Formation

of the definitive (metanephric) kidney depends on tightly regulated reciprocal

interactions between two embryonic tissues. The ureteric bud arises as an

outgrowth from the mesonephric (Wolffian) duct and undergoes repeated branching

to form the collecting duct system, renal pelvis, calyces, and ureter. At the

same time, the surrounding metanephric mesenchyme must receive appropriate

signals from the ureteric bud in order to differentiate into nephrons. Failure

of either tissue to form or interact properly leads to predictable structural

defects in kidney development.

In

an experimental model, signalling pathways required for initiation of the

ureteric bud are selectively disrupted on the