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Fig. 5 Effect of amputation level on shh expression. (A) Schematized representation of the levels of amputation with respect to the first bifurcation of the caudal fin rays. A “short cut” was done within 1-2 segments after the bifurcation. A “long cut” was made further than 2 segments distal to the bifurcation. The small insert shows the ray fusions induced by the short, but not by the long cut. (B) Representative fusions of caudal fin. Due to the uneven level of the first bifurcations across the fin, some rays underwent a “short cut” (s), whereas some underwent a “long cut” (l). Only rays with short cuts have fused branches. (C-E) Shh expression in “short cut” fin rays at 3 days (C), 4 days (D), and 5 days (E). The cells expressing shh form more diffuse patterns at 3 and 4 days compared to fins that had a long cut (see Fig. 2). The two groups of cells expressing shh, announcing a bifurcation, are clearly resolved at 5 days. The bracket in E indicates ray fusion. Arrows in C,D,E, indicate the level of amputation. Scale bars, 80 μm.