Expression of Pitx2 and Shh in Astyanax and zebrafish. (A-C) pitx2 is expressed broadly and uniformly in the Astyanax oral region at early stages, later becoming strongest in tooth germs (arrowheads). (D-F) Sagittal sections reveal epithelial pitx2 expression (arrowheads) that includes morphologically visible tooth germs (arrow indicates mineralized matrix) and the oral valve (ov). (G-I) Astyanax shh expression is initially broad, becoming discrete in tooth germs by 72 hpf (arrowheads). (J-L) Sagittal sections reveal shh expression (arrowheads) to be epithelial and more posteriorly (lingually) restricted than pitx2. (L) At 72 hpf, shh expression is discontinuous between tooth germ (arrow) and oral valve. Arrow indicates mineralized matrix. (M-O) pitx2 is broadly expressed in zebrafish oral epithelium. Sagittal (N) and transverse (O) sections indicate labially restricted expression (arrowhead). No discrete expression corresponding to tooth germs is seen at any stage. (P-R) shh is expressed in zebrafish oral epithelium (arrowheads), showing little overlap with pitx2 expression, to which it is lingual. Abbreviations as in Fig. 1. y, yolk. Scale bars: 100 μm.
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