Plays a critical role in tooth and hair follicle morphogenesis through regulation of the Notch signaling pathway. May play a role in development or function of the auditory system. Secreted protein which may bind to the cell surface via a membrane receptor. In the organ of Corti, expression at postnatal day 1 (P1) is restricted to the basal region of the stereocilia of inner and outer hair cells (at protein level). Expressed in the organ of Corti at P1 and P7, in cochlear ganglion, stria vascularis and vestibular ends at P7, and in inferior colliculus, remaining brainstem, cerebellum, brain hemispheres and retina at P1, P7 and in the adult. Also detected in adult liver, lung, kidney, intestine and testis but not in heart or skeletal muscle. Truncated N-terminus.