Salivary gland morphogenesis: possible involvement of collagenase.

When 12-day rudiments of mouse submandibular glands were cultured, they formed an average two clefts within 24 h. The average number of the clefts, however, increased up to five in the presence of bovine tissue inhibitor of metalloproteinases (TIMP). Contrary to this, either bacterial or bovine interstitial collagenase in the medium completely inhibited the cleft formation of the glands. Electron microscopic observations revealed that the amounts of collagen bundles at the cleft points significantly increased with TIMP, but decreased with bacterial collagenase. These results strongly support the idea that endogenous collagenase regulates the cleft formation through the modulation of fibrillar architectures containing collagen in the extracellular matrix. Recently, our immunohistochemical studies clarified that collagen III, known to be rich in embryonic tissue, accumulated preferentially at the cleft points of the epithelium, and may play a crucial role in submandibular gland morphogenesis.