# Cellular and Molecular Mechanisms of Cochlear Innervation

> **NIH NIH R01** · GEORGETOWN UNIVERSITY · 2023 · $587,421

## Abstract

PROJECT SUMMARY
 Synaptic connections between spiral ganglion neurons (SGNs) and hair cells in the cochlea are critical
for hearing and lost in many forms of hearing impairment. These synapses form prior to hearing onset and are
activated by supporting cell-induced, intrinsically generated activity that is prominent within the developing
cochlea. This periodic and spontaneous synaptic activity initiates SGN burst firing, which promotes SGN survival,
SGN maturation, and development of frequency tuning in central auditory circuits. Our prior studies revealed an
unexpected role for otic mesenchyme cells (OMCs) in establishing appropriate SGN-hair cell connectivity
through activation of POU3F4, a transcription factor associated with X-linked deafness. POU3F4 is expressed
only by OMCs in the cochlea. We found that, in OMCs adjacent to developing SGNs, POU3F4 upregulates Eph
receptor-A4 (EphA4) to promote SGN fasciculation. Subsequently, we discovered that POU3F4 is also
necessary for SGN survival. Recent data from Ca2+ imaging and single cell RNA sequencing (scRNAseq)
experiments support a model whereby OMCs promote SGN development by regulating spontaneous activity
through POU3F4, insulin-like growth factor (IGF) and Semaphorin (SEMA) signaling. Here, we will test the
hypothesis that expression of these factors by OMCs promotes both prehearing spontaneous activity and the
establishment of hair cell–SGN synaptic connections to enable hearing. This hypothesis will be tested in three
aims. In Aim 1, we will determine the role of POU3F4 and OMCs in generating prehearing spontaneous activity.
In Aim 2, we will define the mechanisms by which SEMA5A inhibits SGN spontaneous activity. In Aim 3, we will
determine how POU3F4 promotes IHC innervation. These studies will incorporate a range of Ca2+ imaging,
physiology, molecular profiling, and tissue culture techniques.
 We and others have documented mechanisms of SGN guidance and survival, but there is still limited
understanding of how SGNs differentiate and form synapses with hair cells. After acoustic overexposure, SGN
cell bodies can survive for long periods of time, but their peripheral processes retract away from the hair cells
without easily reconnecting. At present, how to re-establish these connections is not well understood. Successful
completion of these aims will define how genes expressed by OMCs control the formation of the first synapses
in the auditory pathway. By understanding the mechanisms of cochlear innervation during development, we will
begin to build a “toolbox” that could be used to develop molecular therapies for rewiring the damaged adult
cochlea. This research will also reveal key mechanisms required for the development and regulation of cochlear
spontaneous activity. Since neural activity is recognized as a crucial aspect of circuit formation, it is possible that
activity could be an important consideration in cochlear rewiring.

## Key facts

- **NIH application ID:** 10744569
- **Project number:** 2R01DC016595-06
- **Recipient organization:** GEORGETOWN UNIVERSITY
- **Principal Investigator:** Thomas M Coate
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2023
- **Award amount:** $587,421
- **Award type:** 2
- **Project period:** 2018-07-01 → 2028-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10744569

## Citation

> US National Institutes of Health, RePORTER application 10744569, Cellular and Molecular Mechanisms of Cochlear Innervation (2R01DC016595-06). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10744569. Licensed CC0.

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