Fig. 1. Expression of Alk2 and its putative ligands during cardiac development at E11.5. Radioactive in situ hybridization analysis of transverse sections through the cardiac OFT. Alk2 mRNA (A) displays a very similar expression pattern to Plxna2 (C) and Ednra (D), indicating expression by cardiac neural crest cells (Brown et al., 2001; Charite et al., 2001). Arrows indicate the positive hybridization signal (A,C,D). For comparison, cardiac neural crest cells were fate mapped using the WNT1-Cre/R26R reporter assay (Jiang et al., 2000) (B). An arrow indicates NCCs in the OFT region (blue signal). Bmp4 (F), Bmp5 (G), Bmp6 (H), Bmp7 (I) and Tgfb3 (K) are expressed in the myocardium, while Bmp2 (E) and Tgfb2 (J) are also expressed in the mesenchyme of OFT cushions. Scale bar: 200 µm.