We then generated Spry1+/–; Spry2+/– mice either expressing Ret (RetEGFP/+) or not (RetEGFP/EGFP) and analyzed their caudal WDs by EGFP fluorescence at birth, since Ret-knockout animals die shortly after birth owing to renal agenesis (Fig. 6). This evidence concerns the gene RET and renal agenesis.