Fig. 6

Histology analysis confirms the accuracy of echocardiography assessment for scar-free perfect regeneration of injured X. tropicalis hearts. A1: Representative H&E staining of the same-age nonapical resection group. A2: 3.3 × of dotted rectangle area. A3: 2 × of dotted rectangle area. B1: Representative H&E staining of the regenerated heart at 45 daar; echocardiography assessment identified regeneration in a scar-free perfect manner. B2: 3.3 × of dotted rectangle area. B3: 2 × of dotted rectangle area. C1: Representative Masson’s trichrome staining of the same-age nonapical resection group. C2: 3.3 × of dotted rectangle area. C3: 2 × of dotted rectangle area. D1: Representative Masson’s trichrome staining of a regenerated heart at 45 daar; echocardiography assessment identified regeneration in a scar-free perfect manner. D2: 3.3 × of dotted rectangle area. D3: 2 × of dotted rectangle area. The H&E staining showed that all the amputated areas were replaced by newly regenerated mature cardiomyocytes, as indicated by the regular striations, which were identical to normal control hearts. In addition, the epicardium had regenerated on the outer surface. Furthermore, Masson’s trichrome staining revealed that fibrotic structures were rarely observed in the fully regenerated myocardium and the epicardium, which had regenerated on the outer surface