# Mechanisms of cell fate specification and competence regulation in photoreceptors

> **NIH NIH R01** · UNIVERSITY OF COLORADO DENVER · 2024 · $507,425

## Abstract

PROJECT SUMMARY:
 Age-related macular degeneration and several other diseases can cause rod and cone photoreceptors to
die. This results in permanent visual impairment because the human retina does not regenerate itself. One
potential way to restore vision is by replacing the lost photoreceptors. Audacious strategies to restore vision
include reprogramming the diseased retina to regenerate its own photoreceptors and directly replacing the lost
photoreceptors from stem cell sources. Implementing these strategies requires specific and efficient methods of
programming cells to become rods and cones. However, we face a major barrier to achieving these therapeutic
strategies due to our limited understanding of the mechanisms that govern how photoreceptors normally develop.
 Most of the undifferentiated progenitor cells of the retina will activate the transcription factor Otx2 and acquire
the potential (or competence) to become photoreceptors and bipolar cell interneurons. These competent Otx2+
cells then choose between rod, cone, and bipolar cell types. This fate decision is controlled in part by the
transcription factors Prdm1 and Vsx2. Loss of Prdm1 profoundly increases bipolar cells at the expense of
photoreceptors. Conversely, Vsx2 mutants lack bipolar cells. Neither photoreceptors nor bipolar cells are
generated when Otx2 is mutated. Therefore, the gene regulatory networks responsible for Otx2, Prdm1, and
Vsx2 expression determine the cell type composition of the retina and its ability to function normally. Our goal is
to decipher how this gene regulatory network functions to control cell fate decisions during retinal development.
 Our first objective is to determine how Otx2 expression, which is necessary for photoreceptor and bipolar
cell competence, is regulated during mouse retinal development. We have identified three non-coding DNA
regulatory elements (enhancers) that are essential for Otx2 expression at different times in development.
Perturbing enhancer function also suggests that they dynamically interact in a tight three-dimensional structure
that allows them to substitute for one another. We will test how these enhancers cooperate and substitute for
each other in normal and perturbed conditions using high-resolution chromosome conformation capture and
other genetic approaches. Our second objective is to understand how Otx2+ cells choose between photoreceptor
and bipolar cell types. We found that deleting the bipolar-specific enhancer of Vsx2 prevented bipolar cell
formation. Our results from mutating this enhancer along with Prdm1 suggested that transient Vsx2 expression
permanently drives bipolar formation. Using a combination of mouse mutants, mutagenesis, misexpression, and
CRISPR inhibition tools, we will determine how Vsx2 and the Vsx2 bipolar enhancer control bipolar fate choice.
 Our experiments will unravel the gene regulatory network that controls photoreceptor and bipolar cell
competence and fate choice. Gaining this knowledg...

## Key facts

- **NIH application ID:** 10880063
- **Project number:** 2R01EY024272-10A1
- **Recipient organization:** UNIVERSITY OF COLORADO DENVER
- **Principal Investigator:** Joseph A Brzezinski
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $507,425
- **Award type:** 2
- **Project period:** 2014-04-01 → 2028-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10880063

## Citation

> US National Institutes of Health, RePORTER application 10880063, Mechanisms of cell fate specification and competence regulation in photoreceptors (2R01EY024272-10A1). Retrieved via AI Analytics 2026-06-01 from https://api.ai-analytics.org/grant/nih/10880063. Licensed CC0.

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