Effect of p19^INK4D knockdown on cell cycle and CD41 or CD42 expression. CD34⁺ cells were transduced at days 1 and 2 (A-C) or days 5 and 6 (D,E) of culture with a control lentivirus and the lentivirus encoding either shRNA p19 (I) or shRNA p19 (II). GFP⁺ cells were analyzed at day 9. (A) Immunoblot analysis showing that phosphorylation of Rb on Serine 780 (p-Rb) was increased after MK transduction by the 2 shRNA p19. (B,D) Only the CD41⁺⁺CD42⁺⁺ cell population (left panel), corresponding to mature MKs, was analyzed for ploidy level by Hoechst staining (right panel). The mean ploidy (N) was calculated from the number of cells at each ploidy level. (C,E) The mean fluorescence intensity (MFI) of CD41 (left panel) and of CD42 (right panel) was analyzed separately for each ploidy class (from 2N to 16N). Panels B-E illustrate 1 representative analysis of 3 repeated experiments with similar results, and P values refer to 3 independent experiments.