Expression of hedgehog signal-related genes in regenerating tail. (A) Semi-quantitative gene expression analysis by reverse transcription–polymerase chain reaction (RT–PCR) was carried out. RNA was isolated from amputated tails at the indicated day. Specific primer pairs and PCR conditions are indicated in Additional file 2: Table S1. (B-E) Whole mount (B, D, E) and section (C) in situ hybridization of regenerated tail. The spatial expression of shh (B, C) ptc-1 (D) and ptc-2 (E) was analyzed on the regenerating tail at day 4 (C-E) or day 5 (B). Arrows indicate hybridization signal in the regenerating notochord (B, C) or spinal cord (D, E). A pair of arrowheads marks the amputation plane. Black dashed lines indicate the shapes of the regenerating spinal cord (C) or notochord (D, E). Bars, 100 μm.