Fig. 5. VAD embryos show increased cell death in ventral neuroectoderm and head mesenchyme. Apoptotic cells in sections of normal (A-E) and VAD (F-J) quail embryos detected using the TUNEL assay (A-C,F-H), and neural crest cells detected using an HNK1 antibody (D,E,I,J). (A,F,D,I) Mid-sagittal and para-sagittal sections, (B,G,E,J; insets in A,F) frontal and (C,H) horizontal sections. Stage 10 VAD embryos show an increased rate of apoptotic cells in ventral neuroectoderm (arrow in F and arrowheads in inset) and foregut endoderm (asterisk in F and arrow in inset), but no change in the distribution of neural crest cells (D,I). VAD embryos (arrow in I) have an apparent difference of HNK1-positive cells because the section is more lateral. (B,G) In stage 13/14 VAD embryos, ventral neuroectodermal (arrows in G) and mesenchymal cells around the eye regions (arrowheads in G) show a dramatic increase of programmed cell death. (C,H,E,J) At stage 19/20 the dramatic increase in the rate of dying cells is still detected in neuroectodermal (arrows in H) and head mesenchymal tissues (arrowheads in H). Moreover, the absence of HNK1-positive cells in ventral regions (arrow in J) indicates a lack of neural crest-derived cells. Lines in A and F designate the level of the frontal section showed in the insets. Scale bars: 100 µm in A,F,D,I; 200 µm in B,C,E,G,H,J.