Embryology of the epidermis: ultrastructural aspects. 1. Formation and early development in the mouse with mammalian comparisons.

A detailed light and electron microscopic study of the cellular morphology of developing epidermis in the 7 to 12 day mouse embryo reveals that a single layer of ectoderm is not present until day 8. The 8-day embryonic epithelium is characterized by the presence of microvilli, apical attachment specializations, developing desmosomes and a thin, immature basal lamina. The 9-day embryonic epithelium is flatter and has both an increased number of microvilli on the surface and an increased number of microtubules in association with developing desmosomes. On day 10, numerous developing desmosomes are associated with fine filaments in the regions of the attachment plaques. Occasional peridermal cells are present on day 11. Numerous granules are associated with the inferior cell membranes of the superficial or uppermost cell processes. In the 12-day embryo, the periderm forms a complete layer. A skein of fine filaments is present just inside the basal cell membrane of the germinative cells and microtubules are more abundant in the basal cell cytoplasm.