Fig. 5. Timing of apoptosis and loss of nephric gene expression in Odd1 mutant embryos. Odd1 heterozygous (A,C,G) and homozygous null (B,D,H) embryos were analyzed by TUNEL to detect apoptotic cells and stained with antibodies against Pax2. In the mesenchyme surrounding anterior mesonephric tubules, levels of apoptosis are significantly elevated in Odd1 mutant (B, asterisk) compared with control embryos (A). By contrast, levels of apoptosis in E9.5 metanephric mesenchyme precursor cells are low in both Odd1 mutants (D) and controls (C). At this stage and axial level, Pax2 (D) and Eya1 (F) expression in prospective metanephric mesenchyme are absent in mutant embryos, while dermamyotomal Eya1 expression is normal (E,F). By E10.5, Odd1 null mutants (H) have increased levels of apoptosis in the metanephric mesenchyme (asterisk) compared with heterozygotes (G). At E10.5, Wt1 is expressed in the mesenchyme of both mutant (J, arrowhead) and wild-type (I) embryos. Similarly, Odd1 mutant embryos (L) exhibit substantial levels of Odd1 promoter activity, as detected by lacZ expression driven by the Odd1 promoter (heterozygote shown in K). a, aorta; d, duct; m, nephric mesenchyme; mm, metanephric mesenchyme; t, tubule; u, ureter.