Vascular development and angiogenesis initially depend on endothelial tip cell invasion, which is followed by a series of maturation steps, including lumen formation and recruitment of perivascular cells. Many studies have shown that Notch signaling is involved throughout embryonic vascular development, including the regulation of tip cell formation, artery/vein patterning, and vascular remodeling. However, the role of Notch signaling in the postnatal vasculature has not been well described. Blocking postnatal Notch results in a highly branched, immature vascular plexus. Vascular plexus maturation is partly regulated by vascular smooth muscle cell (VSMC) coverage, and little is known about the role of Notch in the postnatal perivascular compartment. Therefore, the studies in this dissertation proposed to investigate Notch effectors in VSMCs that modulate vessel maturation during postnatal angiogenesis. To verify that Notch signaling is important for postnatal arterial VSMC coverage and subsequent vessel maturation, the perivascular compartment of pups undergoing retinal angiogenesis was examined following Notch inhibition. This resulted in significantly less arterial VSMC coverage. An angiogenesis-specific microarray panel identified Notch effector genes upregulated in VSMCs in contact with the endothelial Notch ligand Jagged1, which is known to be required for arterial VSMC coverage. One of the upregulated genes was integrin [beta]3, which led to increased surface expression of the integrin heterodimer, [alpha]v[beta]3. Integrin [alpha]v[beta]3 is important for cell adhesion and cell migration. In the vasculature, the only available ligand for [alpha]v[beta]3 is von Willebrand Factor (vWF). Examination of pups undergoing retinal developmental angiogenesis revealed that VSMC coverage co-patterns with accumulation of vWF in the endothelial basement membrane. In a 3-dimensional in vitro tube formation assay, disruption of Notch, [alpha]v[beta]3, or vWF prevented an association between VSMCs and newly formed endothelial tubes. Genetic or pharmacological disruption of Jagged1, [alphav]v[beta]3, or vWF suppressed VSMC coverage of nascent vessels and arterial maturation during vascular development in vivo. Therefore, the findings described in this dissertation define a Notch-mediated interaction between the developing endothelium and VSMCs, leading to adhesion of VSMCs to the endothelial basement membrane and arterial maturatio
