Signals exchanged between these 2 cell types control the formation, maturation, remodeling, and function of microvascular networks. Mural cells are either pericytes in the microvasculature or smooth muscle cells (SMCs) in larger vessels. Interactions between endothelial cells and mural cells serve to stabilize nascent capillary vessels, provide endothelial cell survival factors, inhibit endothelial cell proliferation, promote mural cell differentiation, and guide vascular network remodeling. 1, 2 Yet precisely how endothelial cells recruit mural cells to form a functional vessel wall is still incompletely understood.