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Megakaryocytes increase in size within ploidy groups in response to the stimulus of thrombocytopenia
1Lawrence Berkeley Laboratory, University of California.
Abstract:
Experiments were done to determine if sizes of megakaryocytes within a defined maturation stage were strictly determined by amount of nuclear DNA. Normal mice, mice recovering from an acute episode of thrombocytopenia induced by a single injection of heterologous antiplatelet serum (APS), and mice with sustained thrombocytopenia from daily injections of APS were examined. Areas of mature megakaryocytes were measured in bone marrow smears stained with polychromatic stains. The nuclear DNA content of the same cells was then measured microspectrophotometrically after staining by the Feulgen reaction. Normal megakaryocytes showed a trimodal, lognormal distribution of nuclear chromophore, corresponding to 8n, 16n, and 32n with smaller numbers of 4n and 64n cells; 16n was the predominant ploidy class. In response to thrombocytopenia, ploidy values shifted: the proportions of 8n and 16n cells decreased; 32n and 64n cells increased; 128n megakaryocytes occasionally appeared. These shifts were accompanied by an increase in the average size of all megakaryocytes. In addition to shifts to higher ploidy values, megakaryocytes within ploidy groups became larger than normal megakaryocytes of the same ploidy especially in the mice with sustained thrombocytopenia. These findings show that megakaryocyte size in thrombocytopenic mice is influenced by factors other than the ploidy and maturity of the cell.
Insights
Megakaryocyte size is not solely determined by nuclear DNA content. Thrombocytopenia in mice leads to larger megakaryocytes, with size influenced by factors beyond ploidy and cell maturity.
Area of Science:
- Hematology
- Cell Biology
- Molecular Biology
Background:
- Megakaryocytes are essential for platelet production.
- Megakaryocyte size and ploidy are critical determinants of platelet output.
- The relationship between megakaryocyte size and nuclear DNA content under varying physiological conditions requires further investigation.
Purpose of the Study:
- To investigate whether megakaryocyte size is strictly determined by nuclear DNA content during maturation.
- To examine the impact of thrombocytopenia on megakaryocyte ploidy and size.
- To identify factors influencing megakaryocyte size beyond ploidy.
Main Methods:
- Bone marrow megakaryocytes from normal and thrombocytopenic mice were analyzed.
- Megakaryocyte area was measured using polychromatic stains.
- Nuclear DNA content was quantified via microspectrophotometry using the Feulgen reaction.
Main Results:
- Normal megakaryocytes exhibited a trimodal distribution of nuclear DNA content (ploidy), with 16n being predominant.
- Thrombocytopenia induced shifts towards higher ploidy values (32n, 64n, and occasional 128n).
- Megakaryocytes increased in average size during thrombocytopenia, with size increases also observed within specific ploidy groups.
Conclusions:
- Megakaryocyte size is not solely dictated by nuclear DNA content or maturation stage.
- Thrombocytopenia influences megakaryocyte size through mechanisms independent of ploidy.
- Additional factors beyond DNA content and maturity regulate megakaryocyte size in response to altered platelet counts.