# Evolutionary mechanisms controlling opsin gene expression variation

> **NIH NIH R01** · UNIV OF MARYLAND, COLLEGE PARK · 2020 · $367,047

## Abstract

Project summary
 The source of organismal diversity and the ways in which genotypes result in phenotypes
are key questions for understanding evolution. The genomic mechanisms shaping diversity can
vary across organisms, with species having small population sizes (e.g. humans) shaped by
different evolutionary forces from species having large population sizes (e.g. drosophila). In this
proposal, we focus on African cichlid fishes as they are an ideal model to identify genomic
mechanisms shaping phenotypic diversity and speciation in relatively small populations.
 We will examine the genetic basis of opsin gene expression, which determines visual
sensitivities. African cichlids are colorful, visual animals that show significant differences in spectral
sensitivity, even between closely related species. This is a result of their having seven spectrally
distinct cone opsin genes, with subsets of the genes expressed in three combinations or visual
palettes: short, medium and long. Some species progress from the short to medium to long
palettes as they develop from larvae to juveniles to adults. However, adults of sister taxa can differ
in which palette they express by altering this developmental progression. We have previously
made genetic crosses between species with different palettes and identified four candidate genes
with corresponding regulatory mutations.
 In this proposal, we seek to confirm the role of these regulatory mutations in shaping the opsin
gene regulatory network. We will use in vitro methods (luciferase assays; electron mobility shift
assays) as well as assessments of CRISPR generated mutants (qPCR, RNAseq, in situ
hybridization) to discern how the regulatory mutations alter gene expression. Our preliminary
findings suggest that the opsin gene regulatory network is set up as a series of developmental
switches. Within Lake Malawi cichlids, regulatory mutations arose for three transcription factors
and one opsin. These large (0.4-1kb) indels alter the regulatory domains of these candidate genes,
removing the network links and so switching the developmental state. We hypothesize that these
regulatory indels occurred as the result of mobile transposable elements, with fixation of these
indels in small populations leading to rapid phenotypic divergence. Our goal is to detail how the
regulatory network of the opsin genes has evolved across different species. Evolution of opsin
gene expression could potentially serve as a model for how other cichlid phenotypes diverge.

## Key facts

- **NIH application ID:** 9966544
- **Project number:** 2R01EY024639-06
- **Recipient organization:** UNIV OF MARYLAND, COLLEGE PARK
- **Principal Investigator:** KAREN L CARLETON
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $367,047
- **Award type:** 2
- **Project period:** 2014-08-01 → 2022-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9966544

## Citation

> US National Institutes of Health, RePORTER application 9966544, Evolutionary mechanisms controlling opsin gene expression variation (2R01EY024639-06). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9966544. Licensed CC0.

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