A dual role for involucrin in the epidermis-ultrastructural localization in epidermis and hair follicle in humans and transgenic mice.

Transgenic mice expressing human involucrin (hINV) have an abnormal hair coat appearance. To understand this phenotype, we used immunoelectron microscopy to examine hINV distribution in the hair follicle and epidermis. In human epidermis, hINV is first observed in the cytoplasm of spinous and granular layer cells. In transition cells, it is equally distributed between the cytoplasm and the nascent cornified envelope, while in the corneocytes it is largely cornified envelope-associated. In transgenic mice, the pattern of expression is similar except that much more antigen appears to be present. An important finding is the presence of hINV in hair follicle structures--low levels in the hair and high levels in the inner root sheath (IRS). The distribution of hINV is comparable in human and transgenic mouse follicles; however, much higher levels are observed in the mice. In contrast, hINV is not detected in cells of the outer root sheath (ORS). Thus, hINV is differentially expressed in two related and contiguous tissues, the epidermis and the ORS. Based on these results we conclude that hINV is a specific product of differentiated IRS cells that is localized at the cell envelope, suggesting a function as a cross-linked constituent of IRS cell envelope. These results suggest that hINV may have a dual role in epidermis, as a cross-linked structural protein in the epidermal corneocyte and the hair follicle IRS.