Differential expression of the epidermal K1 and K10 keratin genes during mouse embryo development

Induction of genes coding for the K1 and K10 keratins during mouse development was studied by measuring the accumulation of their respective mRNAs in day 10 to 17 embryos using an RNase protection assay. Although these two keratins are coexpressed in the suprabasal layers of the epidermis, it was found that while K1 mRNA was detectable as soon as day 10, K10 mRNA was not detectable before day 12. The expression of these genes at this stage of development was not expected since they are specifically associated with keratinization, a process that does not begin before day 17 of gestation. Histological examination of the epidermis of day 10 to 17 embryos suggests that both genes are induced in cells committed to epidermal differentiation, after stratification has started but before the onset of keratinization. It was also found that the two mRNAs increased in abundance steadily and significantly until day 16 and that, in spite of the expectation that filaments should contain equivalent amounts of each subunit, K1 mRNA remained more abundant than K10 mRNA at all times including in adult epidermis. These observations indicate that the two genes are regulated independently during development.