Molecular mechanism of ureteric bud development.

The urinary collecting system is derived from an epithelial protrusion arising from the Wolffian duct called the ureteric bud (UB) by the signal from its inductive tissue, metanephric mesenchyme (MM). Targeted gene mutation studies have shown that several transcription factors and MM-secreted glial cell line-derived neurotrophic factor (GDNF) are critical for initiation of the UB. After initiation, the UB undergoes branching morphogenesis. Results obtained from in vitro culture systems, including an isolated UB culture, together with gene mutation studies suggest that interplay of multiple positive and negative soluble factors as well as extracellular matrix (ECM) and matrix-degrading proteinases regulate branching morphogenesis.