Transcription factors in inner ear development.

The organs of the inner ear are derived from the otic placode, a region of surface and neural ectoderm on the lateral rhombencephalon that invaginates and pinches off to form a closed sack, the otic vesicle (3, 4). Elongations and distortions of the otic vesicle then create the six separate organs of the mammalian inner ear: the sacculus, the utriculus, and the three semicircular canals of the vestibular system, and the snail-shaped cochlea responsible for auditory sensation (Fig. 1). The auditory and vestibular organs are similar in many respects beyond their common embryonic origin. Both use a single mechanosensitive cell type-the hair cell-as the primary receptor cell. In both systems deflection of the hair cell's ciliary bundle is the proximal stimulus; sensitivity to different physical stimuli (linear acceleration, angular velocity, or acoustic stimuli) is conferred by different accessory structures that convey these stimuli to hair cells in the different organs. Yet there are differences as well: the sensory epithelium in vestibular organs is roughly oval and contains hair