An ultrastructural study on the rôle of the keratohyalin granules in the keratinization process

Abstract

Electron staining with phosphotungstic acid added to the alcohol used for the dehydration and combined with the staining of ultrathin sections with uranyl acetate or nitrate gives a high contrast-effect of different structures of Araldite-embedded skin. This investigation consists of an electron microscopic study of keratohyalin granules in normal epidermis of guinea pigs. The cytoplasm of stratum granulosum becomes progressively looser in texture as it approaches the skin surface. The tonofilament bundles in this layer show a low contrast, and seem to be split up and reduced in number. They are oriented around the keratohyalin granules. In the entire non-cornified epidermis are observed particles about 100–250 Å in diameter and arranged in groups. In stratum granulosum they are found around the keratohyalin granules. The latter are of different shapes and sizes and are scattered over the whole cytoplasm. They seem to grow through the incorporation of tonofilaments and the above-mentioned particles. Transitional cells (T-cells) between stratum granulosum and stratum corneum have been demonstrated in the dorsal and foot skin of guinea pigs. In dorsal skin they appear singly. Their cytoplasm is mainly filled with keratohyalin granules. Around these are seen groups of particles, apparently in close contact with the granules. The keratohyalin granules in granular and T-cells show a pattern. This is assumed to represent a precursor state in the development of the keratin pattern. The cell boundaries of T-cells show high opacity and a width of about 150 Å. The intercellular space between granular, T- and cornified cells contains a well-stained amorphous material in which vesicles are dispersed.