Identification of keratins 3 and 12 in corneal epithelium of vertebrates.

Keratins form the intermediate filaments in almost all epithelial cells in vertebrates. The keratins of the rabbit corneal epithelium have previously been shown to be composed of a major keratin pair, formed by an acidic keratin K12 and a basic keratin K3, together with a minor keratin pair (acidic K14 and basic K5). Using electrophoretic and immunological analyses with two monoclonal antibodies, AK12 and AE5, that are monospecific for K12 and K3 respectively, we showed that the acidic keratin K12 is highly conserved throughout all the species studied except the trout, whereas the basic keratin K3 shows interspecies variations and was unequivocally identified only in mammals. Furthermore, in dog and human cornea K3 is present in small amounts compared with K12, while in mouse it is undetectable, suggesting that, in those species, the acidic keratin K12 may interact with the basic keratin K5 to form the corneal intermediate filaments.