Requisite Role of Angiopoietin-1, a Ligand for the TIE2 Receptor, during Embryonic Angiogenesis

It is shown that mice engineered to lack Angiopoietin-1 display angiogenic deficits reminiscent of those previously seen in mice lacking TIE2, demonstrating that AngiopOietIn-1 is a primary physiologic ligand for TIE1 and that it has critical in vivo angiogenesis actions that are distinct from VEGF and that are not reflected in the classic in vitro assays used to characterize VEGf.