Increased hepatic fibrinogen Bbeta-gene transcription is not enough to increase plasma fibrinogen levels. A transgenic mouse study.
The fibrinogen Aalpha, Bbeta, and gamma polypeptides are encoded by three separate genes, which are arranged in the order gamma-alpha-beta. In order to study the biosynthesis of fibrinogen in vivo we generated a line of transgenic mice carrying extra copies of the fibrinogen beta-gene. To clone the mouse fibrinogen Bbeta-chain gene, a mouse 129 Sv/Ev genomic cosmid library was screened, using the mouse fibrinogen Aalpha-, Bbeta-chain cDNA. A clone containing the complete fibrinogen Bbeta-chain gene including approximately 11-kb of the natural promoter region was identified and subsequently microinjected into mice. Southern blot analysis identified a founder that carried additional copies of the fibrinogen Bbeta-chain gene. Transgenic offspring of this founder were interbred and heterozygous and homozygous transgenic mice were obtained. Northern blot analysis demonstrated approximately a 3-fold increase in fibrinogen Bbeta mRNA in heterozygous mice as compared to wild-type, whereas homozygous transgenic mice showed approximately a 9-fold increase. The levels of the Aalpha and gamma mRNAs in transgenic homozygous mice were not changed as compared to those in wild-type mice. Fibrinogen levels in plasma were not significantly increased in transgenic mice as compared to wild-type mice. These results indicate that: additional copies of the fibrinogen Bbeta-chain gene lead to increased levels of the Bbeta-chain mRNA in the liver; the increased levels of Bbeta-chain mRNA in homozygous overexpression mice do not change the transcription levels of the two other fibrinogen mRNAs in vivo; the absence of an increased plasma fibrinogen level in the transgenic mice indicates that this level is not regulated solely by transcription of the Bbeta-chain gene.
Rezaee
F
F
Department of Vascular and Connective Tissue Research, Gaubius Laboratory, TNO-PG, Leiden, The Netherlands.
Maas
A
A
Verheijen
J H
JH
Koopman
J
J
D000818:Animals; D015152:Blotting, Northern; D005340:Fibrinogen / Q000096:biosynthesis* / Q000235:genetics* / Q000502:physiology; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D021122:Protein Subunits; D012333:RNA, Messenger / Q000096:biosynthesis; D014158:Transcription, Genetic; D015854:Up-Regulation / Q000235:genetics*
C115499:BBeta fibrinogen; D021122:Protein Subunits; D012333:RNA, Messenger; D005340:Fibrinogen