Common transglutaminase substrates shared by hair, epidermis and nail and their function

The hair follicle contains several components with different programs of differentiation some of which include the synthesis of a cornified envelope. Our interest in cornified envelope precursors of the epidermis prompted an investigation of the location of several of these in the hair follicle. Monoclonal antibodies to the precursor proteins involucrin, pancornulin and sciellin were reacted with frozen section of skin and their localization detected by fluorescein tagged antibodies or the peroxidase technique. Staining was observed in the ostium and isthmus of the hair follicle using all 3 antibodies and was similar to that observed in epidermis. Staining of the inner root sheath was also observed with all 3 antibodies. In the case of the antibody to sciellin, the reaction was clearly localized to the cell periphery using special fixation. The other antibodies did not react by this technique and appeared to show cytoplasmic staining. Similar studies with nail also showed reactivity, but the distribution of the 3 proteins in the different regions of the nail varied. The role of the envelope precursors in the hair follicle remains to be established. The inner root sheath does not appear to have a fully developed cornified envelopes and isopeptide bond formation occurs primarily in the cytoplasm. These proteins may have a role similar to trichohyalin in cornification of the inner root sheath.