Putative Notch ligand involved in the mediation of Notch signaling. Plays an essential role during limb, craniofacial and thymic development. May be involved in myogenesis and in the development of peripheral and central nervous systems. Found to be highest in fetal thymus, epidermis, foregut dorsal root ganglia and inner ear. In 2-weeK-old mice, abundant in heart, lung, thymus, skeletal muscle, brain and testis. Expression overlaps partially with Notch1 expression. At 13 dpc, found in paravertebral vessels and dorsal root ganglia. At 14 dpc, in oropharyngeal epithelium, developing thymus and in the muscles of the tongue. By 15 dpc, in many tissues.