Essential to the formation of horizontal top connectors between outer hair cell stereocilia. Strongly expressed in the inner ear, detected in the testis, and barely detected in the eye. Detected in the six sensory areas of the inner ear by immunofluorescence. Expressed only in the sensory hair cells and associated with the stereocilia, the stiff microvilli forming the structure for mechanoreception of sound stimulation. Belongs to the stereocilin family.