TARGETING OF TRANSGENE EXPRESSION TO THE VASCULAR ENDOTHELIUM OF MICEBY HOMOLOGOUS RECOMBINATION AT THE THROMBOMODULIN LOCUS

We describe a straightforward gene-targeting technique to achieve unif orm, stable, and genetically invariant expression of a transgene in th e vascular endothelium of mice. To demonstrate the feasibility of this approach, the reporter gene bacterial P-galactosidase was inserted vi a 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 promote r. The expression of the transgene in adult mice recapitulated the wid espread, stable, and high-level expression of the thrombomodulin gene in vascular endothelium. These data indicate that targeting of cDNAs i nto the thrombomodulin locus serves as a viable strategy to express tr ans-genes in endothelial cells. Analysis of reporter gene expression r evealed a heterogeneous pattern of thrombomodulin gene activity in the endothelium of the aorta and its tributaries. We also show that embry onic stem cells with a targeted thrombomodulin locus contribute in a m osaic fashion to the vascular endothelium of chimeric mice. This metho d for generating animals with a functionally heterogeneous cardiovascu lar system should provide an experimental technique for studying how l ocalized genetic abnormalities in endothelial cell function lead to th e development of vascular diseases.