Expression of transglutaminase activity in developing human epidermis.

Epidermal transglutaminase (TGase) is known to catalyse cross-linking of several precursor proteins in the formation of cornified cell envelope at the terminal differentiation of keratinocytes. Expression of TGase activity was studied using an in situ TGase activity assay in human fetal skin samples of 49-163 days estimated gestational age (EGA). In the early two-layered epidermis (49-56 days EGA), in situ TGase activity was not observed in the periderm cells or the basal cells. In the late two-layered epidermis (57-65 days EGA), in situ TGase activity became weakly positive in the periderm cells, but not in the basal cells. In the three-layered (66-95 days EGA) and in four- or more layered (96-135 days EGA) stratified epidermis, in situ TGase activity was still restricted only to the periderm cells. After keratinization occurred in the interfollicular epidermis (163 days EGA), in situ TGase activity was expressed in the granular and cornified layers. This unique localization of TGase activity further support the hypothesis that periderm cells form cornified cell envelope during their regression process in human fetal skin development.