Expression of human fibrinogen in transgenic mice

Human fibrinogen (hfib) is a 340 kDa plasma protein which is a complex precursor substrate to fibrin during clot formation. The present work evaluates the potential of the mammary gland of transgenic mice to coordinately express three separate cDNAs for hfib and then assemble hexameric, functional recombinant human fibrinogen (rhfib). Trigenic mice were made by pronuclear co-microinjection of separate constructs for each cDNA of the Aα, Bβ and γ hfib polypeptides. Each transgene contained a 2.6 kb promoter sequence from the murine whey acidic protein (mWAP). Trigenic mice expressing rhfib at about 5-35 μg/ml milk were generated. The rhfib showed an apparent molecular weight by SDS-PAGE similar to that of hfib under non-reducing conditions. Under reducing conditions, the α-chain of rhfib had slightly greater mobility than α-chain from hfib. The rhfib was converted to fibrin by thrombin in a manner similar to that of hfib where a normal fibrin clot and a lower apparent mobility of the α-chain from the clot relative to the starting precursor chains were observed for both rhfib and hfib. In summary, these results show that functional fibrinogen can be synthesized and secreted by the mammary gland of transgenic mice