ES cell–derived megakaryocyte maturation.

Blast cell colony cells derived from mpl^−/− flmpl, mpl^−/− Δ3mpl, mpl^−/− Δ34mpl ES cells were plated in serum-free liquid medium in the presence of PEG-rhuMGDF and were cultured for 5 days. (A) Megakaryocyte displaying proplatelets (arrows) (magnification × 200). (B) Ploidy analysis of megakaryocytes. After labeling with anti-CD41 antibody to identify megakaryocytes, cells were labeled with propidium iodide to evaluate DNA content. DNA content was scored on CD41⁺ cells. Images were made with Adobe Photoshop 5.0. (C) Flow cytometry quantification of platelets, defined as CD41⁺ elements with the same scatter properties as murine blood platelets (dot plot). SSC indicates side scatter; FSC, forward scatter.