Isolation of mouse MK populations at successive stages of maturation. (A) Cells harvested on different days of fetal liver culture were labeled with CD41 antibody and sorted by flow cytometry, using gates suited to the forward-scatter (FSC; size) and CD41 expression level (fluorescence) of MKs. Parameters chosen for isolating MK-3, MK-P, MK-4, and MK6 are boxed within the corresponding plots. (B) May-Grünwald-Giemsa–stained cells representing the 4 MK populations sorted by flow cytometry. (C) Profiles of the DNA content of the sorted MK populations, labeled with propidium iodide and analyzed by flow cytometry.