Increased frequency of double-stained CD34⁺CD41⁺ cells in PD98059-treated cultures. Cells from cultures containing or not 6 μmol/L PD98059 were harvested at different time intervals and stained simultaneously with R-PE-anti-CD34 and FITC-anti-CD41 (or FITC-anti-CD34 and R-PE-anti-CD41) antibodies. (A) FACS dot plot from a representative experiment on day 7 cells. (B) Percent of CD34⁺ cells among the CD41⁺ cell population after 7 and 11 days of culture in the absence (−) or in the presence (+) of PD98059 in 5 independent experiments.