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The early embryonic heart regenerates by compensation of proliferating residual cardiomyocytes after cryoinjury

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Abstract

The adult mammalian heart is non-regenerative because cardiomyocytes withdraw from the cell cycle shortly after birth. Embryonic mammalian hearts, in which cardiomyocytes are genetically ablated in a salt-and-pepper–like pattern, regenerate due to compensation by residual cardiomyocytes. To date, it remains unknown whether or how transmural ventricular defects at the looped heart stage regenerate after cryoinjury. We established a cryoablation model in stage 16 chick embryonic hearts. In hearts at 5 h post cryoinjury (hpc), cryoinjury-induced defects were approximately 200 µm in width in the primitive ventricle; thereafter, the defect was filled with mesenchymal cells accumulating between the epicardium and endocardium. The defect began to regress at 4 days post cryoinjury (dpc) and disappeared around 9 dpc. Immunohistochemistry showed that there were no isl1-positive cells in either the scar tissue or residual cardiomyocytes. BrdU incorporation into residual cardiomyocytes was transiently downregulated in association with upregulation of p27 (Kip1), suggesting that cell cycle arrest occurred at G1-to-S transition immediately after cryoinjury. Estimated cell cycle length was examined, and the results showed that the shortest cell cycle length was 18 h at stages 19–23; it increased with development due to elongation of the G2-M-G1 phase and 30 h at stages 27–29. The S phase length was constant at 6–8 h. The cell cycle length was elongated immediately after cryoinjury, and it reversed at 1–2 dpc. Cryoablated transmural defects in the early embryonic heart were restored by compensation by residual myocytes.

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Funding

Japan Society for the Promotion of Science (JSPS); Grant numbers: 25460273, 19K07251.

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Correspondence to Yuji Nakajima.

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Animal handling and procedures were approved by the Osaka City University Animal Care and Use Committee (approval reference number 18026), as specified in the NIH Guide for the Care and Use of Laboratory Animals (Eighth Edition).

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The authors declare that there is no conflict of interest.

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Narematsu, M., Nakajima, Y. The early embryonic heart regenerates by compensation of proliferating residual cardiomyocytes after cryoinjury. Cell Tissue Res 384, 757–769 (2021). https://doi.org/10.1007/s00441-021-03431-w

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  • DOI: https://doi.org/10.1007/s00441-021-03431-w

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