Mechanical aspects of the mesenchymal influence on epithelial branching morphogenesis of mouse salivary gland

Three activities of mesenchymes from mouse embryonic submandibular gland, lung, stomach, mandible and skin were comparatively studied. The first ability was the induction of branching of submandibular epithelial lobes. Epithelial lobes branched well in recombination with submandibular or lung mesenchyme, less well with stomach mesenchyme, but never with mandibular or dermal mesenchyme. The second behavioural aspect studied was the contraction of collagen gels. When respective mesenchymal cells were dispersed at 2á0×105cellsml-1 in collagen gels (1á5mgml-1) and incubated, dermal mesenchymal cells had the highest gel-contracting activity. The gel-contracting activity of submandibular or lung mesenchymal cells was two thirds as high as that of dermal cells and that of stomach or mandibular mesenchymal cells was much lower. The last activity was to separate three plastic beads that were recombined with mesenchymes in place of epithelial lobes. Salivary or lung mesenchyme effected a large separation of the beads, whereas dermal mesenchyme left beads contacting one another. There was a positive correlation between the branch- inducing activity and the beads-separating activity within the five kinds of mesenchymes. In time-lapse cinematography of recombinates, cells of submandibular and lung mesenchyme were observed moving (or flowing) around, and their property was different from that of dermal mesenchyme. In the presence of cytochalasins, both the contraction of collagen gels and separation of plastic beads by submandibular mesenchymal cells were completely inhibited. These results suggest the importance of mechanical influences of the mesenchyme in salivary branching morphogenesis.