Fig. 10. Loss of high-level Bmp signaling after early Gdf7-mediated ablation. In situ hybridization on E10.5 and E12.5 ACTBCre;Gdf7DTA coronal cryosections. Semi-serial sections in G-L are 60-120 µm apart. (A-F) Bmp studies. Gdf7 is no longer detected in mutants (A), consistent with ablation. In controls, Bmp4 (D) and Bmp6 levels (F) are higher in the bilateral tCPe anlagen (arrowheads) and lower at the midline (arrows). After ablation, Bmp4 and Bmp6 levels are reduced and confined to a small midline domain (C,E). Epidermal/mesenchymal Bmp4 expression is maintained after ablation (C). (G-N) Msx1 studies. Msx1 is expressed in the tCPe anlagen at E10.5 (L) and in the definitive tCPe at E12.5 (N). After ablation, Msx1 expression in the neuroepithelium is dramatically reduced at E10.5 (G,I,K) and E12.5 (M). In situ hybridization of sections adjacent to those in A and M demonstrate well-preserved mRNA. Broken lines outline the neuroepithelium; arrows indicate the midline; arrowheads indicate tCPe or its anlagen. Scale bars: 0.1 mm.