Glial Cell–Derived Neurotrophic Factor–Independent Ureteric Bud Outgrowth from the Wolffian Duct

The kidney collecting duct system and the ureter derive from the ureteric bud, an outgrowth of the Wolffian duct. It is generally believed that glial cell–derived neurotrophic factor (GDNF) plays a critical role in this earliest stage of kidney development, but 30 to 50% of knockout mice that lack