Keratin 12 deficient mice with recurrent epithelial erosion

Purpose. Expression of K3/K12 keratin pair characterizes the cornea-type epithelial differentiations. To elucidate the role of keratin 12 in the maintenance of corneal epithelium integrity, we have created transgenic mice deficient in keratin 12 via gene target techniques. Methods. One allele of murine KrtI.12 gene was ablated in embryonic stem cells, ES14.1 via homologous recombination with a DNA construct in which the DNA elements of exons 2 through exon 7 of keratin 12 gene was replaced by a Neo-gene. The homologous recombinant ES cells were injected to mouse blastocysts and germ lines transgenic mice were obtained. The corneas of hemizygous and homozygous transgenic mice were characterized by clinical observations under stereo microscope, histology at light and eletron microscopy, immunohistochemistry, in situ hybridization, Northern hybridization and Western immunoblot analysis. Results. The hemizygous transgenic mice lacking one allele of Krt1.12 gene appear normal and do not develop any clinical manifestations, e.g., cornea epithetial defects. Homozygous transgenic mice lacking both alleles develop normally and suffer repetitive corneal epithelial defects. Histoligical examination did not reveal abnormality in corneal epithelium, i.e., number of cell layers, and hemidesmosomes and desmosome. The cornea epithelium does not express keratin 12 as judged by immunohistochemistry, Western immune blot analysis with epitope-specific anti-keratin 12 antibodies, and Northern hybridization with ³²P-labeled keratin 12 cDNA and in situ hybridization with anti-sense keratin 12 riboprobe. Conclusion. The presence of cornea-specific K3/K12 keratin pair is essential for the maintenance of corneal epithelium integrity.