Acts as a ligand for Notch receptors and is involved in somitogenesis. Can activate Notch receptors. Required in somite segmentation to keep the oscillations of neighboring presomitic mesoderm cells synchronized. Strongly expressed in the early retina, where it precedes other delta proteins. Also expressed in cranial ganglia, in sensory epithelia including ear and lateral line and in scattered epidermal cells. In the mesoderm, expression is visible by 50% epiboly; it is expressed subsequently in the tail bud, in stripes in the presomitic mesoderm and in the posterior half of each somite. Also expressed in notochord, blood vessels and pronephros. In contrast to other delta proteins, it is not expressed in the majority of nascent primary neurons. In somites, it marks the posterior part of each formed somite, while deltaD (dld) marks the anterior part. Ubiquitinated by mib, leading to its endocytosis and subsequent degradation.