ABSTRACT
The complex and intricate network of blood and lymphatic vessels that make up the circulatory system of vertebrates plays a vital functional role, supplying oxygen and nutrients, removing wastes, and serving as the conduit for transport of immune and hormonal cells and factors. As might be expected, the formation, remodeling, and regression of blood and lymphatic vessels is a complex process exquisitely controlled in adults by signals from the adjacent tissues that these vessels serve and their surrounding extracellular matrix. However, during early development, the patterning of major blood and lymphatic vessels and in particular the specification and differentiation of the cells that comprise these vessels are regulated by defined genetic programs. In this chapter, we review current understanding of the origins of the different cellular building blocks of blood and lymphatic vessels and genetic programs that regulate their emergence.
