Technical Abstract: Potential role of FAK in blood vessel assembly. The process of vessel assembly can be dissected into discernible steps (A), and there is evidence to suggest that FAK is involved throughout. In FAK-/- mutants (B), blood vessel assembly is arrested during tubulogenesis, suggesting that the primary role of FAK in vascular development is the control of endothelial cell migration and tube formation or perhaps earlier during mesodermal induction. However, FAK has also been shown to mediate PDGF-B signaling in mural cell proliferation and migration, which is necessary for the formation of stable, quiescent vessel structures. Therefore, FAK may have other later roles in vessel assembly, which are not revealed in the FAK-/- mutants due to early lethality. Col1 indicates type I collagen; Cx, connexin; Fn, fibronectin; IHH, Indian Hedgehog; Lm, laminin; Ptc, Patched; Smo, Smoothened; and Vn, vitronectin.