# Molecular determinants of cell fate in the inner ear

> **NIH NIH R01** · UNIVERSITY OF MISSISSIPPI MED CTR · 2021 · $324,063

## Abstract

Project Summary:
Hearing is a vital sense for nearly all animals, including humans. In mammals, the organ of Corti transduces
sound into neural signaling and is well-known for the elegant arrangement of cochlear hair cells into one row of
inner hair cells (IHCs) and three rows of outer hair cells (OHCs). This marvel of cellular architecture has
appeared in nearly every biology textbook since its description in 1851, yet how IHCs and OHCs differentiate
from one another during development is still poorly understood. Hearing loss resulting from inherited
mutations and from the loss of hair cells with age, noise, or other insults, affects millions of Americans and
countless more globally. In addition, mammalian HCs do not regenerate, and although genetic manipulations
suggest that stem cells or nonsensory cells may be converted into cells that resemble hair cells, these cells
remain underdeveloped and do not differentiate into mature IHCs or OHCs. Thus, understanding how IHCs
and OHCs become distinct cells with complementary functions is of fundamental importance to our
understanding of developmental biology and the design of potential otoprotective and regenerative therapies.
In this application, we present preliminary evidence that two gene products, p27Kip1 and SIX2, are critical
mediators of cell fate decisions leading to IHC and OHC fates, respectively, during cochlear maturation. To test
whether p27Kip1 inhibits OHC fate, we propose to delete p27Kip1 from cochlear hair cells, in vivo, and examine
the IHCs to see if they adopt OHC characteristics. Conversely, we propose to ectopically express p27 Kip1 in
cochlear HCs to test whether exogenous p27Kip1 prevents OHCs from fully differentiating, or causes them to
become IHC-like. We further propose to similarly manipulate the expression of Six2 in IHCs and OHCs to see
whether the loss of Six2 from OHCs promotes an IHC fate, or if ectopic Six2 expression in IHCs promotes an
OHC fate. The altered cell fates in each of these models will be examined by several means including confocal
microscopy of fluorescent reporter proteins and immunofluorescent staining to visualize the expression of
various proteins that are known to be specific to either IHCs or OHCs. Fluorescent immunostaining will also be
used to examine the types of innervation and synaptic connections exhibited by the cells. Sorting of small pools
of IHCs and OHCs from each of these models followed by whole transcriptome gene expression analysis (RNA-seq) will further provide an in-depth characterization of the extent of phenotypic conversion of the cells.
Finally, scanning electron microscopy will be used to compare the morphological characteristics of the
stereociliary bundles which typically differ between IHCs and OHCs. These experiments will allow us to
determine whether p27Kip1 and/or SIX2 are critical determinants of IHC and OHC fate and positive results will
strongly support future investigation of the roles played by these molecules ...

## Key facts

- **NIH application ID:** 10194453
- **Project number:** 5R01DC016365-05
- **Recipient organization:** UNIVERSITY OF MISSISSIPPI MED CTR
- **Principal Investigator:** Bradley J. Walters
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $324,063
- **Award type:** 5
- **Project period:** 2017-07-01 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10194453

## Citation

> US National Institutes of Health, RePORTER application 10194453, Molecular determinants of cell fate in the inner ear (5R01DC016365-05). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10194453. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*