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RhoA/Cdc42 signaling drives cytoplasmic maturation but not endomitosis in megakaryocytes

Tobias Heib1, Heike M Hermanns2, Georgi Manukjan1

  • 1Institute of Experimental Biomedicine, University Hospital, University of Würzburg, 97080 Würzburg, Germany; Rudolf Virchow Center, University of Würzburg, 97080 Würzburg, Germany.

Cell Reports
|May 12, 2021
PubMed

Insights

RhoA and Cdc42 signaling are essential for megakaryocyte maturation and platelet production, but not for polyploidization. This discovery highlights separate regulation of megakaryocyte endomitosis and cytoplasmic maturation.

Area of Science:

  • Hematology
  • Cell Biology
  • Molecular Biology

Background:

  • Megakaryocytes (MKs) are large, polyploid cells in the bone marrow responsible for producing blood platelets.
  • Previous research indicated balanced Rho GTPase signaling (RhoA and Cdc42) is crucial for MK localization.
  • The specific roles of RhoA/Cdc42 in MK polyploidization and maturation remained unclear.

Purpose of the Study:

  • To investigate the role of RhoA/Cdc42 signaling in megakaryocyte polyploidization and cytoplasmic maturation.
  • To determine the impact of RhoA/Cdc42 deficiency on proplatelet formation and platelet production.
  • To elucidate the molecular mechanisms underlying RhoA/Cdc42-mediated MK maturation.

Main Methods:

  • Utilized conditional RhoA/Cdc42 double-knockout (DKO) mice.
  • Analyzed MK polyploidization, cytoplasmic maturation, and proplatelet formation.
  • Assessed gene and protein expression levels of key regulatory molecules (MLC2, β1-tubulin, LIM kinase 1, cofilin-1) and signaling pathways (MKL1/SRF).

Main Results:

  • RhoA/Cdc42 signaling is dispensable for MK polyploidization but essential for cytoplasmic maturation.
  • Proplatelet formation was severely impaired in DKO mice, leading to macrothrombocytopenia.
  • Observed downregulation of MLC2 and β1-tubulin, and upregulation of LIM kinase 1 and cofilin-1, linked to impaired MKL1/SRF signaling.

Conclusions:

  • Megakaryocyte endomitosis and cytoplasmic maturation are distinct, separately regulated processes.
  • RhoA/Cdc42 signaling critically controls cytoplasmic MK maturation, impacting platelet production.
  • Findings provide new insights into the molecular regulation of platelet biogenesis.
Keywords:
Cdc42Rho GTPaseRhoAcytoskeletonendomitosismegakaryocyteplateletproplatelet formationtranscription

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