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Y. Zhang, D. J. Burgess, P. A. Overbeek, V. Govindarajan; Ras Activation Alters Lens and Corneal Differentiation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1138.
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© ARVO (1962-2015); The Authors (2016-present)
Our previous studies have shown that expression of fibroblast growth factor 10 (FGF10) in the murine lens induces the overlying corneal epithelial cells to proliferate initially, then to differentiate into lacrimal glands. The purpose of this study was to test whether Ras activation can phenocopy the effects of FGF10 stimulation of the corneal epithelial cells.
In order to activate Ras in the corneal epithelial cells, we have generated transgenic mice that express a constitutively active form of human H-Ras linked to a modified Pax6 promoter. This promoter is active in the lens, corneal and conjunctival precursors. Ocular development of wild type and transgenic mice was analyzed by standard histological techniques, in situ hybridization and immunohistochemistry.
Two transgenic families (OVE2043, OVE2044) that express the Pax6-Ras transgene were generated. Adult transgenic mice in the OVE2043 family appeared normal and in the 2044 family showed microphthalmia. Ras transgene expression was seen in the OVE2044 but not in the OVE2043 family. Histological analysis showed that the Ras transgenic mice did not develop ectopic lacrimal glands in the corneas. Instead, the lenses failed to detach from, and remained embedded in, the cornea. There were profound alterations to the corneal architecture; a distinctive corneal endothelial layer was absent and the stroma was disorganized. BrdU incorporation assays showed increased proliferation of lens and corneal epithelial cells with concomitant increase in cyclin D1 expression. Expression of keratin 12, a corneal epithelial differentiation marker, was downregulated in Ras transgenic corneas. In contrast, Ras transgenic lens epithelial cells showed upregulation of early fiber differentiation markers including Prox1, p27 and p57. Lacrimal glands, derived from conjunctival epithelial cells, showed an altered branching pattern in Ras transgenic mice.
These results taken together suggest that key events during ocular development including completion of lens invagination, proliferation and differentiation of lens and corneal epithelial cells and branching morphogenesis of lacrimal glands are sensitive to alterations in Ras-mediated signaling. Our results also imply that Ras activation is not sufficient to phenocopy the effects of FGF10 stimulation of the corneal epithelial cells and that FGF10-induced glandular differentiation requires activation of other signaling molecules in addition to Ras.
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