The role of mesenchyme in the morphogenesis and functional differentiation of rat salivary epithelium.

SUMMARY The ability of foetal rat salivary epithelium, particularly from the parotid gland, to develop morphogenetically and functionally (amylase activity) in various mesenchymes, and the quantitative effects of altering mesenchymal mass on the development of the parotid epithelium, have been studied in vitro. Both parotid and submandibular epithelial rudiments were able to undergo morphogenesis and subsequent cytodifferentiation in their own and in the reciprocal mesenchyme. The growth of the explant and the arrangement of the acini were governed by the mesenchyme, submandibular mesenchyme supporting the development of more acini, which were more closely packed, than parotid mesenchyme. The functional product of the epithelium was not qualitatively affected, amylase activity being developed only by parotid epithelium, whether in its own or in submandibular mesenchyme. Amylase activity was greater when the epithelium from a single parotid rudiment was recombined with submandibular mesenchyme than with its own mesenchyme. Increasing the initial mass of either salivary mesenchyme also led to the development of more amylase activity. Parotid epithelium was able to develop in lung mesenchyme, but not so well as in its own mesenchyme. Stomach and pancreatic mesenchyme could support only limited histogenesis of parotid epithelium. The results are interpreted in terms of morphogenetic and growth control of salivary epithelium by mesenchyme, the subsequent cytodifferentiation of the terminal buds being typical of the organ from which the epithelium was derived.