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Jutta U. Schlegel, Dorothee Röll, Martin Bergmann, Birgit Lorenz, Knut Stieger; Characterization of a humanized Mouse-Model for X-linked Retinitis Pigmentosa caused by a point mutation in the Rpgr gene. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6451.
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Point mutations in the gene encoding the retinitis pigmentosa GTPase regulator (RPGR) are responsible for X-linked Retinitis pigmentosa (XLRP) in humans. Over 80% are found in a specific, repetitive region of the terminal exon ORF15, which is therefore called the mutation hot spot of RPGR. Point mutations cause a frame shift, thus modifying the C-terminal amino acid chain and potentially causing a toxic gain of function of the altered protein. In this work we characterised a transgenic mouse model containing a point mutation in the murine ORF14/15 similar to those causing XLRP in human patients.
Animals were euthanized at different time points and morphological analysis of the retinae was performed using Hematoxilin and Eosin stained paraffin sections, and toluidine blue stained semithin sections. In addition, epon blocks were generated for electron microscopy. Immunohistochemical examination of opsin localization was performed with S, L/M, and rod opsin specific antibodies. To assess the biochemical properties of the protein, isoelectric-focusing in combination with western blot analysis was performed using mouse RPGR specific antibodies.
Morphological analysis revealed alterations in the inner segments (IS) and outer segments (OS) as well as in the nuclear layer of photoreceptors of affected animals as early as 4 weeks of age. OS were disorganized and of round shape, while IS were thickened in comparison to the wild-type photoreceptor. The outer limiting membrane was less well visible in affected retinae and the Connecting Cilium was of abnormal structure. Photoreceptor disorganisation increased progressively. Immunohistochemical examinations showed alteration of opsin localisation. The biochemical properties of the altered RPGR protein shifted as expected by biometrical calculations.
The newly generated mouse model exhibits a retinal pathology, which suggests a disease-progression similar to the one found in human XLRP patients. In the future this model will allow us to gain insight into the pathological mechanisms responsible for the degeneration as well as the biochemical causes for the toxicity of the altered protein. Furthermore, it will serve as a suitable animal model in the development of gene therapeutic strategies.
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