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R. Maddala, B. Chauhan, C. Walker, C. Morris, Y. Zheng, M. L. Robinson, R. A. Lang, P. V. Rao; Rac1 Conditional Knockout Mice Reveal a Crucial Role for Rac GTPase in Regulating Lens Fiber Cell Migration, Polarity, Suture Formation, and Lens Shape. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1217.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the involvement of Rac GTPase function in lens fiber cell migration, polarity, adhesive interactions and cytoskeletal organization during the lens development.
Rac1 GTPase lens conditional knockout (cKO) mice were generated using Rac1flox and Cre transgenic mice expressing the Cre recombinase at different developmental stages and in different regions of the lens. Embryonic, neonatal and postnatal lenses derived from the Rac1 cKO mice were characterized histologically, immunohistochemically and biochemically.
The Rac1 cKO mice derived from Le-Cre and MLR-10 transgenic mice, which express Cre in both the lens epithelium and fibers starting from embryonic day E8.75 and E10.5, respectively, exhibited defective lens integrity and a marked reduction in eye weight. The lenses of Le-Cre and MLR-10 Rac1 cKO mice revealed a predominant phenotype characterized by abnormal fiber cell migration and orientation, with the terminals of basal and apical fibers exhibiting a striking, outwardly projecting arrangement starting at day E15.5 and E17.5, respectively. The Rac1 cKO lenses derived from MLR-39 mice expressing Cre only in the lens fibers demonstrated a moderate reduction in eye weight with abnormal fiber cell migration starting from day 1. While Rac1 cKO lenses exhibited shape abnormalities and defective suture formation, fiber cell differentiation and epithelial proliferation were unaffected in such lenses. As well, Rac1 cKO lenses were characterized by defective actin cytoskeletal organization concomitant with increased G-actin levels and cofilin phosphorylation, decreases in levels of phospho-paxillin, arp2/3, WAVE2 and spectrin staining, and alterations in distribution of cell adhesive molecules including β-catenin, N-cadherin, Abi, Rap1 and Nectin. The levels of integrins including αvβ1, β3, and β5 were markedly reduced in the Rac1 cKO mouse lenses.
The Rac1 cKO mouse lenses demonstrate dramatic abnormalities of organization and migration of fiber cells, and defective suture formation in association with disrupted actin polymerization and cell adhesive interactions. These findings support a vital role for Rac1 GTPase in regulation of lens fiber cell migration, cytoarchitecture, shape, polarity, and adhesive interactions.
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