A role of stochastic phenotype switching in generating mosaic endothelial cell heterogeneity.

Previous studies have shown that biological noise may drive dynamic phenotypic mosaicism in isogenic unicellular organisms. However, there is no evidence for a similar mechanism operating in metazoans. Here we show that the endothelial-restricted gene, von Willebrand factor (VWF), is expressed in a mosaic pattern in the capillaries of many vascular beds and in the aorta.

FOXO1-mediated activation of Akt plays a critical role in vascular homeostasis.

Rationale: Forkhead box-O transcription factors (FoxOs) transduce a wide range of extracellular signals, resulting in changes in cell survival, cell cycle progression, and several cell type-specific responses. FoxO1 is expressed in many cell types, including endothelial cells (ECs). Previous studies have shown that Foxo1 knockout in mice results in embryonic lethality at E11 because of impaired vascular development.

Role of RNA splicing in mediating lineage-specific expression of the von Willebrand factor gene in the endothelium.

We previously demonstrated that the first intron of the human von Willebrand factor (vWF) is required for gene expression in the endothelium of transgenic mice. Based on this finding, we hypothesized that RNA splicing plays a role in mediating vWF expression in the vasculature. To address this question, we used transient transfection assays in human endothelial cells and megakaryocytes with intron-containing and intronless human vWF promoter-luciferase constructs.

Vascular bed-specific regulation of the von Willebrand factor promoter in the heart and skeletal muscle.

A region of the human von Willebrand factor (VWF) gene between -2812 and the end of the first intron (termed vWF2) was previously shown to direct expression in the endothelium of capillaries and a subset of larger blood vessels in the heart and skeletal muscle. Here, our goal was to delineate the DNA sequences responsible for this effect. A series of constructs containing deletions or mutations of vWF2 coupled to LacZ were targeted to the Hprt locus of mice, and the resulting animals were analyzed for reporter gene expression.

Differential roles for ETS, CREB, and EGR binding sites in mediating VEGF receptor 1 expression in vivo.

Vascular endothelial growth factor receptor 1 (VEGFR1) is a marker for endothelial-specific gene expression. We previously reported that the human VEGFR1 promoter (between -748 and +284) contains information for expression in the intact endothelium of transgenic mice. The objective of this study was to dissect the cis-regulatory elements underlying VEGFR1 promoter activity in vitro and in vivo.

A GABP-binding element in the Robo4 promoter is necessary for endothelial expression in vivo.

We recently demonstrated that the 3-kb 5'-flanking region of the human ROBO4 gene directs endothelial cell-specific expression in vitro and in vivo. Moreover, a GA-binding protein (GABP)-binding motif at -119 was necessary for mediating promoter activity in vitro. The goal of the present study was to confirm the functional relevance of the -119 GABP-binding site in vivo.

Thrombospondin-1 selectively inhibits early-stage carcinogenesis and angiogenesis but not tumor lymphangiogenesis and lymphatic metastasis in transgenic mice.

The roles played by the endogenous angiogenesis inhibitor thrombospondin-1 (TSP-1) in the early stages of multi-step carcinogenesis and in the control of hematogenous versus lymphatic metastasis are unknown. To investigate these issues we compared tumor development in normal mice and in transgenic mice with targeted overexpression of TSP-1 in the epidermis following a standard two-step chemical skin carcinogenesis regimen. Overexpression of TSP-1 resulted in delayed and reduced development of premalignant epithelial hyperplasias, but did not inhibit the malignant conversion to squamous cell carcinomas.