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Blood, 1 September 2008, Vol. 112, No. 5, pp. 1720-1729. Prepublished online as a Blood First Edition Paper on June 17, 2008; DOI 10.1182/blood-2007-09-112748.
Submitted September 14, 2007
CIISA, Lisbon Technical University, Lisboa, Portugal * Corresponding author; email: parkashg{at}usc.edu.
The importance of Notch signaling pathway in the regulation of vascular development and angiogenesis is suggested by the expression of Notch receptors and ligands in vascular endothelial cells and the observed vascular phenotypes in mutants of the Notch receptor or ligands, especially Dll4. DLL4 is specifically expressed in arterial endothelial cells during development, and haplo-insufficiency is embryonically lethal in mice. To address the role of Dll4 in vascular development, we produced mDll4 conditionally overexpressed transgenic mice which were crossed with constitutive recombinase cre lines. Double transgenic embryos displayed grossly enlarged dorsal aortae and died before E10.5, showing a variable degree of premature arteriovenous fusion. Veins displayed ectopic expression of arterial markers. Other defects included reduced vascular sprouting, endothelial cell proliferation and migration. mDll4 overexpression also inhibited VEGF signaling and increased fibronectin accumulation around the vessels. In vitro and in vivo studies of DLL4-FL (Dll4-Full length) in endothelial cells recapitulate many of the mDll4 transgenics findings, including decreased tube formation, reduced vascular branching, fewer vessels, increased pericyte recruitment, and increased fibronectin expression. These results establish the role of Dll4 in arterial identity determination, and regulation of angiogenesis subject to dose and location.
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