Fig. 5. The puromycin-selected population expresses endothelial markers. (A) Puromycin-selected cells were cultured as spheroids in the presence of 10 ng/ml VEGF and stained for endothelial cell markers, CD31, VEGFR-2, CD34 and VE-cadherin. Note that all EGFP⁺ cells expressed VE-cadherin, CD31, VEGFR-2 and CD34. Note the presence of cell clusters that were negative for EGFP, but positive for CD31, VEGFR-2 and CD34. These clusters are likely to be endothelial progenitors. Bar, 50 µM. (B) Semi-quantitative RT-PCR analysis of undifferentiated B9TP (lane 1) and purified cells (lane 2) for the expression of the vegfr-2, vegfr-1, tie-1, icam-2 and hprt genes.