# Cone subtype specification in human retinas and organoids

> **NIH NIH R01** · JOHNS HOPKINS UNIVERSITY · 2022 · $516,949

## Abstract

Project Summary: The specification of three cone photoreceptor subtypes enables high-acuity daytime and
trichromatic color vision in humans. During terminal differentiation, cone cells express opsins that define their
functionalities as blue (S-opsin), green (M-opsin), or red (L-opsin) light detectors. How the three cone subtypes
are generated in humans remains largely unknown. Elucidating these mechanisms will be critical for
understanding and treating visual disorders including macular degeneration, cone dystrophy, retinitis
pigmentosa, foveal hypoplasia, and color blindness. The goal of this project is to determine the mechanisms
controlling the specification of S, M, and L cones in the human retina.
 Cone subtype specification occurs in a two-step process. First, a decision occurs between S and L/M
cone fates. If the L/M fate is chosen, a subsequent choice is made between L and M cone fates. To study these
processes, we genetically and pharmacologically manipulated human retinal organoids to test mechanisms of
retinal development. We found that dynamic expression of thyroid hormone (TH)-regulating genes within the
retina ensures low TH signaling early to specify S cones and high TH signaling late to produce L/M cones. Our
work established human retinal organoids as a model for determining mechanisms of human development with
promising utility for therapeutics and vision repair (Eldred et al., 2018, Science).
 We found that S, M, and L cones are generated in a temporal progression during development. How
temporal and spatial inputs are integrated in the human retina to generate patterns of cones is poorly understood.
We developed dissection, imaging, and cell identification approaches to assess the spatial distributions of cone
subtypes and generate the first maps of cone subtypes across intact human retinas (Aim 1). We found that
temporal regulation of TH signaling is critical for establishment and maintenance of cone subtype fates. To
evaluate thyroid dysregulation and cone fate plasticity, we will define the temporal windows of TH regulation in
organoids and examine cone fates in retinas from patients with late-onset thyroid dysregulation. We will
determine the roles of TH-regulating genes in cone subtype specification in organoids (Aim 2). Additionally, we
found that retinoic acid (RA) signaling induces S cone fate and suppresses L/M cone fate early in decision 1,
and induces L cone fate and suppresses M cone fate late in decision 2. We will characterize temporal windows
of RA action and assess the function and expression of RA-regulating genes in the specification of cone subtype
fates in organoids (Aim 3).
 These experiments will delineate how regulation of TH and RA signaling specify cone subtypes in the
human retina. Moreover, these experiments will provide the first direct mechanistic insight into L and M cone
specification with important implications for understanding red/green color blindness and developing
regenerative therapeutics...

## Key facts

- **NIH application ID:** 10327705
- **Project number:** 5R01EY030872-03
- **Recipient organization:** JOHNS HOPKINS UNIVERSITY
- **Principal Investigator:** Robert John Johnston
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $516,949
- **Award type:** 5
- **Project period:** 2020-01-01 → 2023-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10327705

## Citation

> US National Institutes of Health, RePORTER application 10327705, Cone subtype specification in human retinas and organoids (5R01EY030872-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10327705. Licensed CC0.

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