CORNEA-SPECIFIC EXPRESSION OF K12-KERATIN DURING MOUSE DEVELOPMENT

The full-length cDNA of mouse K12 keratin was characterized by sequenc ing overlapping cDNA clones isolated from a mouse cornea cDNA library. Using Northern blot hybridization, the radio-labeled cDNA hybridized to a 1.9 kb mRNA from adult cornea, but not from other mouse tissues i ncluding snout, esophagus, tongue, and skin. During mouse development, corneas do not express K12 mRNA until 4 days postnatal when the epith elium begins to stratify as judged by Northern blot and in situ hybrid ization. In situ hybridization with H-3-labeled cDNA probe and immunoh istochemical studies with antibodies against a synthetic oligo-peptide deduced from rabbit K12 cDNA demonstrate that this mouse K12 keratin is expressed in all cell layers of adult corneal epithelium, and the s uprabasal layers, but not the basal layer of the limbal epithelium. Ep idermal growth factor (EGF) has been shown to promote epithelium strat ification of cultured chicken and human corneas in vitro. To examine w hether EGF can promote K12 expression, EGF was administered to neonata l mice. The results indicate that EGF retards K12 expression by cornea l epithelial cells, even though it promotes corneal epithelial stratif ication during mouse development. Taken together, our results demonstr ate that the expression of K12 keratin is cornea-specific, differentia tion-dependent, and developmentally regulated.