Figure 4. Adult zebrafish cardiomyocytes express active p38α MAPK which is switched off upon entry into mitosis. Cultured adult zebrafish cardiomyocytes were immunolabeled for α sarcomeric actin (yellow) (A), phospho- p38α MAPK (green) (B), BrdU (red) (C) and a merged image with α sarcomeric actin (yellow), phospho- p38α MAPK (green), BrdU (red) and DAPI (blue) (D), the white arrow indicates the BrdU-positive cardiomyocyte in (A-D). Cultured adult zebrafish cardiomyocytes were immunolabeled for α sarcomeric actin (yellow) (E), phospho- p38α MAPK (green) (F), phospho histone H3 (PHH3) (red) (G) and a merged image with α sarcomeric actin (yellow), phospho- p38α MAPK (green), BrdU (red) and DAPI (blue) (H), the white arrow indicates the PHH3-positive cardiomyocytes in (E-H). A 10dpa cmlc2a-GFP regenerating heart immunolabeled for GFP (green) (I), phospho- p38α MAPK (magenta)(J), and phospho histone H3 (PHH3) (red) (K) and a merged image with GFP (green), phospho- p38α MAPK (magenta), phospho histone H3 (PHH3) (red) and DAPI (blue) (L), the white arrow indicates the PHH3-positive cardiomyocytes in (I-L).