KERATINIZATION OF AVIAN EPIDERMIS . AN ULTRASTRUCTURAL STUDY OF NEWBORN CHICK SKIN

The newborn chick skin was studied in the light and electron microscopes in an effort to obtain information about the differentiation products of epidermal cells and sequential events which lead to the formation of the horny layer. Filaments are relatively few in both basal and differentiating cells. The cytoplasm undergoes compartmentalization during cell differentiation, and specific products are formed sequentially within segregated areas. In the cortical part of the cytoplasm a fine filamentous network appears upon which keratohyalin is later deposited. In the central part of the cytoplasm numerous large lipid droplets are formed by participation of an agranular reticulum and the Golgi system. Many multigranular bodies are also formed which contain several lamellated granules. When the cells enter the horny stage, the nucleus and the synthetic organelles are decomposed, the plasma membrane thickens, and the cell content consists of lipid surrounded by a fibrous-amorphous mass. These observations indicate that the pathway of differentiation the chick epidermal cells follow is different from that seen in mammals, and the protective horny cells are both structurally and chemically different from those of other vertebrates. © 1969 Academic Press, Inc.