Fig. 4. Six1 is required for the expression of Sall1 in the metanephric mesenchyme (mm). (A,B) Bmp4 is normally expressed in the mesenchyme around the ureteric stalk (ub) and its expression was not affected in Six1^-/- embryos at E10.5. (C,D) Bmp7 is normally expressed in the ureteric bud (ub) and metanephric mesenchyme at E10.5 and its expression levels are normal in both structures in Six1^-/- embryos at E10.5. However, its expression domain is reduced in size in Six1^-/- metanephric mesenchyme (D). (E,F) Wt1 is widely expressed in the mesenchyme and urogenital ridge region during kidney development and its expression level is not affected in Six1^-/- embryos at E10.5. However, its expression domain in the metanephric mesenchyme also appears to be reduced in size in E10.5 Six1^-/- embryos. (G,H) Sall1 is expressed in the metanephric mesenchyme before and after induction, however its expression was undetectable in the mesenchyme in Six1^-/- embryos at E10.5 (arrows). (I,J) Gdnf is expressed in the metanephric mesenchyme and its expression levels are normal in Six1^-/- embryos at E10.5. However, its expression domain appears to be reduced in size in Six1^-/- embryos at E10.5 (arrows).