Control of sensory cell differentiation in the inner ear by extracellular signals and transcriptional regulators

The mammalian inner ear contains six mechanosensory organs responsible for detecting sound, linear and angular acceleration. Each organ contains sensory hair cells that respond to mechanical stimulation and form synapses with afferent auditory and vestibular neurons. The precise arrangement of the six sensory organs and the neurons that innervate them is controlled by a variety of extracellular signals that first induce the inner ear, pattern its cardinal axes, and then fix the position of each sensory organ in space. The interplay between successive sets of signals and the transcriptional regulators that mediate their action leads to the formation of morphologically complex yet highly sensitive hearing and balance organs. This chapter will review these signals and regulators, with particular emphasis on the formation of the organ of Corti, the hearing organ of the cochlea, which exhibits one of the most finely patterned cellular arrays in vertebrates.