cDNA clones that correspond to the major keratin genes expressed in mouse epidermis, the 50-, 55-, 59-, 60- and 67-kd keratin genes, have been isolated and characterized. Several lines of evidence are presented which suggest that the expression of these keratin genes is coordinately regulated and dependent on the state of differentiation. The 50-, 55- and 60-kd keratin genes are mainly expressed in proliferating basal cells and the 59- and 67-kd keratin genes are preferentially expressed in differentiated cells (the suprabasal layers) within the epidermis. This highly regulated program of gene expression was found to be altered by the exposure of mouse skin to agents known to disrupt normal differentiation such as the tumor promoter, TPA. Furthermore, malignant epidermal tumors, which exhibit altered differentiation programs, do not express the differentiation-associated keratin genes. Analysis of amino acid sequence data for keratin subunits, deduced from nucleotide sequence of corresponding cDNA clones, revealed fundamental differences in the primary sequence of keratin subunits expressed at different states of differentiation that may alter the properties and function of keratin filaments containing these subunits. This sequence information has permitted the production of antisera that are monospecific for individual keratin subunits and can discriminate between benign and malignant tumors. To determine if common regulatory sequences are shared by keratin genes that are coordinately induced during differentiation, we have isolated genomic clones for the 59- and 67-kd keratyine and determined their nucleotide sequence. In order to facilitate the elucidation of mechanisms regulating the expression of this family of genes, we have developed an in vivo model system (vaginal epithelium) that permits the controlled induction of differentiation and kerating gene expression.
