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Q. Liu, A. Saveliev, E. A. Pierce; Rp1-Q662X Knockin Mice Reveal Production of Truncated Rp1 Proteins and Develop Disorganized Outer Segments. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4648.
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© ARVO (1962-2015); The Authors (2016-present)
RP1 mutations account for 5-10% of adRP. The pathogenesis of the RP1 form of adRP is not completely understood. All pathologic mutations in RP1 found to date are predicted to result in premature termination of translation in the RP1 protein. The nonsense mutation, Arg677ter, is the most commonly observed mutation in patients with RP1. To elucidate the function of RP1 in vision and the mechanism by which mutations in RP1 lead to photoreceptor cell death, we used gene-targeting techniques to produce mice with a Q662X point mutation in Rp1 gene, which mimics the common Arg667Ter mutation found in RP1 patients.
The Rp1-Neo-Q662X gene targeting vector was produced using modified recombineering methods. Rp1-Neo-Q662X mice were generated using standard techniques. The Frt-flanked neomycin selection cassette was removed by crossing the Rp1-Neo-Q662X mice with universal FLPe deleter mice. Heterozygous Rp1-Q662X mice were intercrossed to generate homozygous mice. Western blotting and immunostaining were performed to detect expression of the mutant Rp1-Q662X protein in the retina. Retinal morphology and function in the mutant Rp1-Q662X mice and littermate controls were assessed by light and electron microscopy and ERGs.
Southern blotting and PCR analyses demonstrated that the Rp1 locus was successfully targeted in 2 ES cell clones. The truncated Rp1-Q662X protein containing the N-ternimal 662 amino acids (~74kDa ) was detected with anti-N-Rp1 antibodies from 1 and 5 month old mutant mouse retinas. This truncated protein was localized correctly to the axoneme of photoreceptor outer segments.Mice homozygous for the mutant Rp1-Q662X allele underwent a rapid-onset retinal degeneration characterized by incorrectly oriented outer segment discs that failed to stack properly into outer segments at the earliest examination point of P10. The rod ERG response in 1-month old mutant mice was reduced by approximately 60%. In contrast, the photoreceptors of heterozygous mice remained relatively healthy at 5-month-old of age.
We have generated point mutation Rp1 knockin mice that mimic the most common RP1 mutation in patients. The mutant Rp1-Q662Xallele produces a truncated N-Rp1 protein, confirming the hypothesis that RP1 mutations in patients result in the production of truncated versions of the RP1 protein in their retinas. The photoreceptor degeneration observed in the homozygous Rp1-Q662Xmice suggests the truncated N-Rp1 is non-functional. The Rp1-Q662X mice will be a useful model for testing therapeutic strategies to prevent visual loss from RP1 disease.
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