Keratin gene expression in mouse epidermis and cultured epidermal cells.

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Abstract
The major differentiation products of mouse epidermis are keratins of 40-70 kilodaltons (kDal). A library of c[complementary]DNA clones was prepared from total poly(A)+ RNA from newborn mouse epidermis. Clones corresponding to the major in vivo keratins of 55, 59 and 67 kDal were isolated and characterized. By RNA blot analysis of poly(A)+ RNA from newborn mouse epidermis, RNA species were identified that are approximately 1600, 2000 and 2400 nucleotidies in length and are complementary to the cDNA for the 55-, 59- and 67-kDal keratins, respectively. Analysis of RNA from primary cultures of newborn mouse epidermis by this same technique shows greatly reduced levels of these RNA. Transcripts complemetnary to all 3 cloned cDNA are abundant in 14-16-day embryonic and adult mouse skin. Altered expression in cluture does not appear to be due to induction of a developmentally programmed switch by placing the cells in culture but instead is due to factors modulating expression within the culture system. Because the 55-, 59- and 67-kDal keratins are the major proteins in epidermis they probably represent keratin associated with terminal differentiation. Cultured cells are apparently blocked in expression of differentiation keratins but instead synthesize other keratin family members probably related to cytoskeletal functions.