Acts as a ligand for Notch receptors and is involved in primary neurogenesis and somitogenesis. Can activate Notch receptors, thereby playing a key role in lateral inhibition, a process that prevents the immediate neighbors of each nascent neural cell from simultaneously embarking on neural differentiation. Required in somite segmentation to keep the oscillations of neighboring presomitic mesoderm cells synchronized. Interacts with mib. Expressed in both mesodermal and neuroectodermal regions. In the developing nervous system, it is expressed in overlapping regions with deltaB (dlb) and deltaA (dla); in the neural plate, dld is expressed in patches of contiguous cells with dla, while dlb is confined to scattered cells within those patches that will differentiate as neurons. In somites, it marks the anterior part of each formed somite, while deltaC (dlc) marks the posterior part. In 24 hours embryos, expressed in the hindbrain in stripes adjacent to rhombomere boundaries, but not in the actual boundary cells. Ubiquitinated by mib, leading to its endocytosis and subsequent degradation.