Axon guidance in the chicken inner ear

Andrea Campero Battisti, Purdue University

Abstract

The mechanosensory hair cells in the chicken inner ear are innervated by bipolar afferent neurons. During development each neuron migrates to its final position in either the auditory or vestibular ganglion, while it simultaneously sends a central process to the hindbrain and a peripheral process to only one of the eight distinct sensory organs. Very little is known about the decision points and cues that regulate the establishment of the peripheral projections of auditory and vestibular ganglion neurons. Our hypothesis is that auditory and vestibular axons respond to different attractants and/or repellents as they explore the periphery. We therefore sought to determine the expression of a known family of axonal repellents, the Slits and Robos, in the chicken inner ear during development. Our data suggest slit and robo mRNAs are expressed at the right time and location to potentially play multiple roles during inner ear development. We speculate that Slit and Robo interactions could be involved in neuroblast migration from the otocyst, axon repulsion of otic or non-otic neurons, and/or the maintenance of sensory-nonsensory boundaries. To investigate the role(s) of Slit in the chicken inner ear, we used a gain-of-function approach and misexpressed Slit in the ear and in vitro to seek evidence of otic axon responsiveness to Slits. By electroporating Slit into the prosensory primordia of the cristae, regions that do not normally express endogenous Slit, we were able to assay whether otic axons respond to ectopic Slit. Our in vivo data suggest anterior crista afferents, but not posterior crista afferents, are repelled by Slit. We therefore speculate subsets of otic neurons differentially respond to this guidance cue; our in vitro data do not contradict this conclusion. This study thus provides the first evidence that at least a subset of otic afferents respond to Slit as they are pathfinding to their peripheral targets in the ear.

Degree

Ph.D.

Advisors

Fekete, Purdue University.

Subject Area

Neurosciences

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