Cochlear development: hair cells don their wigs and get wired.
OBJECTIVE
Hair cells and spiral ganglion neurons form functional pairings in the cochlea that transduce the mechanical energy of sound into signals that are carried to the brainstem. Mutations of genes affecting the development and maintenance of these two cell populations cause deafness in humans and other animals. This review highlights recent findings regarding the development of hair cell stereocilia and spiral ganglion neurons in the cochlea.


RESULTS
Genes underlying Usher syndrome 1A have shed light on possible molecular participants in the development and structure of the hair cell stereocilia. Analysis of deaf mouse mutants have uncovered genes involved in stereocilia elongation and the orientation of the stereociliary bundles. Studies on the regulation of spiral ganglion neuronal survival and guidance suggest that the timing of expression of specific growth factors along the cochlear spiral is involved in maintaining the divergence of vestibular and cochlear nerve fibers.


CONCLUSIONS
Examining human and mouse genes affecting hearing has not only provided insight into causes of human deafness, but has also opened a window into how stereociliary bundles are constructed and spiral ganglion neurons are preserved and guided during development. Synthesis of information from diverse lines of research pinpoints genes for screening or repair in the genetic medicine of the future and dramatizes the intimate relationship between strict adherence to complex developmental programs and hearing. In addition, future improvements in the efficacy of cochlear implants may depend on the preservation and manipulation of adult spiral ganglion neurons. Developmental mechanisms promise to yield insight into possible interventions to redirect or reconnect spiral ganglion neurons in damaged cochlea.
Whitlon
Donna S
DS
Department of Otolaryngology, Head and Neck Surgery and Institute for Neuroscience, Feinberg School of Medicine, Northwestern University, 303 E. Chicago Avenue, Searle Building 561, Chicago, IL 60611, USA. whitlon@northwestern.edu
D000818:Animals; D001489:Basilar Membrane / Q000033:anatomy & histology / Q000502:physiology; D002923:Cilia / Q000502:physiology; D003051:Cochlea / Q000196:embryology* / Q000502:physiology; D003056:Cochlear Nerve / Q000502:physiology; D018069:Hair Cells, Vestibular / Q000196:embryology / Q000502:physiology*; D006309:Hearing / Q000502:physiology*; D006801:Humans; D051379:Mice; D012680:Sensitivity and Specificity; D013136:Spiral Ganglion / Q000196:embryology / Q000502:physiology*; D013137:Spiral Lamina / Q000502:physiology*