The ureteric bud (UB) develops from the Wolffian duct on E10.5, initiating kidney development. The metanephric mesenchyme (MM) produces signals that induce the formation and outgrowth of the UB. As the UB elongates, it begins to form two domains that differ in their gene expression patterns and developmental fates: the distal tip of the UB will begin to branch and give rise to most of the collecting system, while the tubular portion (trunk) of the initial UB will give rise to the ureter.