Desmosomes, Filaments, And Keratohyaline Granules: Their Role In The Stabilization And Keratinization of The Epidermis

Abstract

Components of desmosomes, filaments, and keratohyaline granules were studied by electron microscope and biochemical methods to clarify their role in the stabilization and keratinization of the epidermis. Isolated desmosomes are composed of 76% protein, 17% carbohydrate, and 10% lipid. The bulk of protein consists of a "spectrin"-like fibrous protein, presumably present in the plaque, and of glycoproteins in the desmosomal interspace. The main component of filaments, prekeratin, is a low-sulfur alpha-protein composed of a pair of three-chain subunits with non-alpha-helical segments separated by 200 A-long alpha-helical regions. The major component of isolated keratohyaline granules, the amorphous particulate material, is formed by a high-sulfur protein with a single-type of polypeptide chain. Polypeptide chains comparable to those found in prekeratin and keratohyaline granules were recovered from extracts of horny cells. Within the living part of the epidermis, filaments hypothetically form a cytoskeletal system which is anchored to desmosomes by a filamentous plaque protein. Glycoproteins are involved in the formation of strong junctions between the cells which enable the living part of the epidermis to respond as a whole to mechanical stress. The stratum corneum is stabilized by a similar system in a consolidated state which is less extensible. Horny cells are enveloped by a thickened membrane and the interfilamentous spaces are filled with various proteins including the sulfur-rich amorphous protein found in keratohyaline granules.

Visualization of a system of filaments 7-10 nm thick in cultured cells of an epithelioid line (Pt K2) by immunofluorescence microscopy.

“…4a) and show a variety of bizarre branchings and interconnections. They resemble the arrays described by Brecher in Pt K1 cells (8) and also the tonofilaments and prekeratin fibrils present in various epithelia, especially epidermis (11,12,18,21). The filaments in Pt K2 cells differ from microfilaments not only by their greater diameter, but also in other properties.…”

“…They further exhibit a conspicuous tendency to aggregate laterally and form ;tudies in indirect imheavily stained spicule-or rod-like bundles in which the indi-16), H17 serum gives vidual fibrous constituents are no longer distinguishable ( Fig. n the cytoplasm and 4), a situation which closely resembles the fibril-keratohyalin serum is used on 3T3 granule associations during early steps of keratinization procemid, colchicine, or cesses (11,12,18,21). Like the fibrous bundles of keratinizing )und the nucleus are epithelia, the 7-to 10-nm filaments of Pt K2 cells also show ese bundles increases frequent associations with clusters of ribosomes, probably higher concentrations polyribosomes (Fig.…”

“…1, 2, and 8 and other references in these papers). Other examples of such filaments include the neurofilaments of nerve cells (9,10), the tonofilaments of epithelial cells, and the prekeratin fibrils of keratinizing cells (11,12). All these filaments have diameters of 7-10 nm (10).…”

Isolation and characterization of desmosome-associated tonofilaments from rat intestinal brush border.

“…The material isolated consists almost exclusively of tangles of tonofilaments, many of which are connected to residual structures of the desmosomal plaques and of the terminal web and are enriched in cytokeratins. We have not yet been able to identify possible constituent proteins of the desmosomal plaque proper, similar to the relatively large polypeptides described for isolated desmosomes from bovine muzzle epidermis by Skerrow and Matoltsy (10,60,61) . The relationship of the proteins found in high salt-extracted apical tonofilaments from intestinal cells to the ethylenediamine-extractable protein associated with tonofilaments of rat epidermis (62) also remains an open question .…”

Peridermal granules of the chick embryo. Histochemical, ultrastructural and immuno-electron microscopical study.

“…However, Parakkal and Matoltsy (1968), Wong (1974) and Matoltsy (1975) showed that keratohyaline granules were amorphous and round matrixes with high density. Since we were not able to find such structures in the peridermal layers, the peridermal granules might be different from keratohyaline granules.…”