The DLL4 gene provides instructions for making a protein that is part of a signaling pathway known as the Notch pathway, which is important for normal development of many tissues throughout the body. The DLL4 protein attaches to a receptor protein called Notch1, fitting together like a key into its lock. When a connection is made between DLL4 and Notch1, a series of signaling reactions is launched (the Notch pathway), affecting cell functions. In particular, signaling stimulated by DLL4 plays a role in development of blood vessels before birth and growth of new blood vessels (angiogenesis) throughout life.