Fig. 6. Abnormal forebrain morphogenesis in the absence of retinoids. Lateral (A,B) and frontal (C,D,E) views of normal (A,C) and severely affected VAD (B,D,E) whole-mount stage 20 embryos. VAD embryos develop a smaller and single telencephalic vesicle circled in (D,E), which can be located laterally (D) or centrally (E) instead of two telencephalic (t) vesicles (A,C). Note (B) the ectopic morphological borders within the diencephalon (black arrowheads) and pronounced constrictions (red arrows) between vesicles. (F,G) Frontal sections of normal (F) and VAD (G) quail embryos at the level of the telencephalon/nasal pit. Note the lack of a rostral midline (rm) and the presence of a thick neuroectoderm in the single anterior vesicle of VAD embryos (arrow in G). e, eye; n, nasal pit; ov, optic vesicle; h, heart. Scale bars: 200 µm (bar in D also applies to E).