Nikaido et al., 2007 - Initial specification of the epibranchial placode in zebrafish embryos depends on the fibroblast growth factor signal. Developmental dynamics : an official publication of the American Association of Anatomists   236(2):564-571 Full text @ Dev. Dyn.

Fig. 1 Expression of zebrafish sox3 during development. A-C: Expression of sox3 and pax8 in the placodal region at the one-somite stage. sox3 is expressed both in the neural plate (np) and placode (arrowhead in A). Embryos were stained for sox3 (B, red), and the same embryos were further stained for pax8 (C, blue). Insets in B and C are high-magnification views of the regions enclosed by the white squares. Arrowheads in B and C mark the same cell. D-I,I′ Expression of sox3 in the epibranchial placodes during somitogenesis. sox3-expressing subdomains are indicated by arrowheads (D-G) or "p1"-"p4" (H). Sections I and I′ were taken at the planes shown in H. In I and I′, arrows indicate mesendodermal and ectodermal sox3 expression, respectively. D′-G′: Comparison of sox3 (red) and pax2a (blue) expression. Black arrowheads indicate sox3-expressing subdomains. J:ngn1 expression in a wild-type embryo at 26 hours postfertilization (hpf). K,L: Comparison of the expression of sox3 (red) and ngn1 (purple) in the same wild-type embryo at 26 hpf. Asterisks indicate the mesendodermal sox3 expression. A,H,J-L: Dorsal (A) or dorsolateral (H,J-L) views, with anterior to the left. B-G,D′-G′: Flat-mount dorsal views, with anterior to the left. In all panels, the stages examined are indicated at the bottom, and the genes examined are at the top right. f, facial placode/ganglion; g, glossopharyngeal placode/ganglion; o, otic vesicle; v, vagal placode/ganglion. Scale bars = 100 μm.

Fig. 2 Fibroblast growth factor-8 (FGF8) signal is required for development of the early placode. A: Expression of fgf8 in the anterior hindbrain region at the one-somite stage. B: Comparison of the expression of fgf8 (blue) and sox3 (red) at the one-somite stage. Arrowheads in A,B indicate the lateral border of the fgf8 domain in rhombomere 4 (r4). C,D: Transverse sections at the r4 level show intense expression of sox3 (C) and fgf8 (D) in the ectoderm at the one-somite stage. The edges of the neuroectoderm are marked by arrowheads. A few cells faintly expressing sox3 (C) or fgf8 (D) were observed in the mesendodermanl region (small arrows). E,F:sox3 expression in embryos obtained by intercross of ace heterozygous adults. Twenty-five percent of the obtained embryos (ace -/-) showed no placodal expression (E), while the others (75%, ace +/+ or ace +/-) showed normal sox3 expression (F). G,H:sox3 expression in the ace homozygous embryos implanted with FGF8b-soaked beads (G) and bovine serum albumin (BSA) -soaked beads (H). Arrowheads indicate the positions of the implanted beads. A,B,E-H: Dorsal views with anterior to the left. Genes examined are shown at the top right. e, ectoderm; y, yolk. Scale bars = 200 μm in A,B,E-H, 50 μm in C,D.

Fig. 3 Dependence of the development of the epibranchial placode on the fibroblast growth factor (FGF) signal. A,B: Zebrafish embryo treated with SU5402 (A) and dimethyl sulfoxide (DMSO, B) from 90% epiboly to 26 hours postfertilization (hpf). The disrupted isthmus is shown with a large arrowhead, and an arrow indicates the reduced otic vesicle. C,D:sox3 expression in the head of the one-somite stage embryos treated with SU5402 (C) or DMSO (D) from 90% epiboly stage to the one-somite stage. E-H:sox3 expression at the 10-somite stage (E,F) and phox2a expression at 48 hpf (G,H) were examined in embryos treated with SU5402 (E,G) or DMSO (F,H) from 90% epiboly to the one-somite stage. The small arrowhead indicates residual posterior sox3 expression at this stage. A,B: Lateral views, with anterior to the left and dorsal to the top. C-H: Dorsal views (C-F) or dorsolateral views (G,H), with anterior to the left. The stage of the SU5402 treatment is indicated at the bottom left in each panel. Genes and stages examined are shown at the top right in each panel. f, facial ganglion; g, glossopharyngeal ganglion; v1, v2, vagal ganglion. Scale bar = 200 μm.

Acknowledgments:
ZFIN wishes to thank the journal Developmental dynamics : an official publication of the American Association of Anatomists for permission to reproduce figures from this article. Please note that this material may be protected by copyright. Full text @ Dev. Dyn.