ROBO2 and hydronephrosis: To determine if there is a causal relationship between VUR and hydronephrosis and if the process of hydronephrosis formation in Robo2 adult mice is active or a residual effect of antenatal hydronephrosis, we performed ultrasound-guided percutaneous aspiration of the unilateral hydronephrotic kidney in three Robo2 mosaic mutant mice (Fig. 5A–C, Video S5 and Video S6).