Proplatelet formation deficit and megakaryocyte death contribute to thrombocytopenia in Myh9 knockout mice
Related Experiment Video
Updated: Jun 10, 2026
Proplatelet Formation Dynamics of Mouse Fresh Bone Marrow Explants
Published on: May 20, 2021
A Eckly1, J-Y Rinckel, P Laeuffer
1UMR_S949 INSERM-Université de Strasbourg, Etablissement Français du Sang-Alsace, Strasbourg, France.
Background:
Inactivation of the mouse Myh9 gene (Myh9Δ) or its mutation in MYH9-related diseases leads to macrothrombocytopenia. Paradoxically, previous studies using in vitro differentiated megakaryocytes showed an increased capacity for proplatelet formation when myosin was absent or inhibited.
Methods:
To explore the origin of the thrombocytopenia induced by myosin deficiency, we studied proplatelet formation using bone marrow explants of wild-type (WT) and Myh9Δ mouse where megakaryocytes have matured in their native environment.
Results And Discussion:
A dramatic decrease in the number and complexity of proplatelets was observed in megakaryocytes from Myh9Δ mice, while inhibition of myosin activity by blebbistatin increased proplatelet formation from WT mature megakaryocytes. Moreover, Myh9Δ megakaryocytes had a smaller size than the WT cells. These data indicate that myosin deficiency acts negatively on proplatelet formation, probably by impairing in situ megakaryocyte maturation, while myosin activity is dispensable at the latest stage of proplatelet formation. In addition, ultrastructural examination of Myh9Δ bone marrow revealed an increased proportion of megakaryocytes exhibiting signs of non-apoptotic cell death as compared with the WT mice.
Conclusion:
These data indicate that thrombocytopenia in Myh9Δ mice results from defective development of megakaryocyte size, impaired proplatelet formation and increased cell death.
Insights
Myosin II deficiency in mice impairs megakaryocyte development and proplatelet formation, leading to thrombocytopenia. This contrasts with in vitro findings, highlighting the importance of the native bone marrow environment for platelet production.
Area of Science:
- Hematology
- Cell Biology
- Molecular Biology
Background:
- MYH9 gene mutations cause macrothrombocytopenia in humans.
- Myosin II absence or inhibition paradoxically increased proplatelet formation in prior in vitro studies.
Purpose of the Study:
- Investigate the role of myosin II in megakaryocyte proplatelet formation within the native bone marrow environment.
- Determine the mechanisms underlying thrombocytopenia in Myh9-deficient mice.
Main Methods:
- Studied proplatelet formation in bone marrow explants from wild-type and Myh9-deficient (Myh9Δ) mice.
- Utilized ultrastructural examination to assess megakaryocyte cell death.
Main Results:
- Myh9Δ megakaryocytes showed significantly reduced proplatelet formation and smaller cell size compared to wild-type.
- Myosin inhibition in wild-type megakaryocytes increased proplatelet formation, suggesting myosin activity is dispensable for late-stage formation.
- Myh9Δ bone marrow exhibited increased megakaryocyte non-apoptotic cell death.
Conclusions:
- Myosin II deficiency impairs megakaryocyte maturation and proplatelet formation in vivo.
- Thrombocytopenia in Myh9Δ mice results from defective megakaryocyte development, impaired platelet production, and increased cell death.
