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Sarah Mona El-Khazendar, Rebecca K Zoltoski, Viviana M Berthoud, Peter J Minogue, Eric C Beyer; Expression of a mutant Cx46 leads to changes in lens fiber ultrastructure. Invest. Ophthalmol. Vis. Sci. 2014;55(13):731.
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© ARVO (1962-2015); The Authors (2016-present)
Inherited human cataracts have been linked to mutations in connexin46 (Cx46) including Cx46fs380. Mice expressing Cx46fs380 were generated by a knock-in strategy. Although lenses of young mutant mice appear transparent, anterior cataracts were evident in homozygous Cx46fs380 mice at 2 months and in some heterozygotes at 4 months. The experiments were designed to characterize the structural changes in lens fiber cell membranes that occur in these mice with age.
Levels of connexins in lens homogenates were determined by immunoblotting. Lenses were examined by scanning electron microscopy, and the number of furrows, interdigitations, and ball and socket joints were quantified in different regions of the lenses from wild type and homozygous mice. Data are presented as mean ± SEM. Nonparametric t-tests were used to assess the significance of differences between genotypes and ages (p <0.05).
Levels of Cx46 were severely reduced in lenses from 1-month-old mutant mice, whereas Cx50 was only moderately decreased. In older lenses, reductions in Cx50 became more severe. At 1.3 months of age, fiber cell membranes of lenses from all three genotypes were structurally similar. With age, wild type lenses had increased furrows, as would be expected. When compared to wild type mice, lenses from 5.5 month-old homozygous mice showed a significant decrease in the number of furrows (34.6 ± 6.2 vs.14.7 ± 4.6, p=0.022) and interdigitations (8.9 ± 0.6 vs. 4.7 ± 1.2, p=0.022). No change in the number of ball and socket joints was detected (51.4 ± 1.7 vs. 52.4 ± 6.6, p=0.79).
Reductions of Cx46 and Cx50 precede the appearance of structural changes in lens fiber cell membranes and cataracts in Cx46fs380 mice. The remodeling of lens fibers during normal growth results in increased presence of both furrows and interdigitations. The decreased numbers of furrows and interdigitations in fiber cell membranes suggest that Cx46 mutations might alter the normal compaction process.
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