The synthesis of specific proteins in adult mouse epidermis during phases of proliferation and differentiation induced by the tumor promoter TPA, and in basal and differentiating layers of neonatal mouse epidermis.

Mouse epidermis can be induced to undergo sequential waves of proliferation and keratinization by treatment with the tumor promoter TPA (12-O-tetradecanoyl-phorbol-13-acetate). This model system offers a unique possibility to study the synthesis of differentiation-specific proteins in the epidermis. During these studies it could be shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis that several previously undetected proteins appear in the epidermis during the phase of differentiation. These have been fractionated according to solubility in 1 M phosphate buffer, pH 7.0, or 0.1 M sodium citrate buffer, pH 2.6. Of the soluble proteins, a band of approximate molecular weight 13,500 (band 1) appears early during the differentiative phase (24 hr after treatment with TPA). Another previously undetected protein of approximate molecular weight 27,000 (band 2) appears in the soluble fraction after 48 hr, at a time when many of the typical manifestations of increased keratinization can be observed. Both of these soluble proteins, although not detectable in normal adult mouse epidermis, are shown to be present in newborn mouse epidermis, which demonstrates histologically a well-developed layer of keratinizing and cornified cells. In addition, by separation of neonatal and TPA-treated adult mouse epidermis into "basal" and "cornified" layers, it could be demonstrated that these two proteins are localized exclusively in the upper layer of the epidermis.