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D. Chakraborty, M. I. Naash; Modulating the Amount of RDS and Rod-Opsin Affects Retinal Structure and Function. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1101.
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Overexpression and mislocalization of the rod visual pigment (rhodopsin) has been shown to cause retinal degeneration. In the absence of retinal degeneration slow (rds-/-), rods also degenerate and rhodopsin is mislocalized. Here we test the hypothesis that opsin mis-localization in the rds-/- retinas contributes to the rate of degeneration seen in the absence of RDS.
Double knockout mice were generated by cross-breeding rds-/- with rho-/- mice. Retinal morphology was assessed by light and electron microscopy (LM, EM). Electroretinography (ERG) was used to evaluate retinal function at postnatal day 30. Protein expression was verified by western blotting and RT-PCR. Immunohistochemistry (IHC) was used to determine the localization of Rom-1, RDS, Rhodopsin, and other OS-specific proteins.
No OSs were formed in the retinas of rho-/-, rds-/- and rho-/-/rds-/- in contrast to the well-ordered ones seen in WT animals. Inner segments were dilated in rho-/-/rds-/- mutant, and in contrast to our hypothesis, retinal degeneration in the double knock-out was accelerated compared to the rds-/-. One to two fewer rows of nuclei were observed in the outer nuclear layer of the rho-/-/rds-/- retinas. However, surprisingly, Rom-1 message and protein levels were substantially increased in the double knock-out retinas when compared to rds-/- retinas. We also observe rhodopsin mis-localization in the rho+/-/rds+/- retinas. Further studies toward understanding the mechanism of rhodopsin mis-localization in the rho+/-/rds+/- retinas are currently in progress.
Elimination of rhodopsin did not halt or reduce the severity of photoreceptor cell death in rho-/-/rds-/- mice when compared to rds-/-. On the contrary, it accelerated the rate of degeneration likely due to the additive affect of the absence of two essential membrane proteins for the outer segment morphogenesis. Rom-1 is usually undetectable in rds-/- buteliminating rhodopsin in the double knockout appeared to stabilize it. Abnormal accumulation and mis-localization of rhodopsin in rds-/- and rho+/-/rds+/- retinas may generate stress on the rod translational machinery, alleviation of which could enable increased levels of other proteins including Rom-1.
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