Pathology Commons^™

Platelet A-Granule Fibrinogen, Albumin, And Immunoglobulin G Are Not Synthesized By Rat And Mouse Megakaryocytes, Prem Handagama, Daniel A. Rappolee, Zena Werb, Jack Levin, Dorothy F. Bainton

Department of Obstetrics and Gynecology Research Publications

It has been assumed that endogenous synthesis by the platelet precursor cell, the bone marrow megakaryocyte, is the major source of platelet a-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 a-granules. We have previously shown that mega- karyocytes endocytose circulating proteins, including fibrino- gen, albumin, and IgG, and incorporate them into a-granules. Thus, platelets appear to …