Molecular Mechanisms of Ribbon Synapse Formation in the Inner Ear

PROJECT SUMMARY Type I spiral ganglion neurons (SGNs) are the sensory afferents of the inner ear that form ribbon synapses with mechanosensory inner hair cells (IHCs). Each IHC is mono-synaptically innervated by up to 30 SGNs with ribbon synapses on single IHCs forming highly stereotyped gradients of varying properties that correlate with the position of these synapses along the basolateral surface of the cell. The mechanisms that regulate the formation of synapses with different properties and localizations along the basolateral axis of single IHCs are not known. Taking advantage of recent single cell RNA sequencing data sets generated by us and others, I am now able to rigorously test the molecular mechanisms guiding the development, refinement, and function of IHC ribbon synapses. Based on recent studies and my preliminary data, neurexin 3 (NRXN3) stands out as a potential regulator of synapse formation between IHCs and SGNs. In this study I propose to investigate NRXN3 as a potential contributor to IHC-SGN synapse formation using mutant mouse models conditionally lacking Nrxn3 with established assays of in situ hybridization, immunostaining, electrophysiology, electron microscopy, and auditory brainstem recordings. I anticipate that loss or mutation of NRXN3 contributes to the molecular pathogenesis of hearing deficits in humans.