Vascular morphogenesis: a Wnt for every vessel?

Blood vessel development requires orchestrated activities of heterogeneous endothelial cell (EC) populations to create a hierarchically branched tubular network. Endothelial heterogeneity is manifested in organ-specific endothelial differentiation and function in the mature vasculature. During sprouting angiogenesis, ECs are specified by Dll4/Notch signalling into leading tip cells and following stalk cells, which together through coordinated migration and proliferation shape the nascent vascular sprout. Wnt-signalling influences many aspects of branching tubulogenesis in various species and organ systems, often in coordination with Notch signalling. Recent advances in vascular biology highlight important roles for multiple components of the Wnt-signalling pathway in regulating cell differentiation, proliferation, survival, cell junctions and polarity. Here, we review the emerging concepts of the molecular actions of Wnt-signalling in regulating differential behaviour and/or cell functions during vascular development.