Measurement of megakaryocyte frequency and ploidy distribution in unfractionated murine bone marrow

Measurement of megakaryocyte frequency, ploidy distribution, and maturation stage have been complicated by the low frequency of megakaryocytes in either bone marrow or spleen. Due to harsh labeling conditions, previous studies utilizing flow cytometry have not quantified cell recovery or megakaryocyte frequency. We have modified our two-color fluorescence-activated cytometric technique in order to identify megakaryocytes in unfractionated murine bone marrow with a fluoresceinated cell surface immunologic probe (heterologous polyclonal platelet antiserum) and to selectively measure megakaryocyte DNA content with propidium iodide using isosmolar conditions. Under these conditions, total nucleated cell recovery from unfractionated normal murine bone marrow, after all preparative procedures, averaged 68.0% +/- 5.0% (SD) with 93.5% +/- 2.0% DNA staining efficiency. Mean megakaryocyte frequency (n = 30) was 0.14% +/- 0.04%. Using both our previously described gating technique with single parameter analysis and our modified dual parameter technique, the modal megakaryocyte ploidy class was 16N. Low ploidy megakaryocytes, 2N and 4N, constituted 9.8% and 10.8%, respectively, of the total megakaryocyte population. Analysis of the megakaryocyte population with respect to cell surface fluorescence intensity demonstrated that the dimly fluorescent population contained an increased proportion of lower ploidy class cells (2N + 4N + 8N) compared with brightly fluorescent cells, which contained an increased proportion of higher ploidy cells (16N + 32N). Our modifications of the two-color technique yielded improved recovery of total nucleated bone marrow cells from unfractionated bone marrow and provided more precise measurements of megakaryocyte frequency and ploidy than previously available.