Differentiation markers in fetal epidermis: transglutaminase and transpeptidase

Two members of the transpeptidase family of enzymes, transglutaminase and gamma glutamyl transpeptidase, were assayed histochemically and biochemically in developing rat epidermis from day 15 of gestation through postnatal day 5. Electron microscopic examination of serial skin biopsies enabled precise dating of fetal epidermis and periderm and correlation of ultrastructural details of the cells with marker enzyme activities. Transglutaminase activity appeared histochemically in surface epidermis and in hair follicle inner root sheath on day 18 and day 21 of gestation, respectively, concomitant with the onset of terminal keratinization in these tissues. Enzyme activity was biochemically detectable 2 days before the histochemical stain became positive. Transpeptidase was active in fetal epidermis prior to keratinization but was only detectable in basal cells thereafter. Subsequent to birth, enzyme activity rose geometrically in hair follicles undergoing initial differentiation, and was thereafter found in all anagen hairs. Transglutaminase is active only in cells approaching terminal keratinization, while transpeptidase is associated with early phases of epidermal proliferation and differentiation.