Delta-like protein 4 (DLL4) is a type I membrane protein belonging to the Delta/Serrate/Lag2 (DSL) family of Notch ligands. Notch signaling is an evolutionarily conserved pathway that controls cell fate and is required in multiple developmental processes including vascular development, hematopoiesis, somatogenesis, myogenesis, and neurogenesis. Activates NOTCH1 and NOTCH4. Interactions of Notch receptors with their ligands result in reciprocal regulated intramembrane proteolysis (RIP). RIP is a mechanism for transmembrane signal transduction that involves the sequential processing by a disintegrin metalloprotease (ADAM) and then by presenilin/ gamma secretase, resulting in shedding of the extracellular domains and the generation of the soluble ICD signaling fragments, respectively.The Notch ICD translocates to the nucleus and interacts with transcriptional coactivators, resulting in the transcription of target genes. The ICDs of the Notch ligands have also been shown to translocate to the nucleus where they may have a signaling function. Involved in angiogenesis; Negatively regulates endothelial cell proliferation and migration and angiogenic sprouting.Essential for retinal progenitor proliferation.Required for suppressing rod fates in late retinal progenitors as well as for proper generation of other retinal cell types. During spinal cord neurogenesis, inhibits V2a interneuron fate.