Tissue-specific inactivation of Osr1 in the cap mesenchyme causes premature differentiation. (A-F) Immunofluorescent detection of Six2 (green) and pan-cytokeratin (red) in developing kidneys of Osr1c/+;Six2-TGCtg (A,C,E) and Osr1c/-;Six2-TGCtg (B,D,F) embryos at E11.5 (A,B), E12.5 (C,D) and E13.5 (E,F). Arrows in F indicate abnormal mesenchymal aggregates in Osr1c/-;Six2-TGCtg kidneys. Scale bars: 100 μm. (G-J) Whole-mount immunofluorescence detection of Cited1 (green, G,H) or Jag1 (green, I,J) and pan-cytokeratin (red) in cultured kidney explants. Arrows in J indicate ectopic Jag1 expression in the CM distal to the UB tips. Insets in the lower right-hand corners of I and J show higher magnification pictures of the respective boxed region. Scale bars: 200 μm.