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Charles B. Wright, Micah A. Chrenek, Jeffrey H. Boatright, John M. Nickerson; Differing Pathologies of Two Mouse Models of Leber Congenital Amaurosis, Type 2 (LCA2). Invest. Ophthalmol. Vis. Sci. 2011;52(14):2363. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Rpe65 knockout (KO) and rd12 mice, although both reported as null mutants, differ in visual phenotype. Rd12 mice experience a faster rate of visual function loss than Rpe65 KO mice, potentially suggesting the mutation in rd12 mice has extra toxicity. This study aims to help determine the rd12 the possible mechanism of action for the extra toxicity of the rd12 mutation.
The visual acuity and retinal function of C57BL/6J, Rpe65 KO, rd12, and rd12 heterozygote (het) mice were assessed by optokinetic tracking (OKT) and electroretinography (ERG), respectively, from P30 to P180. Ocular sections in paraffin were observed at 20X magnification on an inverted microscope. Rpe65 gene expression in C57BL/6J, Rpe65 KO, and rd12 mice was measured with qRT-PCR. Western blotting was performed on protein extracts from C57BL/6J, Rpe65 KO, and rd12 mice. Data were analyzed with analysis of variance (ANOVA) with post-hoc Student Newman-Keuls testing.
C57BL/6J mice maintained a constant visual acuity between P30 and P180, rd12 and Rpe65 KO mice completely lost visual acuity by P120 and P210, respectively. Rd12 het mice had slightly reduced visual acuity compared to C57BL/6J mice at P30. ERG measurements indicate rd12 het mice do not have reductions in a- or b-wave amplitude in comparison to C57BL/6J mice but do exhibit a slight reduction in oscillatory potential (OP) amplitudes at dim, but not bright, flash intensities. Retinal morphology is preserved in both Rpe65 KO and rd12 mice at P60. Rd12 mice have a significant reduction in axial length compared to C57BL/6J and Rpe65 KO mice. qRT-PCR shows 250-fold reduction in Rpe65 transcript in rd12 mice compared to C57BL/6J at P30 suggesting a truncated Rpe65 fragment is possible.
Visual acuity reductions in rd12 and a slight reduction in rd12 het mice as compared to Rpe65 KO and C57BL/6J mice, respectively, suggests the rd12 mutation has a possible additional toxic effect. ERG responses support OKT results. qRT-PCR suggests the rd12 mice expresses Rpe65 at a very low level. Production of a transcript at a low level may mean a low-abundance toxic Rpe65 protein fragment exists in rd12 mice.
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