ELECTRON MICROSCOPIC STUDY OF THE EFFECT OF VITAMIN A ON THE DIFFERENTIATION OF RECONSTRUCTED EMBRYONIC CHICK SKIN

In reconstructed embryonic chick skin, the mass of epidermal cells was separated from the mesenchymal portion by a continuous basallamina. The findings on the cytoplasmic organelles, e.g. filamentous structures, desmosomes, keratohyalin, and membrane coating granules of the peripheral and central epidermal cells, corresponded to those of the epidermis when the centre of the cell-mass was presumed to he the surface of the epidermis. The addition of 5 i.u./ml. vitamin A in the culture medium inhibited the process of keratinization. Filamentous structures and desmosomes were sparse even in the centre of the epidermal cell-mass. There were wide intercellular spaces and the basal lamina was obscure and discontinuous. The endoplasmic reticulum was dilated and the Golgi zones were distinct. Thus the vitamin A-treated cell resembles the secretory cell and shows less tendency to differentiate towards a keratinocyte. The development of lysosomes in the vitamin A-treated cells confirmed that vitamin A releases protease.