Connexin 50-R205G Mutation Perturbs Lens Epithelial Cell Proliferation and Differentiation.

Purpose: To investigate the underlying mechanisms for how the mouse Cx50-R205G point mutation, a homologue of the human Cx50-R198W mutation that is linked to cataract-microcornea syndrome, affects proper lens growth and fiber cell differentiation to lead to severe lens phenotypes. Methods: EdU labeling, immunostaining, confocal imaging analysis, and primary lens epithelial cell culture were performed to characterize the lens epithelial cell (LEC) proliferation and fiber cell differentiation in wild-type and Cx50-R205G mutant lenses in vivo and in vitro. Results: The Cx50-R205G mutation severely disrupts the lens size and transparency. Heterozygous and homozygous Cx50-R205G mutant and Cx50 knockout lenses all show decreased central epithelium proliferation while only the homozygous Cx50-R205G mutant lenses display obviously decreased proliferating LECs in the germinative zone of neonatal lenses. Cultured Cx50-R205G lens epithelial cells reveal predominantly reduced Cx50 gap junction staining but no change of the endoplasmic reticulum stress marker BiP. The heterozygous Cx50-R205G lens fibers show moderately disrupted Cx50 and Cx46 gap junctions while the homozygous Cx50-R205G lens fibers have drastically reduced Cx50 and Cx46 gap junctions with severely altered fiber cell shape in vivo. Conclusions: The Cx50-R205G mutation inhibits both central and equatorial lens epithelial cell proliferation to cause small lenses. This mutation also disrupts the assembly and functions of both Cx50 and Cx46 gap junctions in lens fibers to alter fiber cell differentiation and shape to lead to severe lens phenotypes.