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Eric Beyer, Peter Minogue, Helena Yu, Richard Schroeder, Joseph Snabb, Rebecca Zoltoski, Viviana Berthoud; Connexin50 mutation D47A impairs lens fiber cell differentiation and organelle degradation as well as causing cataracts. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3680.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations of the lens fiber gap junction proteins (connexins) have been linked to autosomal dominant congenital cataracts. Substitutions of Aspartate-47 (D47) of Cx50 have been identified in several different human pedigrees. To elucidate the lens abnormalities caused by a substitution at this position, we studied No2 mice which carry the Cx50D47A mutation and parallel the human pathology. Cx50D47A mice have cataracts that are much more severe in homozygotes than heterozygotes. Lenses of Cx50D47A mice are also smaller than those of wild type littermates.
Lenses from mice of different ages (neonatal to ≥4 months) were examined by dark field, scanning electron, and confocal immunofluorescent microscopy. Lens homogenates were studied by immunoblotting with primary antibodies directed against connexins, other membrane proteins, and proteins residing in different organelles.
In mutant animals, the levels of Cx50 were severely reduced as compared to those in wild type mice (<20% in heterozygotes and ≤3% in homozygotes). Cx46 levels were also decreased in mice carrying one or two Cx50D47A alleles, but to a lesser extent than Cx50. The mutant mouse lenses showed a loss of cell structure (especially in the nucleus), altered cell membrane morphology and a lack of fiber cell interdigitations, most severely in the homozygotes. The lenses of Cx50D47A mice showed the persistence of nuclei and the presence of abundant nuclear remnants in deep regions of the lens. Among organelle-specific proteins, levels of Histone-3 were very elevated. DNAse activity was not reduced (and therefore could not explain the persistence of nuclei). Aquaporin0 was severely reduced in homozygotes, while N-cadherin was increased.
Our data show that the expression of Cx50D47A leads to cataract formation which is likely due to a severe decrease in the abundance of functional connexin channels. They also implicate the mutant in impaired differentiation of fiber cells manifested by impaired degradation of some organelles and reduced levels of some fiber-cell specific proteins.
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