Hh signaling components but not shh are expressed in adult caudal fin primordium. Expression of gfp in caudal fin primordium at 3 dpf (A, arrow) overlaps with smu (B, arrow) gli3 (C, arrow) and you expression (D arrow). E, No shh expression is detected in the fin fold mesenchyme (arrow) while a weak residual activity in notochord is detected (open arrowhead). Expression of gfp and shh overlap in the floor plate (compare A to E, arrowheads). F-G, Expression of gfp is lacking in the posterior pectoral fin (arrow, F) where shh is expressed (arrow in G). Tail regions of 72 hpf embryos are shown anterior to the left in A-E and isolated pectoral fin buds of 60 h embryos are shown distal to the top posterior to the left in F, G. Scale bar in F represents 100 μm (A-B), 80 μm (C-E) and 40 μm (F, G). H, I, microsurgical preparation of fin fold tissues from 3 dpf zebrafish larvae for RT PCR analysis. H, ACFP tissue was cut by scalpel as indicated by green rectangular area (ACFP). Dorsal fin fold tissue containing notochord and neural tube with floor plate was excised similarly (red rectangular area, DFF). I, ACFP tissue after excision. Right panels show bright field view, left panels are fluorescent views of caudal fin tissues. J, RT PCR analysis of gene expression in the ACFP and DFF tissue samples. Gfp and smu but not shh are expressed in the ACFP. K, Real time PCR analysis of hedgehog genes in the ACFP and DFF. No known hedgehog genes are expressed in the ACFP. Agarose gel electrophoresis of PCR products in 40 cycles is shown on the left. Ct values of real time PCR cycles are shown on the right. L, Expression of hedgehog genes in the caudal fin of zebrafish during development. Agarose gel electrophoresis of real time PCR after 40 cycles on whole caudal fin fold and caudal fin samples are shown. Abbreviations: A, ACFP, D, DFF, d, days post fertilization, gfpn and neg c: gfp negative controls, ND, no specific product detected.