The Development of Blood Vessels: Cellular and Molecular Mechanisms

All blood vessels share a common function to deliver oxygen to and remove metabolites from peripheral tissues. However, we now know that not all vessels are alike. In fact, they significantly differ in many respects. For instance, some only consist of endothelial cells (capillaries), while others are surrounded by smooth muscle cells (arteries, veins). Arteries differ from veins by the number of smooth muscle cells, but even capillaries without smooth muscle cells express selective arterial or venous markers. Various arteries differ by the embryonic origin of their smooth muscle cells. But even arteries and veins in different organs express specific markers and have specialized functions to accommodate the distinct needs in each organ. Furthermore, vessels in an embryo are actively growing in an ordered pattern and are quiescent in a healthy adult, but they are completely chaotic and growing in an uncontrolled manner in a sick patient with a tumor. Genetic analysis over the last 10 years has provided stunning insights in the cellular and molecular mechanisms that define the formation and function of these distinct vessels. These insights are discussed in this overview.