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LW Reneker, PA Overbeek; Ras-signaling is Essential for Lens Growth and Development . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3880.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Ras-mediated signal transduction pathways are essential for cell proliferation in most cell types. The purpose of this study is to investigate the role of Ras in lens growth and development using transgenic mice. Methods: We examined the expression patterns of the lens endogenous Ras genes (H-, K- and N-Ras) by in situ hybridization. To make the transgene express in both lens epithelial and fiber cells, we modified the mouse αA-crystallin promoter by adding the chick δ-crystallin enhancer element at the 5' end of the αA-promoter. Using this modified promoter, we generated transgenic mice expressing either a constitutive active or a dominant negative mutant of Ras in the lens. The effects of Ras mutants on lens development were analyzed by histology, immunohistochemistry and in situ hybridization. Results: During normal development, lens expresses all three Ras genes, but predominantly N-Ras. The expression level of N-Ras correlates with the lens growth rate. To investigate whether Ras activation is sufficient to induce lens cell proliferation, we established twelve lines of transgenic mice expressing a constitutive active H-Ras mutant (Rasac) in the lens. In situ hybridization showed that the transgene is expressed in both lens epithelial and fiber cells. At embryonic day 12 (E12), the Rasac transgenic lens is much bigger and contains 2-3 times more bromo-deoxyuridine (BrdU) positive cells compared to the non-transgenic lens. Cyclin A, D and E are upregulated in the Rasac transgenic lenses. To test whether lens cell proliferation requires Ras activity, we have generated 3 lines of transgenic mice expression a dominant negative Ras mutant (Rasdn) in the lens using the modified αA-crystallin promoter. Transgenic mice from two lines develop microphthalmia and have smaller lenses. The total lens cells in the Rasdn lenses are significantly reduced. Conclusion: Activation of Ras-signaling pathways is not only sufficient to induce lens cell proliferation but also essential for normal lens growth and development.
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