Recombinant thrombopoietin increases DNA content of PB-derived MKs but reduces DNA content of CB-derived MKs. PB- and CB-CD34⁺ cells cultured in UCM with 100 ng/mL rTpo or in CM without Tpo for 14 days were analyzed by flow cytometry and light microscopy. (A) Representative density plots and histograms from one experiment are displayed to show the ploidy distribution of PB- and CB-MKs. MKs were first selected by gating on CD41-FITC versus forward scatter. Propidium iodide versus CD41-FITC density plots and histograms were then generated to assess the ploidy distribution. The results were consistent in all 4 experiments performed. (B) Cytospin preparations of the cultured cells show that PB CD34⁺ cells generated large, multinucleated MKs in UCM cultures + 100 ng/mL rTpo and small immature MKs in CM without rTpo. In contrast, CB CD34⁺ cells generated large, multinucleated MKs in CM cultures without rTpo and immature MKs in UCM cultures + 100 ng/mL rTpo. Photomicrographs of Wright-Giemsa–stained cytospin preparations were taken on a Labophot-2 microscope using a 10× eyepiece and a 40×/0.65 objective lens (Nikon, Melville, NY). A SPOT-RT 2.2.0 color camera and SPOT Advanced 4.0.9 software (Diagnostic Instruments, Sterling Heights, MI) were used to capture and digitally acquire images, which were then inserted into PowerPoint 10 (Microsoft, Redmond, WA) for processing.