Prothrombin mRNA is expressed by cells of the nervous system

Thrombin, a serine protease of the blood coagulation system, has additional effects on cells in vitro. It is mitogenic for fibroblasts and astrocytes and contributes to the regulation of neurite outgrowth and astrocyte stellation. Until now the expression of thrombin or its precursor prothrombin in tissues other than liver has not been demonstrated conclusively because of difficulty in avoiding serum contamination. Using sensitive mRNA detection methods, we show here that prothrombin is expressed not only in the liver, but also in the brain throughout development. Polymerase chain reaction, Northern, and in situ hybridization studies demonstrate the presence of prothrombin transcripts in the olfactory bulb, the cortex, the cerebellum, and other regions of the rat and human nervous system, as well as in neural cell lines. These results support an involvement of (pro)thrombin in the regulation of cellular events in the nervous system.