized in the Drosophila photoreceptor. In the presence of mutant rhodopsin, wild type rhodopsin trafficking is also compromised and mislocalizes to the cell body. Our data suggests that the R15 mutant may be a representative of class II rhodopsin mutants, which form cytoplasmic protein aggregates and/or are sequestered in the endoplasmic reticulum (ER).
Expression of mutant rhodopsin exerts a dominant effect in the photoreceptor as it interferes with the normal trafficking of wild type rhodopsin in the photoreceptor. Rhodopsin mis-localization in the cell body suggests that it is may be stuck in the endoplasmic reticulum (ER) or in the cytosol as large molecular size insoluble protein aggregates where it induces cell death by yet unknown signaling pathway.
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