We examined embryonic development of neurons and glia of the cochleovestibular nerve in mouse and chick.
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Otic vesicle-derived neurons and neural crest cell-derived glial cells are intimately associated from early stages of cochleovestibular nerve development.
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Projection of central axons of the cochleovestibular nerve follow precisely within pathways made by migratory neural crest cells.
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Projection of peripheral neurites of the cochleovestibular nerve is accompanied by a wave front of migratory neural crest cell glial progenitor cells.
Abstract
The cochleovestibular (CV) nerve, which connects the inner ear to the brain, is the nerve that enables the senses of hearing and balance. The aim of this study was to document the morphological development of the mouse CV nerve with respect to the two embryonic cells types that produce it, specifically, the otic vesicle-derived progenitors that give rise to neurons, and the neural crest cell (NCC) progenitors that give rise to glia. Otic tissues of mouse embryos carrying NCC lineage reporter transgenes were whole mount immunostained to identify neurons and NCC. Serial optical sections were collected by confocal microscopy and were compiled to render the three dimensional (3D) structure of the developing CV nerve. Spatial organization of the NCC and developing neurons suggest that neuronal and glial populations of the CV nerve develop in tandem from early stages of nerve formation. NCC form a sheath surrounding the CV ganglia and central axons. NCC are also closely associated with neurites projecting peripherally during formation of the vestibular and cochlear nerves. Physical ablation of NCC in chick embryos demonstrates that survival or regeneration of even a few individual NCC from ectopic positions in the hindbrain results in central projection of axons precisely following ectopic pathways made by regenerating NCC.
