Intercellular contacts at the epithelial-mesenchymal interface of the developing rat submandibular gland in vitro

An ultrastructural study of the development of the rat submandibular gland (SMG) analage in vitro was undertaken to determine if epithelial-mesenchymal and epithelial-nerve contacts were integral events in the differentiation of the gland in vitro as they are in vivo. SMG rudiments were removed at the stalk-bulb stage (15 days in utero) and cultured for 6 days on a millipore filter in supplemented McCoy's 5A media. Rudiments were taken at daily intervals, fixed and processed for electron microscopy. The overall development of the explanted rudiments closely paralleled their maturation in vivo although cultured glands lagged 24-36 h behind their normal counterparts. Direct epithelial-mesenchymal contacts were seen after the morphogenetic patterning of the gland had been established but prior to functional differentiation of the rudiment. Epithelial-nerve contacts were not seen although healthy axons were seen in the stroma throughout the culture period. The study indicates that epithelial-nerve contacts are probably not required for morphogenesis of cytodifferentiation of the rat SMG. However, direct epithelial-mesenchymal contacts appear to be an integral part of the developmental sequence of the rat SMG.