Fig. 4

fgf3 and fgf4 are expressed in the dental epithelium and lhx6 and lhx7 in the dental mesenchyme, but we did not detect fgf8 or pax9 expression in zebrafish tooth germs. (A) fgf8 expression is detectable in pharyngeal pouches until at least 44 h (arrowhead), but we do not detect it in tooth germs at any stage examined (arrow). (B) fgf4 is expressed in the dental epithelium at 48 h (arrow), as well as in lateral pharyngeal endoderm (arrowhead). (C) Transverse section at 56 h shows fgf4 expression localized to a subset of the dental epithelium (arrow). (D) fgf3 is expressed in a very similar pattern to fgf4 in the dental epithelium (arrow) and in the pharyngeal pouches (arrowhead), but is not detectable in the dental epithelium until 52 h. (E) At 56 h, fgf3 is expressed in what appears to be an identical subset of the dental epithelium as fgf4 (arrow). (F) lhx6 expression is detectable in lateral pharyngeal mesenchyme (arrowhead) and dental mesenchyme (arrow) at 48 h. (G) This lateral (arrowhead) and dental mesenchyme (arrow) expression is maintained at 56 h. (H and I) In the region of tooth formation at 56 h, lhx7 expression is localized to the dental mesenchyme (arrows). (J) pax9 expression is visible laterally in the pharyngeal arches at 48 h (arrowhead) but not in the tooth-forming region (arrow). (K and L) At 56 h, pax9 continues to be visible in the non-dental pharyngeal epithelium (double-arrows) and in lateral pharyngeal mesenchyme (arrowheads), but pax9 expression is undetectable in the tooth germs (arrows). (A, B, D, F, H, and J) Dorsal views, anterior to the left. (C, E, G, I, K, and L) transverse sections as in Fig. 2I. Scale bars = 100 μM.