Although mammalian hearts show almost no ability to regenerate, there is a growing initiative to determine whether existing cardiomyocytes or progenitor cells can be coaxed into eliciting a regenerative response. In contrast to mammals, several non-mammalian vertebrate species are able to regenerate their hearts1,2,3, including the zebrafish4,5, which can fully regenerate its heart after amputation of up to 20% of the ventricle. To address directly the source of newly formed cardiomyocytes during zebrafish heart regeneration, we first established a genetic strategy to trace the lineage of cardiomyocytes in the adult fish, on the basis of the Cre/lox system widely used in the mouse6. Here we use this system to show that regenerated heart muscle cells are derived from the proliferation of differentiated cardiomyocytes. Furthermore, we show that proliferating cardiomyocytes undergo limited dedifferentiation characterized by the disassembly of their sarcomeric structure, detachment from one another and the expression of regulators of cell-cycle progression. Specifically, we show that the gene product of polo-like kinase 1 (plk1) is an essential component of cardiomyocyte proliferation during heart regeneration. Our data provide the first direct evidence for the source of proliferating cardiomyocytes during zebrafish heart regeneration and indicate that stem or progenitor cells are not significantly involved in this process.
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We thank M. C. Fabregat, C. Rodriguez Esteban and I. Dubova for technical assistance, and A. Faucherre for constructive criticism of the manuscript. E.S. was the recipient of a pre-doctoral fellowship from the Ministry of Innovation, Universities and Enterprise (DIUE), Generalitat de Catalunya. This work was supported by grants from Fundacion Cellex, the Ipsen Foundation, the G. Harold and Leila Y. Mathers Charitable Foundation, Sanofi-Aventis, the Ministry of Science and Innovation (MICINN), CIBER, and the National Institutes of Health.
Author Contributions C.J., A.R. and J.C.I.B. conceived the project and designed the experiments. C.J. performed the molecular biology and established the transgenic lines. C.J., E.S. and M.R. conducted the experiments. M.M. performed the immunohistochemistry and confocal/transmission electron microscopy imaging. C.J., A.R. and J.C.I.B. wrote the manuscript.
This file contains Supplementary Figures 1-15 with legends.