Generation and Characterization of a Novel Mouse Line, Keratocan-rtTA (Kera(RT)), for Corneal Stroma and Tendon Research

PURPOSE: We created a novel inducible mouse line Keratocan-rtTA (Kera(RT)) that allows specific genetic modification in corneal keratocytes and tenocytes during development and in adults. METHODS: A gene-targeting vector (Kera- IRES2-rtTA3) was constructed and inserted right after the termination codon of the mouse Kera allele via gene targeting techniques. The resulting Kera(RT) mouse was crossed to tet-O-Hist1H(2B)-EGFP (TH(2B)-EGFP) to obtain Kera(RT)/TH(2B)-EGFP compound transgenic mice, in which cells expressing Kera are labeled with green fluorescence protein (GFP) by doxycycline (Dox) induction. The expression patterns of GFP and endogenous Kera were examined in Kera(RT)/TH(2B)-EGFP. Moreover, Kera(RT) was bred with tet-O-TGF-α to generate a double transgenic mouse, Kera(RT)/tet-O-TGF-α, to overexpress TGF-α in corneal keratocytes upon Dox induction. RESULTS: Strong GFP-labeled cells were detected in corneal stroma, limbs, and tail when Kera(RT)/TH(2B)-EGFP mice were fed Dox chow. There was no GFP in any single transgenic Kera(RT) or TH(2B)-EGFP mouse. Histological analysis showed that GFP in the cornea was limited to stromal keratocytes of Kera(RT)/TH(2B)-EGFP, which is consistent with Kera expression. Induction of GFP occurred in 24 hours and reached a plateau by 7 days after Dox induction. GFP could be detected 3-months after induction of Kera(RT)/TH(2B)-EGFP. Ectopic expression of TGF-α in corneal keratocytes caused hyperplasia in the corneal epithelium and stroma. CONCLUSIONS: The novel Dox inducible Kera(RT) driver mouse line is a useful genetic tool for gene manipulation and elucidating gene functions in corneal stroma and tendons of limbs and tail during embryonic development, homeostasis and pathogenesis.