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Fig. 1. Heart regeneration and border zone cardiomyocyte proliferation is impaired in prrx1b−/− zebrafish. (A) AFOG staining on 30 dpi wild-type and prrx1b−/− heart sections showing fibrin in red, collagen in blue and remaining muscle tissue in orange. Scale bars: 100 μm. (B) Quantification of the remaining scar size at 30 dpi in prrx1b−/− hearts (n=6) and wild-type sibling hearts (n=9) (mean±s.d., P=0.0082, unpaired t-test). (C) AFOG staining on sections of 90 dpi hearts. Scars were completely resolved in wild-type hearts (n=12), whereas incomplete scar resolution was observed in prrx1b−/− four out of seven hearts. Scale bars: 100 μm. (D) Immunofluorescence staining on 7 dpi wild-type and prrx1b−/− heart sections using an anti-Mef2 antibody as a marker for cardiomyocyte nuclei, and an anti-PCNA antibody as a nuclear proliferation marker. Insets show higher magnifications of the boxed areas. Arrowheads indicate proliferating cardiomyocytes. Scale bars: 100 μm (main panels); 10 μm (insets). (E) Quantification of the percentage of proliferating (PCNA+) border zone cardiomyocytes in prrx1b−/− hearts (n=8) and wild-type sibling hearts (n=7) (mean±s.d., P<0.0001, unpaired t-test).