FIGURE 1.

Arterial formation–vasculogenesis versus angiogenesis. (A) Formation of the dorsal aorta. Dash lines indicate transverse sections corresponding to the diagrams on the right. At E8.0, Shh (black arrows) released from the notochord (n) triggers VEGF expression in the somite (Sm) and the endoderm (Gut). The angioblasts (Abs, red dots) derived from the lateral plate mesoderm (Lpm) migrate toward the VEGF gradient (pink arrows) and coalesce as an endothelial cord. At E8.5, the dorsal aorta becomes a lumenized vessel connected to the heart (H). The developing vitaline veins and cardinal veins are omitted in this diagram. CC: cardiac crescent. NT: neural tube. (B) Arterial formation during postnatal angiogenesis in the retina. Vascular expansion is regulated by antiogenic sprouting at the vascular front, which is induced by a gradient of VEGF released from the neural bed in the avascular (hypoxic) zone. Artery formation is a process of vascular remodeling of the capillary bed. Red arrows indicate the direction of blood flow.