Regulation of blood vessel patterning and guidance

The formation of the vascular system during vertebrate embryonic development is crucial to ensure oxygen and nutrient delivery to all tissues in the organism. Blood vessels are formed by differentiation of primitive mesodermal cells into endothelial cells, which coalesce into primitive tubes that proliferate and migrate to colonize tissues. With the onset of the heart beat and blood flow, primitive vessels are rapidly remodelled into branched networks with a characteristic and reproducible anatomy. The major axial vessels such as the aorta and cardinal veins are common to developing mouse, chick and zebrafish embryos. Formation of a stereotyped architecture ensures efficient oxygen and nutriment delivery and thus function of the vascular system. In addition to growth factor gradients, hemodynamic forces are important in the regulation of pattern formation and cooperate to shape the stereotyped vessel anatomy of vertebrate embryos. In addition, blood vessels are often aligned with nerves and display similar branching patterns in peripheral tissues. The molecular mechanisms regulating common wiring of nerves and blood vessels have attracted considerable interest over the past few years. Developing axons navigate through the embryo by responding to a number of different signals in their immediate environment. Molecules such as Semaphorins, Slits and Netrins and their specific receptors provide key ligand–receptor interactions for this process during both neuronal and vascular development.