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Fig. 4 Expression of Dlx2 orthologs in zebrafish, Synodontis and medaka. (A-C) dlx2b expression is absent at all stages from the zebrafish oral region, but present in forebrain (f). (D-F) dlx2a expression is absent from zebrafish oral epithelium at all stages, but present laterally in jaw mesenchyme (arrows) and forebrain. (G-L) dlx2a and dlx2b are expressed in tooth germs of Synodontis, while only dlx2a is expressed laterally in the jaw mesenchyme (arrows in J,K) and barbels (arrow in L). Both genes are expressed (arrowheads) in tooth germ epithelium (cytodifferentiation stage premaxillary germ in G; initiation stage dentary germ in J), and dlx2b was additionally detected in tooth germ mesenchyme (arrow in G). Arrowheads indicate one of three premaxillary germs per side in H, one of two dentary germs per side in K, and one of numerous germs visible in upper and lower jaws of I,L. (M-O) Medaka dlx2a is expressed in oral epithelium (arrowheads in M,N) and mesenchyme (arrows in M-O). Transverse section (M) indicates epithelium expression is in a medial band and sagittal sections (N,O) reveal that mesenchymal expression is lateral to this. Indicated stage is before visible signs of tooth initiation. All whole mounts in ventral view; transverse sections in B,E-G,J,M; sagittal sections in N,O. Abbreviations as in Fig. 1. f, forebrain; mx, maxillary process; y, yolk. Scale bars: 100 μm in A-H,J-K,M-O; 500 μm in I,L.