Developmental expression of thrombin in zebrafish embryos: a novel model to study hemostasis.

A partial cDNA encoding zebrafish prothrombin has been cloned and used as a probe to study the temporal expression of prothrombin mRNA during early embryonic development. The results revealed accumulation of prothrombin mRNA in diverse tissues such as the eyes and myotomes in early embryogenesis. We have also examined the enzymatic activity of thrombin in converting fibrinogen to fibrin in individual embryos at different stages of development. We found that the fibrin-forming activity does not temporally correlate with the first presence of thrombin mRNA in the early stages of embryogenesis, but does correlate with the initiation of blood formation. Our ability to observe the fibrin-forming activity in single individual embryo will facilitate studies on identifying recessive mutations affecting blood coagulation, such as the regulatory gene mutations controlling the clotting factor genes. Furthermore, the observation of thrombin activity will also facilitate studies on the blood coagulation pathways in the early embryogenesis in this zebrafish model.