Fig. 1

Endoderm-specific expression of ihha in early zebrafish development up to 96 hpf. A, A¹, Expression of ihha is initiated in the endoderm at the level of 2–3 somites at 24 hpf. A¹, Dorsal view. B, Expression of ihha increased at 36 hpf; B¹, lateral view shows a prominent domain of ihha expression in the foregut. C, D, At 50 hpf ihha expression is strong in the esophagus, swimbladder, liver, pneumatic (arrowhead) and extrahepatic ducts (arrows), lateral view. Caudal to the extrahepatic duct expression is in the region giving rise to the primitive intestine; E, E¹, by 74 hpf, ihha expression continues to be strong along the gastrointestinal tract in the esophagus and intestine, and in the pneumatic duct and swimbladder, but declines in the liver at 96 hpf, F, A–F whole mount. G–I, Cross-sections at 74 hpf show expression of ihha in the epithelium of the esophagus, pneumatic duct, swimbladder and intestine. The level of sections in G–I is shown by white lines in E. J, Schematic representation of ihha expression in the esophagus, gut, pneumatic duct and swimbladder. Unless otherwise stated anterior is to the left for all whole mounts. Abbreviations: e, endoderm; es, esophagus; ehd, extrahepatic duct; g, gut; l, liver; pd, pneumatic duct; sb, swimbladder; s, somite; y, yolk; *, midline. Scale bars: 250 μm.