Overexpression of p21 in human megakaryocytes.

(A) Sorting of infected CD41⁺ cells. Cells were infected at days 5 and 6 of culture and stained at day 7 with a PE–anti-CD41 mAb. Cells expressing high levels of EGFP and CD41, corresponding to infected megakaryocytes, were sorted in the R1 gate. (B) Effects of the p21 overexpression on the ploidy of human megakaryocytes. Cells infected with the VSV-G Migr retrovirus containing EGFP alone (panel Bi) or HA-tagged p21 and EGFP (panel Bii) were sorted as in panel A. Ploidy was then analyzed after PI staining. A typical experiment is illustrated. In this experiment, the ploidy level in the control was higher than in the experiment illustrated in Figure 1A. This difference was related to the variability observed among human samples. In 3 experiments, p21 overexpression markedly decreased (about 2-fold) the mean ploidy of human megakaryocytes.