wmISH of Ret gene expression in wild-type and Wnt5a knockout mouse embryos. a, d At E11.5, the UB forms at the metanephric region and starts to branch in the wild-type embryo. b, e In some Wnt5a knockout embryos, the regions containing Ret-expressing IM are limited, the site of UB outgrowth occurred at the medial region and the branching is delayed. c, f In other Wnt5a knockout embryos, there are additional UB outgrowth sites. At E15.5, some Wnt5a knockout embryos developed unilateral kidney hypogenesis (i), while others have duplex kidneys/ureter (j).