When Spry1 is absent there is no brake on signaling via FGFR2 (Figure 10C), and GDNF can be removed without causing renal agenesis, due (at least in part) to the effects of FGF10, and to the restoration of Etv4/Etv5 expression; however, UB branching pattern is abnormal. Here, SPRY1 is linked to renal agenesis.