Tadpole tail myofibres show a dedifferentiation phenotype. (a, b) Control tail myofibres, showing the orderly aligned sarcomeric structure in semithin sections (a) and TEM micrographs (b). (c-e) At 1 dpa, dead myofibres are frequently observed next to the amputation plane in the tail (asterisk). Many myofibres show a more compact shape with an apparently normal sarcomeric structure (arrows) while others show some sarcomeric disorganization (arrowhead in d). In few cases, the sarcomeric disorganization is more severe (arrowhead in e). (f-h) At 3 dpa, a considerable regenerate has formed (f) and more stump myofibres show the dedifferentiation phenotype (g, h). (g) Myofibre close to amputation plane with an irregular shape and big regions in the sarcoplasm devoid of sarcomeres (arrowhead). (h) Another myofibre, farther from the amputation plane, showing the same phenotype (arrowheads). Externally to this myofibre there is a longer fibre. These longer muscle fibres never show an obvious dedifferentiation phenotype. (i) Confocal image of a tail myofibre with disarranged alpha-sarcomeric actin (ASA, arrowhead) at 3 dpa. (j) TEM micrograph of a myofibre with dissociating myofibrils (arrowheads) next to a region with organized myofibrils (arrow), at 3 dpa. (k, l) Muscle in the zeugopod of stage 54 hindlimbs is very immature. It is mainly composed of myoblasts and young myofibres (arrows). (m, n) At 1 dpa, no obvious changes are observed (arrows: young myofibres). (o-r) At 3 dpa, distal myofibres are still very similar to the ones observed at 0 and 1 dpa (arrows: young myofibres). No obvious dedifferentiation was observed in the limb muscle. Dashed lines: amputation planes. n ≥ six sections per animal, three animals per time point.