Cloning and tissue expression of the tissue prothrombinase Fgl-2 in the Sprague-Dawley rat

To sequence and characterize the expression of the prothrombinase Fgl-2 in the Sprague-Dawley rat.

Reverse-transcriptase polymerase chain reaction was performed on RNA from spontaneously cycling adult pregnant Sprague-Dawley rats by using specific Fgl-2 primers. The resulting amplicon was also used to screen a rat spleen bacteriophage library and to probe a Northern blot of various tissues. The rat Fgl-2 amino acid sequence was compared with the known sequences in mouse and human.

Fgl-2-specific amplicon bands were observed in the rat brain, kidney, liver, ovary, spleen, and gestational day 22 and postpartum uterus. The rat Fgl-2 cDNA and amino acid sequence were found to be homologous with those of human (86% and 74%, respectively) and mouse (91% and 87%, respectively). Northern blotting demonstrated two different-sized transcripts (1.3 and 3.4 kb), and expression was observed in the cervix, heart, liver, ovary, and nongestational and gestational day 22 myometrium.

Thrombin is classically generated from the cleavage of the proenzyme prothrombin by activated factors V and X. In tissues thrombin appears to be generated by a novel prothrombinase Fgl-2 (fibrinogen-like protein) whose activity is stimulated by proinflammatory mediators. Fgl-2 provides the mechanistic coupling between proinflammatory cytokines and the generation of active thrombin independent of the coagulation cascade. Our studies confirmed the expression of Fgl-2 mRNA in several rat tissues, including the pregnant uterus, where it could play a key role in the initiation of parturition especially in response to local or systemic infection.