Morphogenesis and ultrastructure of the mouse embryonic salivary gland in tissue culture. Normal, and following exposure to trypsin.
The primordial submandibular glands of 12-day-old mouse embryos were studied in tissue culture before and after treatment with trypsin under the electron microscope. In vitro differentiation proceeded normally and reached a high level of differentiation. Following a soak in trypsin for 15 or 30 minutes, considerable changes were noted in the basal lamina and in the mesenchymatous cells. There often occurred bizarre bullous protrusions of the cytoplasm through the apparently weakened basal lamina and the mesenchymatous cells were converted into so-called "ropalocytes". Subsequently the cells regained their normal appearance and the basement lamina was covered by a thick layer of amorphous electron-opaque basement membrane like material. It is concluded that the basal lamina (the basement membrane under the light microscope) might be the keystone in the differentiation of an organ and its maintenance in the adult. The development of innervation has also been studied and it was shown that the developing submandibular galnd is endowed with large bundles of nerve axons surrounded by Schwann cells lying in the epithelial-mesenchymal region. Intra-epithelial nerves were conspicuous and occasional synaptic bars or rings could be seen contributing to thedifferentiation of the secretory cell.