Platelet alpha-granule fibrinogen, albumin, and immunoglobulin G are not synthesized by rat and mouse megakaryocytes.

P Handagama; D A Rappolee; Z Werb; J Levin; D F Bainton

doi:10.1172/JCI114848

Department of Pathology, University of California, San Francisco 94143.

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Department of Pathology, University of California, San Francisco 94143.

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Department of Pathology, University of California, San Francisco 94143.

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Department of Pathology, University of California, San Francisco 94143.

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Department of Pathology, University of California, San Francisco 94143.

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Published in Volume 86, Issue 4 on October 1, 1990
J Clin Invest. 1990;86(4):1364–1368. https://doi.org/10.1172/JCI114848.
© 1990 The American Society for Clinical Investigation

Published October 1, 1990 - Version history

It has been assumed that endogenous synthesis by the platelet precursor cell, the bone marrow megakaryocyte, is the major source of platelet alpha-granule protein. To test this hypothesis, we used mRNA phenotyping to detect in megakaryocytes the presence of mRNA transcripts specific for various proteins. Our results indicate that megakaryocytes synthesize platelet factor 4, a protein relatively specific for platelets, but do not express mRNA transcripts for the fibrinogen, albumin, or IgG found in alpha-granules. We have previously shown that megakaryocytes endocytose circulating proteins, including fibrinogen, albumin, and IgG, and incorporate them into alpha-granules. Thus, platelets appear to contain a unique type of secretory granule whose contents originate by both endogenous synthesis and endocytosis from plasma. Under basal conditions, the source of alpha-granule fibrinogen is plasma.

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