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Structure and Function of Platelets

The cell fragments known as platelets are disc-shaped, with an average diameter of about 3 μm and a thickness of roughly 1 μm. They play a crucial role in the body's vascular clotting system, which also involves plasma proteins, blood cells, and blood vessel tissues.
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Related Experiment Video

Updated: May 20, 2026

Proplatelet Formation Dynamics of Mouse Fresh Bone Marrow Explants
05:58

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Published on: May 20, 2021

Munc18b/STXBP2 is required for platelet secretion.

Rania Al Hawas1, Qiansheng Ren, Shaojing Ye

  • 1Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, KY 40536, USA.

Blood
|July 14, 2012
PubMed
Summary
This summary is machine-generated.

Munc18b is crucial for platelet secretion and exocytosis, as defects in this protein cause Familial Hemophagocytic Lymphohistiocytosis type 5 (FHL5). This study highlights Munc18b

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Last Updated: May 20, 2026

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11:42

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Published on: July 10, 2017

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Analyzing Platelet Subpopulations by Multi-color Flow Cytometry

Published on: June 10, 2025

Area of Science:

  • Hematology
  • Cell Biology
  • Molecular Biology

Background:

  • Platelet exocytosis is essential for hemostasis, releasing granule contents upon vascular damage.
  • Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and their regulators, like Sec/Munc18 proteins, mediate platelet exocytosis.
  • Platelets express three Munc18 isoforms: Munc18a, Munc18b, and Munc18c.

Purpose of the Study:

  • To investigate the role of Munc18b in platelet secretion and exocytosis.
  • To examine the impact of Munc18b deficiency on platelet function in Familial Hemophagocytic Lymphohistiocytosis type 5 (FHL5) patients.

Main Methods:

  • Analysis of platelet secretion in FHL5 patients with varying Munc18b gene defects (biallelic and heterozygous).
  • Quantification of Munc18b and syntaxin levels in patient platelets.
  • Co-immunoprecipitation assays to identify Munc18b interacting partners in human platelets.

Main Results:

  • Munc18b is identified as the major Munc18 isoform in platelets and is essential for platelet secretion.
  • FHL5 patients with biallelic Munc18b defects exhibit profoundly defective serotonin, ADP/ATP, and platelet factor 4 release, with lysosomal content release also affected.
  • Platelets from biallelic FHL5 patients show reduced Munc18b and syntaxin-11 levels, while Munc18b forms complexes with syntaxin-11, SNAP-23, and VAMP-8.

Conclusions:

  • Munc18b plays a critical role in platelet exocytosis, potentially acting as a limiting factor.
  • Munc18b appears to regulate syntaxin-11 function in platelet secretion.
  • Defects in Munc18b/STXBP2 are directly linked to defective platelet secretion observed in FHL5.