Low ploidy megakaryocytes in steady-state rat bone marrow.

The amount of DNA in individual megakaryocytes (MK) was measured by Feulgen photometry performed on smears of steady-state rat bone marrow. The MK were identified by acetylcholinesterase (ACHE) staining. The method described is particularly suitable in the study of immature MK, hitherto difficult to examine for DNA content. The main MK ploidies were 8N, 16N, and 32N, comprising 33.4% +/- 1.4%, 40.8% +/- 1.4%, and 17.9% +/- 1.3%, respectively, of the total MK numbers. Only 6.7% +/- 1.7% had less than octoploid DNA content. Very few cells were found belonging to the 64N class. Among the immature MK, a relatively large fraction was found between the ploidy levels, indicating a rapid turnover within these ploidy classes. The demonstration of ACHE activity even in MK with a diploid DNA content indicates that the flow from the committed progenitors to differentiated MK occurs at the 2N level.