Fig. 4

Bmi1-CPC response to acute injury in adult and neonatal mouse hearts. a Detailed transverse section of Bmi1-YFP left ventricle 3 months post-acute myocardial infarction (AMI). Scale bar = 200 μm. b YFP⁺ cardiomyocytes (CM) 3 months post-AMI, located near the injured area (left) and at sites distant from the infarcted zone (right); (n = 3). Dotted line delineates the border of the injured area. Arrows indicate YFP⁺ CM. Scale bars = 50 μm. c Adult CM freshly isolated 4 months post-AMI. YFP⁺ CM express cardiac proteins related to contractility and gap junctions, including sarcomeric α-actinin (SαA), (cardiac troponin T (cTnT), and connexin 43 (CX43). Scale bars = 50 μm. d Number of YFP⁺ CM in adult mice (4 months post-AMI, n = 4) compared with the number in non-infarcted hearts (homeostasis; 4 months post-AMI, n = 4). *P < 0.05. Data shown as mean ± SEM. CM were plated, fixed, and stained for SαA, GFP, and DAPI. The number of YFP⁺ CM was assessed in duplicated microscope cover glasses (12 mn diameter). At least 200 CM per cover glass were counted. e Nucleation of YFP⁺ CM in homeostasis and after AMI (n = 3-4 mice). Data shown as mean ± SEM. CM were isolated 4 months post-AMI, plated, fixed and stained for SαA, GFP and DAPI. Nucleation of YFP⁺ CM was assessed in duplicated microscope cover glass (12 mm diameter). At least 200 CM per cover glass were counted. f Schematic representation of apical resection experiments on tamoxifen (TM)-induced neonatal hearts. g YFP⁺ fraction in postnatal day 1 (P1) Bmi1-YFP hearts accounts for 0.3 ± 0.04 % of total mononuclear heart cells (n = 8). YFP⁺ cells were not detected in non-induced controls (Bmi1-YFP^NI, inset). Data shown as mean ± SEM. h Hematoxylin/eosin staining of mouse heart at 1, 7, and 21 days post-apical resection (dpr) in neonatal (P1) mouse pups. Dashed line delineates the resection plane. Enlarged view of resected areas is shown, delimited by dashed squares. Scale bars = 1000 μm. i Immunodetection of YFP⁺ clusters (arrows) near the injured area (left and center) and atrium (right) 21 days after neonatal heart apical resection (n = 3). Dashed line delimits the regenerated apex 21 dpr. Scale bars = 50 μm (left, right), and 20 μm (center)