Development of form and function in the mammalian cochlea.

The cochlea possesses specialized features to receive sound signals and to resolve and convert the frequency and intensity components within each signal for auditory perception. It consists of precisely patterned and polarized sensory cells adorned with a highly specialized mechanotransduction apparatus for sensitivity and adaptation, and discrete nonsensory cellular networks for biochemical and mechanical support to drive an integrated cellular response and mechanotransduction. This review summarizes recent discoveries about the roles of FGF, Notch, and Hedgehog signaling and transcriptional factors in the differentiation and patterning of the auditory sensory organ, the Usher complex, and the planar cell polarity pathway in the formation and polarization of mechanotransduction component hair bundles, and the contribution of nonsensory cell networks in the stria vascularis and the sensory region toward the maturation of the mammalian cochlea.