Effects of Excess FGF7 on Development and Differentiation of Corneal Epithelial Cells

Abstract

Purpose: : To investigate the effect of fibroblast growth factor 7 (FGF7) during mouse development and in adults with a binary inducible Krt12–rtTA/tetO–FGF7 bitransgenic mice, which over–express FGF7 in a corneal epithelium–specific manner upon induction by Doxycycline.

Methods: : A Krt12–rtTA mouse line was created by inserting an IRES–rtTA minignene into the Krt12 allele of mouse genome by knock–in strategy of gene targeting technique. The Krt12–rtTA mice were cross bred with tetO–FGF7 mice to obtain Krt12–rtTA/tetO–FGF7 bitransgenic mice. Expression of human FGF7 (hFGF7) was induced by the administration of doxycycline (Dox) via drinking water and chow. Histological analysis was performed to determine the consequences of excess FGF7 in corneas of Krt12–rtTA/tetO–FGF7 mice and control littermates.

Results: : Administration of Dox from fertilization caused corneal hypertrophy at birth (P0) in bitransgenic mice. Furthermore, 21 day–old (P21) bitransgenic mice with full–time Dox administration showed neovascularization and further hyperproliferation in corneal epithelium and stroma. Without Dox treatment, no pathology was observed at birth in the bitransgenic neonatals. Meanwhile, administration of Dox to single transgenic Krt12–rtTA and tetO–FGF7 mice did not show hyperproliferation in the corneal epithelium in the experimental mice. The 2–3 month–old adult bitransgenic mice induced by Dox administration showed increase number of cell layers in corneal epithelium in a time dependent manner. This corneal epithelium anomaly vanished and returned to normal morphology in two weeks after removal of Dox from the diet.

Conclusions: : Our results demonstrate that the Dox inducible system is effective in regulating transgene expression in corneal epithelium of Krt12–rtTA/tetO–FGF7 bitransgenic mice. Over expression of FGF7 caused corneal hypertrophy and the severity of pathology depending on the length and period of Dox treatment.

Keywords: cornea: epithelium • transgenics/knock-outs • development