Fig. 5.

Sox1 onset in the embryonic axis is regulated by Fgf/retinoid signalling. (A) Sox1 mRNA is first detected in head-fold-stage chick embryos (HH stage 6) and appears progressively in a rostral to caudal direction, but is absent from the stem zone/caudal lateral epiblast (CLE). (B) Control DMSO or retinoic acid (RA) beads were grafted as indicated. All embryos were subject to in situ hybridisation for Sox1 except where stated otherwise. (C) Sox1 expression in normal quail (NQ) embryos and its reduction in vitamin A deficient (VAD) quails. (D) Sox3 expression in normal quails and its reduction in VAD embryos. (E) Beads soaked in DMSO (control) or the Fgfr inhibitor PD173074 were grafted as indicated. Sox1 expression is extended caudally in embryos grafted with PD173074-soaked beads. (F) Control (PBS), Fgf8 or Fgf4 presenting beads were grafted as indicated. Sox1 expression is locally inhibited when beads soaked in Fgf8 or Fgf4 are grafted near the preneural tube.