The Notch receptors and their ligands are highly conserved from invertebrates to mammals. Delta-like 4 (DLL4) is one of four or five Notch ligands identified. The binding to Notch receptor results in the proteolysis of Notch and movement of intracellular portions of Notch into the nucleus. This translocation triggers a series of signaling processes. DLL4 is reported to be essential for the regulation of angiogenesis. In thymus, DLL4 is an essential Notch1 ligand responsible for T cell lineage commitment.