Mutation of Wt1 resulted in GR agenesis. WT1 (brown signal) was expressed in the coelomic epithelium and mesenchyme of the urogenital ridge from E9.5 (A, arrows) and continually expressed in somatic cells during gonad development (B-D). In control embryos, the GR arose as a thickening of the monolayer epithelium along the coelomic surface of the mesonephros from E9.5 and developed into gonads at E12.5 (A-D). The coelomic epithelium was present at E9.5 (E) in Wt1R394W/R394W embryos, but further development was arrested (F-G, arrows), and no gonads were observed at E12.5 (F). ce, coelomic epithelium; gr, genital ridge; md, mesonephros duct; g, gonad; k, kidney. Scale bars: 50 μm.