Fig. 1. Expression of Six1 during kidney development analyzed by in situ and X-gal staining of heterozygous Six1^lacZ embryos for the Six1^lacZ allele. (A) In situ hybridization showing Six1 expression in metanephric mesenchyme (mm) at E10.5. (B) X-gal staining of Six1^lacZ heterozygous embryos showing strong Six1^lacZ expression at E10.5, similar to that observed by in situ hybridization (A). (C) At E11.5, Six1 is expressed in the induced mesenchyme (mm) around the ureteric bud epithelium (ur). (D) X-gal staining of E17.5 Six1^lacZ heterozygous kidneys showing Six1^lacZ expression in collecting tubules (arrow). Six1^lacZ is also expressed in the muscles surrounding the ureter (ur). (E,F) Transverse sections of X-gal-stained Six1^lacZ heterozygous kidneys at E17.5 revealed that the Six1^lacZ-expressing cells are localized in the collecting tubules (arrows). F is higher magnification of the boxed area in E. p, renal pelvis; wd, Wolffian duct.