title: A disorganized innervation of the inner ear persists in the absence of ErbB2.
abstract: ErbB2 protein is essential for the development of Schwann cells and for the normal fiber growth and myelin formation of peripheral nerves. We have investigated the fate of the otocyst-derived inner ear sensory neurons in the absence of ErbB2 using ErbB2 null mutants. Afferent innervation of the ear sensory epithelia shows numerous fibers overshooting the organ of Corti, followed by a reduction of those fibers in near term embryos. This suggests that mature Schwann cells do not play a role in targeting or maintaining the inner ear innervation. Comparable to the overshooting of nerve fibers, sensory neurons migrate beyond their normal locations into unusual positions in the modiolus. They may miss a stop signal provided by the Schwann cells that are absent as revealed with detailed histology. Reduction of overshooting afferents may be enhanced by a reduction of the neurotrophin Ntf3 transcript to about 25% of wild type. Ntf3 transcript reductions are comparable to an adult model that uses a dominant negative form of ErbB4 expressed in the supporting cells and Schwann cells of the organ of Corti. ErbB2 null mice retain afferents to inner hair cells possibly because of the prominent expression of the neurotrophin Bdnf in developing hair cells. Despite the normal presence of Bdnf transcript, afferent fibers are disoriented near the organ of Corti. Efferent fibers do not form an intraganglionic spiral bundle in the absence of spiral ganglia and appear reduced and disorganized. This suggests that either ErbB2 mediated alterations in sensory neurons or the absence of Schwann cells affects efferent fiber growth to the organ of Corti.
authors.affiliation: Department of Biology and Geology, Baldwin-Wallace College, Berea, OH 44017, USA.
authors.forename: Jacqueline K
authors.initials: JK
authors.lastname: Morris
authors.forename: Adel
authors.initials: A
authors.lastname: Maklad
authors.forename: Laura A
authors.initials: LA
authors.lastname: Hansen
authors.forename: Feng
authors.initials: F
authors.lastname: Feng
authors.forename: Christian
authors.initials: C
authors.lastname: Sorensen
authors.forename: Kuo-Fen
authors.initials: KF
authors.lastname: Lee
authors.forename: Wendy B
authors.initials: WB
authors.lastname: Macklin
authors.forename: Bernd
authors.initials: B
authors.lastname: Fritzsch
mesh_terms: D000818:Animals; D019521:Body Patterning; D003056:Cochlear Nerve / Q000166:cytology / Q000196:embryology; D007758:Ear, Inner / Q000294:innervation* / Q000502:physiology*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009475:Neurons, Afferent / Q000502:physiology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000172:deficiency* / Q000235:genetics
chemical_list: D018719:Erb-b2 Receptor Tyrosine Kinases