# IRX in epidermal differentiation

> **NIH NIH F30** · UNIVERSITY OF CALIFORNIA-IRVINE · 2020 · $45,520

## Abstract

PROPOSAL SUMMARY
Epidermal differentiation is critical for health with differentiation defects underlying skin diseases in children,
including the common Atopic Dermatitis. Epidermal differentiation is a complex process in which enhancers,
epigenetic changes, and transcription factors coordinately regulate the expression of structural proteins,
adhesion molecules, and lipid producing enzymes necessary for epidermal barrier formation. Dramatic gene
expression changes observed in differentiation correspond to large-scale reorganization of epigenetic regulator
structures such as super-enhancers, which preferentially drive expression of genes vital for cell identity. In
recent experiments, we have studied the dynamics of enhancer formation during differentiation of human
keratinocytes. Within the super-enhancer encompassing the gene body of Grhl3, a key regulator of epidermal
differentiation, we identified enriched binding sites for IRX, a transcription factor with unknown roles in the
epidermis, suggesting that IRX may promote epidermal differentiation. Consistent with this idea, we found that
the temporal expression of several IRX factors in mouse epidermal development mirrors that of known
regulatory transcription factors for epidermal differentiation, including GRHL3. Depletion of GRHL3 in
keratinocytes changes the enhancer landscape with formation of new non-keratinocyte super-enhancers that
promote neuronal cell fate. Intriguingly, these newly formed enhancers exhibit striking overrepresentation of
IRX binding sites, suggesting that GRHL3 may suppress the tendency of keratinocytes to exhibit neuronal-type
features. The temporal expression pattern of several Irx genes in mouse epidermal development is similar to
that of well-known epidermal differentiation. Single cell analysis of newborn mice epidermis unveiled a gradient
of Irx3 expression that correlates with the keratinocyte's degree of differentiation. These preliminary results
suggest that IRX plays a key role in epidermal differentiation. The hypothesis is that an interplay between
GRHL3 and IRX promotes epidermal differentiation through at least two different mechanisms: 1) both IRX and
GRHL3 activate genes expressing epidermal differentiation factors, and 2) GRHL3 suppresses the formation of
IRX-sensitive SEs that otherwise would activate non-epidermal, neuronal genes in the differentiating
epidermis. Two Aims are proposed to test the hypothesis: Aim 1 will utilize an in vitro model of human
epidermal keratinocyte differentiation to provide insights into the mechanism whereby IRX regulates
differentiation. Aim 2 will utilize conditional Irx3;Irx5 double knockout mice to characterize the epidermal
differentiation phenotype of mice deficient for Irx3 and Irx5 in the epidermis. This work will establish the role of
IRX in skin development and elucidate how GRHL3 and IRX collaborate in epidermal differentiation.

## Key facts

- **NIH application ID:** 9973225
- **Project number:** 5F30HD093392-04
- **Recipient organization:** UNIVERSITY OF CALIFORNIA-IRVINE
- **Principal Investigator:** Jefferson Chen
- **Activity code:** F30 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $45,520
- **Award type:** 5
- **Project period:** 2017-08-01 → 2022-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9973225

## Citation

> US National Institutes of Health, RePORTER application 9973225, IRX in epidermal differentiation (5F30HD093392-04). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9973225. Licensed CC0.

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