Mice were labeled with EdU during indicated time frames. CyclinA2-EGFP-positive cells were extremely rare. A single CyclinA2-EGFP-positive cardiac myocyte in the field is shown (white circle). CyclinA2-EGFP-positive but EdU-negative cardiac myocytes were also observed. Scale bar: 50 μm. B, Fluorescence microscopy of heart sections from TnT-Cre;CyclinA2-LacZ-EGFP mice at PN14 stained for CyclinA2-EGFP, PDGFRα, CD31, CD45, CD146, EdU, and DAPI. All EdU-positive/ CyclinA2-EGFP-negative cells were labeled with either anti-PDGFRα, anti-CD31, anti-CD45, or anti-CD146 antibody (blue circles). Scale bar: 50 μm. C, Quantitative analysis of CyclinA2-EGFP myocardial cells throughout PN14 and PN15. Note gradual and steady decrease.