F9, also known as F9 p22 and FIX (coagulationfactor IX), is also located on the X chromosome like F8. It encodes a vitamin K-dependent serine protease (factor IX), which plays a key role in the intrinsic coagulation pathway. The zymogen is activated by XIa factor to obtain factor IXa, and then the inactive factor X is activated to factor Xa by the participation of factor VIIIa, calcium ions, and membrane phospholipids, and then the coagulation reaction continues. Deletion of the F9 gene leads to factor IX deficiency, which triggers coagulopathy and is hemophilia B with X-chromosome recessive inheritance, and it can be said that the F9 gene is of extraordinary significance for the study of hemophilia B.

The experimental animals were randomly divided into groups and given NS (normal saline) or 3 mg/kg NovoSeven by tail vein injection, 30 minutes after injection of the drug, blood was collected from the abdominal aorta to detect the blood coagulation index: activated partial thromboplastin time APTT, Fibrinogen FIB.

The results showed that APTT values in B-F9 KO mice (male) were much higher than those in WT mice (male), and APTT returned to normal values after injection of ovoSeven (recombinant human coagulation factor VIIa). And there was no significant difference in FIB values between B-F9 KO mice and WT mice. The results showed that B-F9 KO mice can be used as a powerful tool for the validation of anticoagulant efficacy.