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Fibrinogen is not synthesized by human megakaryocytes
F Louache, N Debili, E Cramer, J Breton-Gorius and W Vainchenker
INSERM U91, Hopital Henri Mondor, Creteil, France.
The origin of platelet fibrinogen is controversial. It may arise from two
sources: (a) exogenously by endocytosis of plasma fibrinogen, or (b)
endogenously by synthesis. We explored the second possibility because we
previously demonstrated that the first mechanism does occur. Fibrinogen
synthesis by human megakaryocytes (MK) was investigated by in situ
hybridization and the polymerase chain reaction (PCR) applied to mRNA. MK
differentiating from marrow CFU-MK were cultured in suspension. In situ
hybridization using the 35S alpha and beta fibrinogen chain anti-sense
riboprobes was totally negative in MK in comparison with negative controls
(lambda phage and alpha and beta fibrinogen chain sense riboprobes). In
contrast, synthesis of fibrinogen was detected by this technique in a
hepatoma cell line (HepG 2). Furthermore, mRNA for alpha and beta chains of
fibrinogen was not detected by the PCR performed on mRNA from cultured MK
enriched to 90% purity, by the immunomagnetic bead technique, even after
Southern blotting of the amplified products. In addition, fibrinogen mRNA
was undetected in marrow MK and in platelets by the same technique, whereas
a specific megakaryocyte gene transcript (GPIb alpha) was easily detected.
These observations demonstrate that the only mechanism responsible for the
presence of fibrinogen in platelets is endocytosis of fibrinogen from
plasma.
Volume 77,
Issue 2,
pp. 311-316,
01/15/1991
Copyright © 1991 by The American Society of Hematology
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