Development of the semicircular canals and otolithic organs of the vertebrate inner ear

The vestibular apparatus of the inner ear functions to sense gravity and motion. Working together with the visual and proprioceptive systems via various muscular reflexes, it enables an organism to stabilise head position, gaze and body posture, both at rest and during movement. These functions are dependent on sensory hair cells that respond to mechanical stimulation, together with their associated non-sensory structures, including fluid-filled ducts and chambers, specialised extracellular matrices, and biomineralised crystalline deposits. The focus of this review is on the embryonic development of selected elements of the vestibular system: morphogenesis of the semicircular canal ducts, development of the ampullae and sensory cristae, and formation of the biomineralised otoliths and otoconia. Recent findings have identified new genetic players, dynamic cross-repressive gene regulatory networks, and morphogenetic mechanisms that act to shape the developing vestibular system. A final section of the review highlights approaches that link developmental genetic studies to an understanding of cell and tissue mechanics, vestibular-driven behaviour, evolution and human disease.