Fig. 6. fgf3 is required in endoderm for the formation of posterior arches. (A-H) Alcian Blue staining of 4-day-old embryos. Ventral views, anterior to the left. (A-F) Wild-type embryos were either left untreated (A), immersed in Su5402 (B,C) or injected with morpholinos as indicated in lower right corner (D-F). (B) Su5402 prevents head cartilage formation, except for some very reduced anterior elements (arrowhead in C). (D,E) Cartilage in fgf4 morphants appears normal but fgf3 morphants do not develop branchial cartilage (except the fifth one, arrowhead), and develop a hyoid cartilage with inverted AP polarity. (F) Localisation of fgf3 morpholinos to anterior mesendodermal tissues is sufficient to disrupt branchial cartilage formation. The arrow indicates the injected side of the embryo. (G,H) Wild-type cells expressing Tar* and fgf3 morpholinos were grafted to cas embryos as in Fig. 4. At 4 days, compared to control cas embryos (G), grafted embryos developed mandibular and hyoid arch cartilages but not branchial cartilages. (I-N) Dorsal and lateral views, anterior to the left. Embryos were either injected with fgf3 morpholino or left untreated. In fgf3 morphants, cranial neural crest of stream III downregulates dlx2 expression (I,J). However pharyngeal endoderm differentiates normally as revealed by the expression of foxA2 (K,L) and the staining of pharyngeal pouches with Zn5 antibody (M,N).

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