Mesenchyme specificity in rodent salivary gland development: the response of salivary epithelium to lung mesenchyme in vitro.

Lung mesenchyme is able to support budding and cytodifferentiation of salivary epithelial rudiments in vitro. No difference in response was found between submandibular and parotid epithelium from mouse or rat. There are several further features of this result, which is contradictory to previous findings. (.1) Lung mesenchyme is quantitatively less effective than submandibular mesenchyme for supporting submandibular morphogenesis. At least part of this difference is attributed to the inability of submandibular epithelium to replace lung epithelium in supporting the growth of lung mesenchyme. (2) Rat lung mesenchyme is quantitatively more effective than mouse lung mesenchyme when recombined with mouse submandibular epithelium. This may be at least partly due to mouse lung being more easily damaged by the procedures used. (3) Whereas the response of submandibular epithelium to submandibular mesenchyme is equally good on an agar or Millipore filter (MF) substratum, the response to lung mesenchyme is severely reduced or eliminated on MF. This difference is interpreted in terms of different mesenchymal cell densities necessary for submandibular or lung mesenchyme to support branching morphogenesis. Salivary buds formed in lung mesenchyme after 6 days are smaller and more closely packed than in salivary mesenchyme. In these heterotypic recombinates, the accumulation of amylase-resistant, PAS-positive material in the buds is initially accelerated and the tubular epithelium accumulates glycogen.