Ectopic expression of wild-type Tbx20 rescues <i>whz</i> mutant embryos.

<p><b>(A, B)</b> Lateral view of <i>whz</i> mutant embryos control-injected with KCl <b>(A)</b> and wild-type zebrafish <i>tbx20</i> mRNA <b>(B)</b>, respectively. <b>(C)</b> Ectopic expression of wild-type zebrafish <i>tbx20</i> mRNA can rescue the heart phenotype of 73% of homozygous <i>whz</i> mutant embryos, whereas injection of KCl has no effect. <b>(D, E)</b> Dissected <i>whz</i> hearts injected with KCl <b>(D)</b> and wild-type <i>tbx20</i> mRNA <b>(E)</b> are stained against MEF-2 (red) after incorporation of 5-ethynyl-2'-deoxyuridine (EdU; green) to visualize cardiomyocyte proliferation. <b>(F)</b> <i>whz</i> mutant hearts injected with wild-type <i>tbx20</i> mRNA show significantly increased numbers of ventricular cardiomyocytes at 72 hpf <b>(E)</b> compared to control-injected <i>whz</i> mutants <b>(D)</b> (<i>whz+tbx20</i> mRNA: 142.5±10 SD, <i>whz</i> + KCl: 87.82±10 SD, n = 10; p = 0.0001). <b>(G)</b> Ventricular cardiomyocyte proliferation in <i>whz</i> mutant embryos injected with <i>tbx20</i> mRNA is significantly enhanced compared to control injected mutants at 72 hpf (<i>whz</i>+<i>tbx20</i> mRNA: 7±3% SD, <i>whz</i>+KCl: 1±2% SD, n = 10; p = 0.0001).