Figure 2. Generation of MCF7 cells harboring the hTERT-eGFP reporter, to select a sub-population of cells with high telomerase activity.

Panel A. MCF7 cells were transduced with a lentiviral vector driving eGFP protein expression, under the control of a 1.5-kB fragment of the hTERT promoter. This DNA construct also contains a puromycin-resistance cassette for antibiotic-resistance selection. Panel B. After selection with puromycin, MCF7-hTERT-eGFP cells were subjected to FACS sorting to visualize the broad distribution of eGFP expression, which serves as a surrogate marker of telomerase activity. Panel C. Note that very few cells in MCF7-hTERT-eGFP monolayers showed high GFP fluorescence. Panel D. Note the dramatic enrichment of GFP(+) cells in MCF7 cell mammospheres (> 50 μm), each containing usually 1-to-2 GFP-high cells.