FIGURE 2

Myocardial tbx20 overexpression in adult hearts promotes CM proliferation and reduces fibrotic scars. (A) Schematic diagram of transgenes of the control line Tg(TRE3G:tbx20) and the inducible myocardial tbx20 overexpression line Tg(TRE3G:tbx20^CMOE) with DOX treatment. (B) Experimental strategy employed to induce myocardial tbx20 overexpression during heart regeneration. (C) Representative images of ISH with tbx20-E2A-mCherry probe on 7 dpa heart sections from DOX treated Tg(TRE3G:tbx20) and Tg(TRE3G:tbx20^CMOE) fish. Scale bar: 100 μm. (D) Upper panels: Representative confocal fluorescence images of heart sections from 7 dpa zebrafish immunostained for PCNA (green) and Mef2 (red). Insets showing high-magnification images of proliferating cardiomyocytes, arrowheads indicate PCNA⁺Mef2⁺ cells. Lower panels: Representative images of heart sections from 21 dpa fish stained with AFOG, muscle stained brown, collagen is blue and fibrin is red. The genotypes of fish were indicated above the images. Scale bar: 100 μm. (E) Quantification of CM proliferation at border zone and injury site on 7 dpa heart sections (n = 7 in each group). (F) Quantification of scar area at 21 dpa (n = 9 in each group). The fish in (C–F) were treated with DOX as indicated in (B). Each value in (E,F) represents mean ± SEM, **p < 0.01, ***p < 0.001.