Thrombotic phenotype in homozygous E17.5 Pros^−/− embryos. Histologic analysis of E17.5 Pros^−/− embryos demonstrated extensive intracranial hemorrhages (ICH; A-B) and subcutaneous hemorrhages (SCH; C), together with the presence of thrombi (arrows) in the liver (D). Fibrin deposition in E17.5 Pros^−/− livers was evidenced by immunostaining with a polyclonal antibody raised against mouse fibrinogen (E). Histologic analysis also demonstrated an increased number of megakaryocytes in E17.5 Pros^−/− livers (F), secondary to peripheral thrombocytopenia. Together with interstitial fibrin deposition, this suggested consumptive coagulopathy in E17.5 Pros^−/− embryos.