Spatial profile of ankrd1a activation during regeneration of zebrafish heart

Abstract

Introduction: In contrast to humans, zebrafish have a remarkable ability to regenerate injured heart through a complex and highly orchestrated processinvolving all cardiac structures. The majorsource of new myocardial cells are resident cardiomyocytes, which dedifferentiate and reinitiate proliferation, invading the area of injury to replace the lost myocardium. The response of the myocardium and coronary vasculature is preceded by activation of epi- and endocardium, which form active scaffolds to guide regeneration. The aim of thisstudy wasto identify cardiac structuresin which ankrd1a gene is activated during zebrafish heart regeneration. Methods: We crossed several zebrafish reporter lines: TgBAC(ankrd1a:EGFP) (to identify cells expressing ankrd1a), Tg(myl7:nls-dsRedExpress) (for labeling cardiomyocyte nuclei) and Tg(kdrl:RAS-mCherry) (for labeling endocardial/endothelial cells). Zebrafish hearts were cryoinjured and left to regenerate for 3 and 7 days. Dedifferentiating cardiomyocytes and epicardial cells were immunostained with anti-MYH7 and anti-caveolin1 antibody, respectively. Cells labeled with transgenes and immunostaining were visualized on tissue cryosections by fluorescent microscopy. Results: Zebrafish ankrd1a was activated in the injury border zone cardiomyocytes, located between the injured and remote myocardium. Its expression preceded that of a dedifferentiation marker, MYH7. The TgBAC(ankrd1a:EGFP) transgene was not detected in epicardial or endocardial cells of regenerating zebrafish heart. Conclusion: Activation of ankrd1a during regeneration of zebrafish heart is restricted to borderzone cardiomyocytes, implicating this gene in dedifferentiation and proliferation of cardiomyocytes. The absence of ankrd1a expression in epicardium and endocardium indicatesthat this gene does not contribute to the regeneration process occuring in these layers of the heart.