The fate of epidermal desmosomes in mammalian skin

Summary

• 1. The fine structure of epidermal desmosomes and hemi-desmosomes has been studied in the different layers of the epidermis of anterior abdominal wall skin of guinea-pigs. The tissue was embedded in epoxy resins and the sections were stained with uranyl acetate.

• 2. In the basal layer, the stratum spinosum and in the deeper layers of the stratum granulosum the desmosomes had the same characteristic structure. Each consisted of localized areas of thickening of the cell membrane of two contiguous keratinocytes. As seen in section the total width of the desmosome was about 700–850 Å units. When cut tangentially the membrane thickenings were round or oval in shape and measured about 0.25–0.7 μ in diameter. In the intercellular interval between the thickenings and running parallel to them were situated three thin electron dense laminae. Converging to be attached to the intracellular surface of each thickening were bundles of tonofilaments. None of the tonofilaments crossed the intercellular space between the thickenings.

• 3. At the junction between the stratum granulosum and the stratum corneum the structure of the desmosomes changed. The cell membrane of the stratum corneum cell showed considerable overall thickening and the desmosomal thickening could no longer be identified. In many of the desmosomes the dense intercellular laminae were partly fused together and in some of them the process of fusion was complete. In the deeper layers of the stratum corneum the now fused laminae formed a single dense fusiform body between the apposed cell membranes. In the intermediate layers the solid bodies became enlarged and were oval in shape. In the superficial layers of the stratum corneum the interior of each body showed signs of breaking down leaving a well defined limiting membrane. In the region where exfoliation was occurring, the limiting membrane of the intercellular bodies degenerated and the vesicular structures ruptured.

• 4. Hemi-desmosomes were found on the part of the cell membrane of the keratinocyte adjacent to the basement membrane. Each consisted of a localized area of thickening of the cell membrane and a precisely apposed thickening of the basement membrane. Within the interval and lying close to the cell membrane thickening and parallel to it was a single thin electron dense lamina.

• 5. The dendritic cells of the epidermis were seen to be lying free between adjacent keratinocytes and the basement membrane, there being no desmosomes or hemi-desmosomes. The dendritic processes of these cells extended out between adjacent keratinocytes and insinuated themselves between adjacent desmosomes.

• 6. The functional significance of the desmosome and hemi-desmosome was considered. The relationship between the desmosome and its dynamic environment was discussed.