Epithelial-mesenchymal interface in the rat mandibular process observed by electron microscopy.

Abstract

Epithelial-mesenchymal interfaces in the stomodeal side of the rat mandibular processes were observed at Theiler's stages 14 and 15, when no epithelial organogenesis could be detected by electron microscopy. At stage 14, the basal lamina was discontinuous. Disintegrated basal lamina-like materials were seen in the epithelial-mesenchymal interface. A number of coated vesicles and smooth vesicles were seen in epithelial cell processes adjacent to the disintegrated basal lamina-like materials. Some epithelial cell processes penetrated into the mesenchymal space through the basal lamina and touched the ectomesenchymal cells. Other epithelial cell processes or satellite cell bodies protruded into the mesenchymal space, but were covered with basal laminae. At stage 15, the basal lamina was smooth and continuous with partial duplications. Ruthenium red-positive anionic sites were distributed in the basal lamina and on thin filaments underneath the basal lamina. At stage 15, the separation among anionic sites became more regular than that at stage 14. In this study we found some stage-specific morphological events in the epithelial-mesenchymal interface in the stomodeal side of the mandibular process at stages preceding the initiation of epithelial organogenesis.