title: No Evidence for Cardiomyocyte Number Expansion in Preadolescent Mice.
abstract: The magnitude of cardiomyocyte generation in the adult heart has been heavily debated. A recent report suggests that during mouse preadolescence, cardiomyocyte proliferation leads to a 40% increase in the number of cardiomyocytes. Such an expansion would change our understanding of heart growth and have far-reaching implications for cardiac regeneration. Here, using design-based stereology, we found that cardiomyocyte proliferation accounted for 30% of postnatal DNA synthesis; however, we were unable to detect any changes in cardiomyocyte number after postnatal day 11. (15)N-thymidine and BrdU analyses provided no evidence for a proliferative peak in preadolescent mice. By contrast, cardiomyocyte multinucleation comprises 57% of postnatal DNA synthesis, followed by cardiomyocyte nuclear polyploidisation, contributing with 13% to DNA synthesis within the second and third postnatal weeks. We conclude that the majority of cardiomyocytes is set within the first postnatal week and that this event is followed by two waves of non-replicative DNA synthesis. This Matters Arising paper is in response to Naqvi et al. (2014), published in Cell. See also the associated Correspondence by Soonpaa et al. (2015), and the response by Naqvi et al. (2015), published in this issue.
authors.affiliation: Cell and Molecular Biology, Karolinska Institutet, SE-17177 Stockholm, Sweden; Department of Forensic Medicine, The National Board of Forensic Medicine, SE-17177 Stockholm, Sweden.
authors.forename: Kanar
authors.initials: K
authors.lastname: Alkass
authors.affiliation: Cell and Molecular Biology, Karolinska Institutet, SE-17177 Stockholm, Sweden.
authors.forename: Joni
authors.initials: J
authors.lastname: Panula
authors.affiliation: Department of Medicine, Karolinska Institutet, SE-14186 Huddinge, Sweden.
authors.forename: Mattias
authors.initials: M
authors.lastname: Westman
authors.affiliation: Institut Curie, Centre de Recherche, F-91405 Orsay, France; INSERM, U1196; CNRS, UMR9187, F-91405 Orsay, France.
authors.forename: Ting-Di
authors.initials: TD
authors.lastname: Wu
authors.affiliation: Institut Curie, Centre de Recherche, F-91405 Orsay, France; INSERM, U1196; CNRS, UMR9187, F-91405 Orsay, France.
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Guerquin-Kern
authors.affiliation: Cell and Molecular Biology, Karolinska Institutet, SE-17177 Stockholm, Sweden. Electronic address: olaf.bergmann@ki.se.
authors.forename: Olaf
authors.initials: O
authors.lastname: Bergmann
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D049109:Cell Proliferation; D006321:Heart / Q000254:growth & development*; D008297:Male; D032383:Myocytes, Cardiac / Q000166:cytology*