Figure 2.

Working model for some of the events underlying branching morphogenesis. Ureteric bud branching morphogenesis is controlled by signals (both promoting and inhibiting branching) from the metanephric mesenchyme and probably other signals within the epithelium. The receptors trigger intracellular signaling pathways, which lead to changes in gene expression, as well as transcription-independent changes in the cell. Some of the cellular responses that may underlie branching (i.e., changes in the shape of the epithelium) are listed.