Fig. 8. Grem1 is required for cell survival during both limb and kidney organogenesis. (A) TUNEL assay to reveal apoptotic cell death on histological sections. In the absence of Grem1, cells in core limb bud mesenchyme undergo massive cell death by E11.0. (B) lacZ transcripts are detected in E11.0 forelimb buds (whole mount) to follow the fate of cells normally expressing Grem1 in both heterozygous and homozygous mutant limb buds. Note that lacZ-expressing cells survive in Gre^ORF/ORF limb buds. White arrowheads indicate the anterior and posterior domain boundaries. Forelimb buds in A,B are shown with ventral towards the bottom and distal towards the right. (C) Massive abnormal cell death is detected by TUNEL assay in the metanephric mesenchyme (mm) of Grem1 mutant kidneys by E11.5. Note that both wild-type and Grem1 mutant mesonephric mesenchyme (ms) undergoes normal apoptosis at this stage. (D) Pax2 expression in the nephrogenic tissue of a wild-type and Gre^ORF/ORF embryo. The sections shown are adjacent to the ones shown in C. Pax2 expression fails to be upregulated in the metanephric mesenchyme of mutant kidneys, while expression in mesonephric mesenchyme (ms) is similar to Wt. (C,D) Ventral views, posterior towards the bottom.