Fig. 2. Labeling and counting of human embryonic stem cell (hESC)-derived cardiomyocytes using lentiviral vector. (A ) Schematic representation of lentiviral vectors, pHR(+)c.MLC-2v.EGFP.R(−)W(+) and pHR(+)c.Ub.EGFP.R(−)W(+) used for identifying cardiomyocytes and determining transduction efficiency, respectively. (B ) To determine the total cell number in beating clusters, after dissociation cells were loaded with tetramethylrhodamine ethyl ester (TMRE; red) to visualize cell bodies. Myosin light chain-2v (MLC-2v)-enhanced green fluorescent protein (EGFP)-positive cells were counted by detecting green fluorescence, giving the number of ventricular myocytes. (C ) Summarized data from five separate differentiation experiments show high percentage of hESC-derived cardiomyocytes. Ub = ubiquitin.