A, B. Whole mount staining of E8.75 using anti-cleaved caspase 3 antibody shows minimal overall apoptosis in FN-null embryos (B) compared with control embryos (A). Arrows point at apoptotic cells (dark brown spots). Older FN-null embryos show enrichment in apoptosis (reactivity with anti-cleaved caspase 3 antibody) in the neural tube segment located dorsal to the heart (C, D). E–L. Staining of transverse sections using the antibody to TFAP2α (red) to mark the NC and surface ectoderm (ec) in control, FN-null and integrin α5-null embryos. Apoptosis was detected using anti-cleaved caspase 3 antibody (green in E, I, G and K); Mitosis was detected using anti-pHH3 antibody (green in F, F′, F″, J, J′, H and L). Boxes in F and J are expanded in F′, F″, and J′, respectively. Neural and non-neural ectoderm are marked by dotted lines in F″, H, I, and L. Arrows point to examples of double-positive cells. Boxes in I and K show apoptotic CNC progenitors and CNCCs, respectively. Boxes in F′, F″ and H show mitotic CNC progenitors. Panel in J′ shows mitotic CNCCs. ec-surface ectoderm, g-gut, NT-neural tube, OFT-outflow tract. Scale bars are 100 μm.