Acts as a ligand for Notch receptors and is involved in primary neurogenesis. 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 for boundary formation during segmentation of the hindbrain. Required for midline cell fate specification prior to germ layer formation; regulates specification of floorplate, notochord and hypochord. In inner ear, it prevents adjacent cells from adopting the same cell fate. Plays a role in angiogenesis. Interacts with mib. Expressed in nervous system. In the developing nervous system, it is expressed in overlapping regions with deltaB (dlb) and deltaD (dld); in the neural plate, dla is expressed in patches of contiguous cells with dld, while dlb is confined to scattered cells within those patches that will differentiate as neurons. In 24 hours embryos, expressed in the hindbrain in stripes adjacent to rhombomere boundaries, but not in the actual boundary cells. During gastrulation and tail formation, expressed in embryonic midline cells. Expressed in hair cells of inner ear. Initiated in the neuroectoderm before that of dld. In the developing trunk neural plate and neural tube, it is initiated in the epiblast prior to completion of gastrulation. At the 2- to 3-somite stage (10.5 hours) low levels are distributed throughout the trunk CNS, with cells expressing higher levels found in the medial and lateral regions of the neural plate. These regions correspond to the positions at which primary motoneurons and Rohon Beard neurons (RBs) originate. Cells expressing high levels do not form contiguous domains. Rather, single cells or small clusters of several cells showing high expression are interspersed with cells having lower expression. Expression is specific to the developing nervous system, and continues to be expressed broadly in the CNS throughout neurogenesis. Expressed in cells specified for neuronal fates. At 24 hours, and throughout later embryogenesis, it is broadly expressed in the spinal cord, suggesting that it is expressed by many types of cells. Expressed as neuronal specification occurs and is subsequently down-regulated in cells that have acquired specific neuronal fates. Ubiquitinated by mib, leading to its endocytosis and subsequent degradation.