Fig. 1. Sox9 is expressed in prospective neural crest cells. Expression of the indicated genes in sections of the posterior and anterior open neural plate (PNP and ANP, respectively), and neural tube of HH stage 10 and stage 12 chick embryos. In posterior neural plate (B), Sox9 expression is restricted to the dorsal tips of the neural fold region, overlapping with FoxD3 (E), and precedes expression of Sox8 (A), Sox10 (C) and Slug (D). Anterior to this, expression of Sox10 (H) and Slug (I) are also found in a similar domain to Sox9 (G) and FoxD3 (J), but Sox8 (F) is still not detected in this domain. After neural tube closure, Sox8 (K), Sox9 (L), Sox10 (M), Slug (N) and FoxD3 (O) are expressed in the dorsal midline, where premigratory neural crest is located. Stage 10 images are adjacent sections from the open neural plate region of a HH stage 10 embryo. Stage 12 sections are from the prospective forelimb level of HH stage 12 embryos. (P) Schematic diagram of HH stage 10 chick embryo showing anterior and posterior levels of sections for the images in Q-T. (Q-T) Confocal images of Sox9 expression in HH stage 10 chick embryo from posterior to anterior levels. (Q) Sox9 is not detected in the most posterior regions. Anterior to this, Sox9 is upregulated in the dorsal tips of the closing neural folds (R,S). Sox9 expression is detected in the premigratory crest region at the more anterior region of closed neural tube (T). Expression of Sox9 is also seen at high level in the notochord (R-T).