Fig. 1

Knocking out both TRα and TRβ (TRDKO) enable tail regeneration at metamorphic climax stage 61 in Xenopus tropicalis. A Morphological changes during tail regeneration show that tail is able to fully regenerate up to stage 60 but fails to complete the process at the climax stage 61 of metamorphosis in wild type tadpoles while TRDKO tadpoles retain ability to regenerate the tail completely even at stage 61. The white dash lines and white arrowheads indicate amputation site and regenerated portion of the tail, respectively. Right panels are regions in white dashed boxes in left panel at a higher magnification. Scale bar (shown only in Panel x): 1 mm. B Percent of animals have tail regeneration at indicated stages 7 days post-amputation. Note that 100% tadpoles of both wild type X. tropicalis and X. laevis, and TRDKO could regenerate the tail when amputated at all stages between 48 and 59, including stage 48–49, stage 51, stage 54, stage 56, stage 58 and stage 59. At stage 61, 100% of the TRDKO tadpoles could regenerate but none of wild type X. tropicalis and X. laevis animals had significant regenerated tail 7 days after amputation at stages 60–61. The data were shown as mean values of at least 3 replicates with SE. **P < 0.01, ns: no significant. C Quantitative analysis of the length of the regenerated tail reveals that both wild type and TRDKO can regenerate the tail at early metamorphic stage 56 while wild type tail fails to complete tail regeneration at stage 61, unlike the TRDKO tail at stage 61. The length of the regenerated portion of the tail was measured from at least 3 tadpoles at stage 56 or 61 and presented as mean ± SE, ns, no significant