Fig. 2. bapx1 is expressed at the developing jaw joint. (A-H) bapx1 expression in wholemount (A-D,G,H) and sectioned (E,F) wild-type embryos. (A) At 32 hpf, expression is seen in a cluster of first arch mesenchyme (arrow) as well as pharyngeal endoderm. (B) A higher magnification of A, showing that this domain appears to be at an intermediate dorsoventral position within the first arch. (C) Ventral view of 54 hpf embryo, showing bilateral first arch joint domains (arrows), first arch midline domain (white arrowhead), second arch midline domain (black arrowhead). (D) High magnification ventral-lateral oblique view of 54 hpf embryo showing the posterior end of the lower jaw (M) is surrounded by bapx-1-expressing cells, with apparent expression in cells in the posterior end of Meckel's cartilage (outlined with broken line). The jaw joint appears to be filled with and surrounded by bapx1-expressing cells. The second arch midline domain (arrowhead) and pharyngeal endoderm domains are also present. (E,F) Horizontal sections of bapx1 expression at 48 hpf showing (E) first arch jaw joint (arrow) and second arch midline domain (arrowhead), and (F) pharyngeal endoderm expression in pouches 2 through 6. (G,H) Two-colored in situ hybridization of expression of (G) dlx2 in red and bapx1 in blue at 32 hpf and (H) bapx1 in red and hand2 in blue at 30 hpf. bapx1 expression is ventral to a portion of dlx2 expression and dorsal to hand2 expression. The outline of the eye in the upper left, the first pharyngeal pouch in the upper-right corner, and the edge of the embryo towards the bottom are delineated. e, eye; M, Meckel's cartilage; p, pharynx; pe, pharyngeal endoderm; pp1, pharyngeal pouch 1; pp2, pharyngeal pouch 2; st, stomodeum. Scale bars: 50 µm.