Guidance of Spiral Ganglion Neuron Peripheral Axons by Secreted Semaphorins

Wednesday, October 10, 2012 — Poster Session II
Noon – 2:00 p.m	Natcher Conference Center, Building 45	NIDCD	DEV-3

* FARE Award Winner

Authors

• TM Coate
• MW Kelley

Abstract

During cochlear development, spiral ganglion neuron (SGN) peripheral axons precisely navigate through an array of cell types before selectively synapsing with inner or outer hair cells, but the guidance mechanisms associated with this process are poorly understood. Secreted Semaphorins bind to Neuropilin/Plexin (Nrp/Plxn) co-receptor complexes to regulate diverse aspects of axon motility across the nervous system. Several Sema3s are expressed within the cochlear epithelium at E16.5, when type II SGNs have begun to extend their processes toward the outer hair cells. Nrps 1 and 2, and PlxnA3 are expressed by the SGNs, suggesting that these receptors may respond to secreted Semaphorins expressed by cells in the cochlear epithelium. Genetic loss of secreted Semaphorin signaling leads to excessive outgrowth of SGN peripheral axons into the outer hair cell region. Overall, these data suggest that secreted Semaphorins may normally activate Nrp/Plxn receptors to restrict type I SGN processes to the inner hair cell region. In ongoing studies, we are using live imaging to investigate specific aspects of secreted Semaphorin signaling on SGN peripheral axon motility during cochlear development. We have now established a genetic model where sparse numbers of SGNs and all hair cells are imaged simultaneously using spinning disk confocal microscopy.

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