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L.W. Reneker, L. Xie; Sprouty2 (Spry2) Provides a Control Mechanism for Cell Proliferation During Lens Development . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1096.
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Sprouty (Spry) proteins have been implicated as negative regulators of receptor tyrosine kinease (RTK)–signaling pathways. Members of the Spry gene family are expressed in the lens, especially in lens epithelial cells. Previously, we demonstrated that Spry2 overexpression in the lens of transgenic mice can lead to inhibition of cell proliferation which results in a smaller lens. The purpose of this study is to elucidate the essential role of Spry2 in lens cell proliferation and differentiation by knocking down the endogenous Spry activity.
A Spry2 mutant which carries a tyrosine to phenylalanine mutation at position 55, Spry2Y55F, functions as a dominant negative form in vitro. We constructed a minigene by linking the Spry2Y55F cDNA to the ΔEnαA chimeric promoter which contains the chicken Δ1–crystallin enhancer fused to the mouse αA–crystallin promoter. Transgenic mice were generated by pronuclear microinjection. Changes in lens morphology and lens cell behavior in the transgenic mice were analyzed by histology, immunohistochemistry and in situ hybridization.
Six transgenic lines expressing Spry2Y55F mutant in the lens were established. The severity of the phenotypes varies from mild cataracts to microphthalmia and correlates with the expression levels of the transgene. In the severely affected lines, the anterior epithelium of the lens is multi–layered with excess cells forming a subcapsular mass at the germinative zone. The epithelial defects in the lens of the Spry2Y55F mice resembles those found in the transgenic mice that overexpress growth factor PDGF–A in the lens. Bromodeoxyuridine (BrdU) incorporation assay showed that cell proliferation was significantly enhanced in the Spry2Y55F transgenic lenses. When taken together, these results suggest that the role of Spry2 is to negatively regulate the level of cell proliferation during lens development. In other words, by knocking down the endogenous Spry2 activity with a dominant negative mutant, we increased cell proliferation in the lens of the Spry2Y55F transgenic mice.
The data from the Spry2Y55F transgenic mice are consistent with our hypothesis that Spry2 functions as a negative regulator of cell proliferation, potentially contributing to the establishment and maintenance of the monolayer structure of the lens epithelium.
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