Fig. 1. Phenotype of the 129Ola/C57BL6 raf-1–/– embryos. (A) raf-1–/– embryo at E9.5; (B) raf-1+/+ littermate embryo at E9.5; (C) raf-1–/– embryo at E9.5 in yolk sac; (D) raf-1+/+ littermate embryo at E9.5 in yolk sac; (E) PECAM-1 immunostaining of yolk sacs from wild-type embryo at E9.5 (left) and from mutant embryo (right). (F–I) PECAM-1 staining of raf-1+/+ embryo (F and H) and raf-1–/– embryo (G and I) at E9.5. (H) and (I) are magnifications of the embryonic brain regions. (J–O) Longitudinal sections through forebrain of raf-1+/+ (J, L and N) and raf-1–/– (K, M and O) embryos at E9.5. (J) and (K) were stained with haematoxylin and eosin, (L) and (M) were immunostained with a Ki67 antibody, and (N) and (O) were processed for TUNEL staining. Scale bars: A–E, 250 µm; F and G, 100 µm; H and I, 25 µm, J–M, 50 µm; N and O, 100 µm. NE, neural ectoderm; SE, surface ectoderm; Lu, lumen of prospective forebrain; MT, cephalic mesenchyme tissue.