A murine model of myocardial microvascular thrombosis.

Disorders of hemostasis lead to vascular pathology. Endothelium-derived gene products play a critical role in the formation and degradation of fibrin. We sought to characterize the importance of these locally produced factors in the formation of fibrin in the cardiac macrovasculature and microvasculature.

Structure-function analyses of thrombomodulin by gene-targeting in mice: the cytoplasmic domain is not required for normal fetal development.

Thrombomodulin (TM) is a widely expressed glycoprotein receptor that plays a physiologically important role in maintaining normal hemostatic balance postnatally. Inactivation of the TM gene in mice results in embryonic lethality without thrombosis, suggesting that structures of TM not recognized to be involved in coagulation might be critical for normal fetal development. Therefore, the in vivo role of the cytoplasmic domain of TM was studied by using homologous recombination in ES cells to create mice that lack this region of TM (TMcyt/cyt).

A targeted point mutation in thrombomodulin generates viable mice with a prethrombotic state.

The activity of the coagulation system is regulated, in part, by the interaction of thrombin with the endothelial cell receptor thrombomodulin with subsequent generation of activated protein C and suppression of thrombin production. Our previous investigation demonstrated that ablation of the thrombomodulin gene in mice causes embryonic lethality before the assembly of a functional cardiovascular system, indicating a critical role for the receptor in early development. In the current study, we show that a single amino acid substitution in thrombomodulin dissociates the developmental function of the receptor from its role as a regulator of blood coagulation.

Thrombomodulin modulates growth of tumor cells independent of its anticoagulant activity.

Thrombomodulin (TM), recognized as an essential vessel wall cofactor of the antithrombotic mechanism, is also expressed by a wide range of tumor cells. Tumor cell lines subcloned from four patients with malignant melanoma displayed a negative correlation between TM expression and cell proliferation in vitro and in vivo. Overexpression of wild-type TM decreased cell proliferation in vitro and tumor growth in vivo.

Vascular bed-specific expression of an endothelial cell gene is programmed by the tissue microenvironment.

The endothelium is morphologically and functionally adapted to meet the unique demands of the underlying tissue. At the present time, little is known about the molecular basis of endothelial cell diversity. As one approach to this problem, we have chosen to study the mechanisms that govern differential expression of the endothelial cell-restricted von Willebrand factor (vWF) gene.

Developmentally regulated gene expression of thrombomodulin in postimplantation mouse embryos.

Embryonic lethality of thrombomodulin-deficient mice has indicated an essential role for this regulator of blood coagulation in murine development. Here, the embryonic expression pattern of thrombomodulin was defined by surveying beta-galactosidase activity in a mouse strain in which the reporter gene was placed under the regulatory control of the endogenous thrombomodulin promoter via homologous recombination in embryonic stem cells. The murine trophoblast was identified as a previously unrecognized anatomical site where TM expression is conserved between humans and mice and may exert a critical function during postimplantation development.

Targeting of transgene expression to the vascular endothelium of mice by homologous recombination at the thrombomodulin locus.

We describe a straightforward gene-targeting technique to achieve uniform, stable, and genetically invariant expression of a transgene in the vascular endothelium of mice. To demonstrate the feasibility of this approach, the reporter gene bacterial beta-galactosidase was inserted via homologous recombination into the intronless thrombomodulin locus of murine embryonic stem cells. In this fashion, the lacZ gene is placed under the regulatory control of the endogenous thrombomodulin promoter.

Human von Willebrand factor gene sequences target expression to a subpopulation of endothelial cells in transgenic mice.

The present study was undertaken to define the 5' and 3' regulatory sequences of human von Willebrand factor gene that confer tissue-specific expression in vivo. Transgenic mice were generated bearing a chimeric construct that included 487 bp of 5' flanking sequence and the first exon fused in-frame to the Escherichia coli lacZ gene. In situ histochemical analyses in independent lines demonstrated that the von Willebrand factor promoter targeted expression of LacZ to a subpopulation of endothelial cells in the yolk sac and adult brain.

Thrombomodulin gene regulation by cAMP and retinoic acid in F9 embryonal carcinoma cells.

Thrombomodulin (TM) expression was investigated during differentiation of F9 embryonal carcinoma cells into primitive or parietal endoderm. Exposure of F9 cells to retinoic acid (RA) triggers differentiation into primitive endoderm and induces the appearance of barely detectable amounts of TM mRNA, whereas treatment with dibutyryl cAMP plus theophylline (CT) augments the levels of TM mRNA to a 4-fold greater extent than RA. Exposure of F9 cells to RA plus CT initiates differentiation into parietal endoderm and synergistically increases the levels of TM mRNA by 10- to 12-fold compared with CT.