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Updated: May 6, 2026
Megakaryocyte Differentiation and Platelet Formation from Human Cord Blood-derived CD34+ Cells
Published on: December 27, 2017
Multimerin is found in the alpha-granules of resting platelets and is synthesized by a megakaryocytic cell line
C P Hayward1, D F Bainton, J W Smith
1Department of Medicine, McMaster University Medical Centre, Hamilton, Canada.
Abstract:
In this report, we describe the intracellular localization of multimerin in platelets and its biosynthesis by Dami cells, a megakaryocytic cell line. Immunoelectron microscopy was used to examine frozen thin sections of resting and activated platelets. Multimerin was localized within the platelet alpha-granule in an eccentric position. Within activated platelets, multimerin was found in the surface-connected open cannalicular system and on the external plasma membrane. Light microscopic immunocytochemistry demonstrated multimerin in normal megakaryocytes and in Dami cells after stimulation with PMA. Confirmation of multimerin biosynthesis by Dami cells was obtained by metabolic labeling studies. Both platelet and Dami cell multimerin demonstrated several subunit sizes on reduced SDS-PAGE. However, peptide mapping confirmed structural homology between the different multimerin subunits. Glycosidase digestion demonstrated that multimerin is heavily glycosylated with mainly complex, N-linked carbohydrate. In contrast to the multimerin isolated from platelets, cultured Dami cells secreted mainly smaller multimers of the protein. Biosynthesis of multimerin by a megakaryocytic cell line supports endogenous biosynthesis by megakaryocytes as the origin of this platelet alpha-granule protein.
Insights
Multimerin, a platelet alpha-granule protein, is synthesized by megakaryocytes. This study localizes multimerin within platelet alpha-granules and confirms its biosynthesis by Dami cells, a megakaryocytic cell line.
Area of Science:
- Hematology
- Cell Biology
- Protein Biochemistry
Background:
- Multimerin is a protein found in platelet alpha-granules.
- Its cellular origin and precise localization within platelets have not been fully elucidated.
- Understanding multimerin's biosynthesis is crucial for platelet function research.
Purpose of the Study:
- To determine the intracellular localization of multimerin in platelets.
- To investigate the biosynthesis of multimerin by Dami cells, a megakaryocytic cell line.
- To confirm the origin of platelet multimerin.
Main Methods:
- Immunoelectron microscopy of resting and activated platelets.
- Light microscopic immunocytochemistry of megakaryocytes and Dami cells.
- Metabolic labeling studies and SDS-PAGE analysis of Dami cells.
- Peptide mapping and glycosidase digestion for protein characterization.
Main Results:
- Multimerin is localized eccentrically within platelet alpha-granules.
- Upon platelet activation, multimerin translocates to the open canalicular system and plasma membrane.
- Dami cells, stimulated with PMA, synthesize and secrete multimerin, exhibiting structural homology with platelet multimerin.
- Multimerin is heavily glycosylated with complex, N-linked carbohydrates.
Conclusions:
- Dami cells serve as a valid model for studying multimerin biosynthesis.
- The findings support endogenous biosynthesis by megakaryocytes as the source of platelet alpha-granule multimerin.
- This research clarifies the cellular origin and trafficking of multimerin in platelets.
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