In vivo observations show that tadpole tail myofibres do not fragment. (a, b) Tail regeneration results of Car-nCre_Hsp-nlcCre_CALNL-GFP F1 transgenic tadpoles amputated approximately in the middle of the tail ("proximal amputations"). Many of the labelled myofibres next to the amputation plane were not found at 1 dpa probably because they degenerated. From 1 dpa till the end of the observations, the number and position of labelled myofibres did not change, indicating that there was no myofibre fragmentation. Also, no labelling was observed in the regenerate. n = 18 animals. (c, d) In vivo tracing of single myofibres in the distal part of the tail of Car-ERCreER/CALNL-GFP or Car-nCre_Hsp-nlcCre_CALNL-GFP transgenics. Myofibres close to the amputation plane generally showed a compact or retracted shape at 1 dpa (n = 94 fibres). During the next days, these muscle fibres started to recover the elongated shape, sometimes forming long citoplasmic projections (arrowheads). At 12 dpa, the shape of the myofibres was again elongated but generally different from the initial shape. Dashed lines: amputation planes.