Effect of rapamycin on murine MK differentiation, apoptosis, and ploidization. Murine Lin^– cells isolated from wild-type (wt), CdknIa (p21)^–/– and CdknIb (p27)^–/– mice were cultured in the presence of TPO without Rapa (TPO) or with Rapa (100 nM) added at day 0 and day 3 (TPO + Rapa). Analyses were performed at day 4. (A) Flow cytometry analysis showing the percentage of mature MKs expressing CD41 and CD42 (left panel) and apoptotic cells positive for Annexin V and 7AAD (right panel). (B) DNA content in mature MKs stained with propidium iodide (PI) and analyzed by flow cytometry. The mean ploidy was calculated from the number of cells in each ploidy level. 2N and 4N cells were not considered since they could represent cells other than MK. One representative experiment is shown from 4 performed with wt and 3 performed with CdknIa (p21)^–/– and CdknIb (p27)^–/– mice.