Angiopoietin 1 and Angiopoietin 2 are important for development of the endothelium, by regulating tyrosine phosphorylation of the membrane receptor Tie 2/Tek. Angiopoietin 2 is only 60% homologous with Angiopoietin 1. Angiopoietin 1 binding to Tie 2/Tek causes phosphorylation of the receptor. Angiopoietin 2 competes for this binding, and thus blocks receptor phosphorylation. Angiopoietin 2 expression occurs at sites of vascular remodeling: dorsal aorta and major aortic branches, ovary, placenta and uterus.