Sections of zebrafish craniofacial cartilage reveal tissue specific gene expression of fzd7a, 7b, and 8a. (A) Schematic of a lateral view of a zebrafish at 55 h post-fertilization (hpf) highlighting the location of pharyngeal arches. Anterior is to the left. (B) Sagittal section at 55 hpf of Tg(fli1a:EGFP)y1/+ that expresses GFP within the neural crest tissue within the pharyngeal arches. Overlay of Nomarski image and fli1a:EGFP expression. (C) Schematic drawing of two pharyngeal arches at 55 hpf illustrating the different gene expression patterns of fzd7a, 7b and 8a. (D–F) Sagittal sections of the pharyngeal arches at 55 hpf. (D) fzd7a is expressed within the neural crest tissue of the pharyngeal arches. (E) fzd7b is expressed within the mesodermal core and the neural crest tissue. (F) fzd8a is expressed within the pharyngeal endoderm of the pharyngeal arches and is excluded from the neural crest and the mesodermal core. Note the similarity between the expression pattern of fzd7a at 55 hpf (D) and the flig1a:EGFP (B). (G–I) At 55 hpf fzd7b, but not fzd7a or 8a, are expressed within the symplectic cartilage elements (arrows). (J–L) At 3 days post-fertilization (dpf) fzd7a, 7b and 8a are no longer expressed within the craniofacial cartilage, but are expressed in the tissue surrounding the cartilage elements. (M) At 3 dpf it is clear that col2a1a is not expressed in the trabeculae but is expressed in the more posterior cartilage elements of the palaquadrate and Meckel’s cartilage. (N–O) Much like fzd7a, 7b and fzd8a, 2 (N) and fzd6 (O) are expressed in the tissue surrounding the cartilage elements and not directly in the cartilage at 3 dpf. Abbreviations: (e) eye, (mc) Meckel’s cartilage, (pq) palaquadrate, (t) trabeculae, (ep) ethmoid plate, (nc) neural crest, (pe) pharyngeal endoderm, (mes) mesodermal core, (ov) otic vesicle, and (p) pharyngeal arches. Bar equals 50 μm.