WT1 and Wilms tumor: Because the Nes-Cre and Pax8+/Cre drivers result in Wt1 loss immediately before and after the nephron MET, respectively, we reasoned that if disturbance of the MET is indeed important in the formation of Wilms' tumours (Hastie, 1994), characteristics of the tumours might already be found in these E18.5 mutant kidneys.