Cytochemistry of trichohyalin granules: a possible role for cornification of inner root sheath cell in the hair follicle.

Abstract

We studied ultracytochemically how trichohyalin granules (TGs) were involved in the cornification of the inner root sheath (IRS) cells in the hair follicle. After storing unfixed mouse skin samples in glycerol and then low ionic strength salt solution (G-LISS), the TGs reduced electron-dense amorphous material (EDM) to various degrees, with the appearance of filamentous material in routine staining. As the IRS cells were differentiating, these changes in the TGs became successively prominent; Some TGs consisted of the filamentous material and residual granular EDM, showing a "filamentogranular structure". In the cells in transition to cornified cells, or transitional cells, the EDM of the TGs disappeared and consisted of only filamentous material which was intertwined with keratin filaments (KFs). The internal substructure of the TGs induced by the G-LISS treatment stained well with ethanolic phosphotungstic acid, which reacts with basic proteins, and the KFs associated with the TGs also stained well. In skin samples not treated with G-LISS, the TGs of the transitional cells often exhibited fibrogranular structure after PTA staining to detect tissue basic proteins, suggesting a release of PTA stainable proteins(s) by the TGs in living transitional cells. The KFs of the cornified cells were more intensively stained and thicker (about 20 nm wide) than those of the differentiating IRS cells. These findings suggest that the TGs may contain at least two kinds of basic proteins; One is G-LISS-soluble, and the other is a very insoluble filamentous protein. These protein materials may be added to or incorporated into the KFs in the cornified cells with the disappearance of the TGs, since the KFs are markedly thick with PTA staining.