Hedgehog signaling is required for the patterning of the caudal fin. A-C: caudal fin primordium development is blocked in syu-/- and smu-/- mutants. A, Wild type embryo tail showing normal embryonic fin fold and melanophore streak (arrowhead) in bright field (left) and GFP fluorescence (right) marking the adult caudal fin primordium (arrow). B, C, In syu-/- and smu-/- mutants gfp expression in the fin fold is absent (arrows). The melanophores are abnormally arranged (arrowheads in left). Expression of GFP in the floor plate and residual activity in the notochord is present (arrowhead in B, right). D-I, Hedgehog signaling regulates gene expression in the caudal fin primoridum. Expression of bmp4 (arrows in D, E) and ptc (arrows in F, G) are lost or strongly reduced in smu-/-. In contrast, the mesenchyme marker msx-C is expressed in the embryonic fin fold in wild type (H, arrow) and in smu-/- mutants (I, arrow). Lateral views on embryonic tail region of 72 hpf embryos are shown. Scale bar in F indicates 100 μm.