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Dominic Cosgrove, Mei Tian, Wei-Min Wang, Marisa Zallocchi, You-Wei Peng; Photoreceptors in whirler mice show defective transducin translocation and are susceptible to light-induced degeneration. Invest. Ophthalmol. Vis. Sci. 2013;54(15):639.
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Usher syndrome combines congenital hearing loss and retinitis pigmentosa (RP). Mutations in the whirlin gene (DFNB31/WHRN) cause a subtype of Usher syndrome (USH2D). Whirler mice have inner ear defects but do not develop retinal degeneration. Here we investigate abnormalities in whirler mouse photoreceptors.
Immunohistochemistry, serial tangential section immunoblotting and hydroethidine-based detection of intracellular superoxide production were used. Photoreceptor cell densities under various conditions of light/dark exposures were evaluated.
In whirler mouse photoreceptors, the light-activated rod transducin translocation is delayed and its activation threshold is shifted to a higher level. Rhodopsin is observed in the connecting cilia of rods. Continuous moderate light exposure induced significant rod photoreceptor degeneration and superoxide accumulation. Whirler mice reared under a 1500 lux light/dark cycle also resulted in significant photoreceptor degeneration. Previously, we reported that shaker1 mice, a USH1B model, also showed moderate light-induced photoreceptor degeneration with delayed transducin translocation.
The results from shaker1 and whirler mice suggest that defective transducin translocation is linked to light-induced degeneration, and these two symptoms may reflect defects in rod photoreceptors. These results also indicate that both Usher syndrome mouse models may share a closely related pathobiological mechanism for retinal degeneration.
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