Determination of the curvature of epithelial cell mass by mesenchyme in branching morphogenesis of mouse salivary gland

Mouse submaxillary epithelium undergoes branching morphogenesis with increase in the curvature of its surface in vivo. Recombination experiments in vitro of the epithelium and mesenchyme between 13- and 14-day rudiments showed (1) that the 14-day mesenchyme more actively induced the epithelium to branch than the 13-day mesenchyme, (2) that the 14-day mesenchyme could produce clefts on smaller epithelial lobes than the 13-day mesenchyme, (3) that the 14-day mesenchyme produced lobes with similar diameter to lobes of the 14-day intact rudiment, and (4) that the lobular morphology of assembled 14-day lobes became obscure in recombinates with the 13-day mesenchyme while it was well maintained in recombinates with the 14-day mesenchyme. From these results it is concluded that the mesenchyme determines the curvature of epithelial surface, and that clefts are formed on the epithelial surface as a result of increase in the epithelial curvature.