Cited by 126melanin and skin pigmentationZebrafish Biomedical Research ApplicationsDevelopmental Biology and Gene Regulation

The DOI matches its Crossref record; 114 of the 114 references it cites were found in a registry or an index; 53 of the 93 sources its claims cite were checked for support.

Gene Expression Analysis of Zebrafish Melanocytes, Iridophores, and Retinal Pigmented Epithelium Reveals Indicators of Biological Function and Developmental Origin

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Abstract

In order to facilitate understanding of pigment cell biology, we developed a method to concomitantly purify melanocytes, iridophores, and retinal pigmented epithelium from zebrafish, and analyzed their transcriptomes. Comparing expression data from these cell types and whole embryos allowed us to reveal gene expression co-enrichment in melanocytes and retinal pigmented epithelium, as well as in melanocytes and iridophores. We found 214 genes co-enriched in melanocytes and retinal pigmented epithelium, indicating the shared functions of melanin-producing cells. We found 62 genes significantly co-enriched in melanocytes and iridophores, illustrative of their shared developmental origins from the neural crest. This is also the first analysis of the iridophore transcriptome. Gene expression analysis for iridophores revealed extensive enrichment of specific enzymes to coordinate production of their guanine-based reflective pigment. We speculate the coordinated upregulation of specific enzymes from several metabolic pathways recycles the rate-limiting substrate for purine synthesis, phosphoribosyl pyrophosphate, thus constituting a guanine cycle. The purification procedure and expression analysis described here, along with the accompanying transcriptome-wide expression data, provide the first mRNA sequencing data for multiple purified zebrafish pigment cell types, and will be a useful resource for further studies of pigment cell biology.

Overview

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Written from the paper’s full text.

TL;DR

The authors developed a density-gradient/FACS method to purify zebrafish melanocytes, iridophores, and retinal pigmented epithelium (RPE) and generated the first transcriptome-wide mRNA sequencing data for these three pigment cell types, including the first iridophore transcriptome. Comparative expression analysis identified shared and cell-type-specific gene sets, notably a guanine-synthesis cycle model in iridophores.

Key findings

  • RNA-seq detected 8,472 genes expressed in melanocytes, 8,096 in iridophores, and 9,053 in RPE at >1 RPKM; melanocyte–RPE expression was most correlated (r = 0.90), while melanocyte–iridophore and RPE–iridophore correlations were modest (r = 0.52 and r = 0.49), and each pigment cell type correlated with whole embryos at <0.02.
  • The authors found 214 genes co-enriched in melanocytes and RPE, 62 co-enriched in melanocytes and iridophores, and only one gene, alcama, co-enriched in RPE and iridophores; 28 genes were shared among all three pigment cell types at ≥4 RPKM, within 2-fold of each other, and ≥100-fold above whole embryos.
  • Iridophores showed extensive enrichment of guanine-production machinery: 5 glucose transporters, 7/11 glycolysis steps, and 9/9 de novo purine synthesis enzymes were enriched; impdh1b was 71-fold higher than in melanocytes, prtfdc1 was 198-fold higher, and the adenine-specific adssl was not significantly different from melanocytes (0.7-fold).
  • The iridophore-enriched list included 346 genes, with 30 genes expressed at least 30-fold above melanocytes and RPE and 100-fold above whole embryos; the authors propose a guanine cycle model in which PRPP is recycled during guanine pigment production.

Methods

  • Zebrafish homozygous for temperature-sensitive mitfavc7 were dissociated, pigment cells enriched by Percoll density gradient centrifugation, and sorted by FACS using iridophore autofluorescence; mRNA was extracted and Illumina cDNA libraries were sequenced for 11 melanocyte, 5 iridophore, and 5 RPE samples, plus whole 3 dpf embryos.
  • Sequence tags were aligned with Novoalign to a custom non-redundant database of 25,102 zebrafish genes; expression was normalized as RPKM, statistical tests were performed in R, and selected expression changes were validated by qRT-PCR.
  • Enrichment analyses used a 1 RPKM baseline and thresholds including ≥2-fold over the third cell type with p<0.05, ≥8-fold over whole embryos for co-enrichment/cell-specific genes, and stricter cutoffs for selected shared or iridophore-specific gene lists.

Limitations

  • Stated: mitfa may be partially compromised by aberrant splicing at permissive temperatures, though melanocytes appeared indistinguishable from wild-type; RPE preparations lacked separate markers for eye-associated neural crest-derived melanocytes or choroidal melanocytes, and one RPE library was prepared later than 5 dpf.
  • Stated: the authors did not have statistical power to confidently track developmental changes in gene expression within specific cell types, and xanthophores were not isolated by the procedure.
  • Evident: the method relies on density and autofluorescence rather than lineage markers, so purity depends on those physical properties; the reduced-representation cDNA strategy could miss short cDNAs lacking restriction sites, although the authors included enzyme sites in amplification primers to mitigate this.

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Integrity signals

Registry

Crossref · 10.1371/journal.pone.0067801

Cites

114 of 114 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Figures

Figure 1 Purification procedure for melanocytes, iridophores, and retinal pigmented epithelium. Zebrafish are grown to the desired time point; shown in (A) is a six day old fish. (B) Fish are dissociated to a single cell suspension; black melanocytes (arrows) and reflective iridophores (arrowheads) are visible as a small percentage of all cells. (C) Cells are placed atop a Percoll density gradient and centrifuged. (D) The resulting cell pellet is resuspended and analyzed by FACS. Shown is a characteristic FACS plot demonstrating the relative positions of melanocyte and iridophore gates (ovals). Sorted iridophores are shown on the upper left of (D) under incident light. Sorted melanocytes are on the lower right using trans-illumination.
Figure 1 Purification procedure for melanocytes, iridophores, and retinal pigmented epithelium. Zebrafish are grown to the desired time point; shown in (A) is a six day old fish. (B) Fish are dissociated to a single cell suspension; black melanocytes (arrows) and reflective iridophores (arrowheads) are visible as a small percentage of all cells. (C) Cells are placed atop a Percoll density gradient and centrifuged. (D) The resulting cell pellet is resuspended and analyzed by FACS. Shown is a characteristic FACS plot demonstrating the relative positions of melanocyte and iridophore gates (ovals). Sorted iridophores are shown on the upper left of (D) under incident light. Sorted melanocytes are on the lower right using trans-illumination.CC BY · PubMed Central
Figure 2 Schematic of cDNA library preparation. PolyA-selected mRNA (in red) is reverse transcribed using a polyT primer tailed with a universal primer (A). See Table S3 for primer sequences. MMLV reverse transcriptase adds cytosines to the 3′ end of the 1st strand cDNA (in black), allowing for template switching and addition of the 3′ universal primer (B). PCR amplification of the library is followed by RsaI and AluI enzymatic digestion of cDNAs (C), followed by the standard Illumina library preparation steps of end-repair, a single adenine addition, Y-adapter ligation (D), PCR enrichment, and size selection (mock gel shown in E with yellow box indicating area of gel removed for DNA extraction), prior to flowcell generation and sequencing.
Figure 2 Schematic of cDNA library preparation. PolyA-selected mRNA (in red) is reverse transcribed using a polyT primer tailed with a universal primer (A). See Table S3 for primer sequences. MMLV reverse transcriptase adds cytosines to the 3′ end of the 1st strand cDNA (in black), allowing for template switching and addition of the 3′ universal primer (B). PCR amplification of the library is followed by RsaI and AluI enzymatic digestion of cDNAs (C), followed by the standard Illumina library preparation steps of end-repair, a single adenine addition, Y-adapter ligation (D), PCR enrichment, and size selection (mock gel shown in E with yellow box indicating area of gel removed for DNA extraction), prior to flowcell generation and sequencing.CC BY · PubMed Central
Figure 3 The guanine synthesis cycle is highly enriched in iridophores. Shown is a model for guanine production based on transcriptome data as given in Table 6. Genes that are statistically enriched compared to melanocytes are shown in bold, those not statistically different are in normal font. The arrow thicknesses correspond to the fold changes in iridophores relative to whole embryos. Chemical structures are from the KEGG Compound database.
Figure 3 The guanine synthesis cycle is highly enriched in iridophores. Shown is a model for guanine production based on transcriptome data as given in Table 6. Genes that are statistically enriched compared to melanocytes are shown in bold, those not statistically different are in normal font. The arrow thicknesses correspond to the fold changes in iridophores relative to whole embryos. Chemical structures are from the KEGG Compound database.CC BY · PubMed Central

Verification

Claims the paper makes

66 Own result · 35 Own interpretation · 18 Own method · 17 Partly supported · 16 Supported · 13 No full text of the sources · 5 Supported so far · 1 Not supported · 1 Couldn’t confirm · 1 Sources not found · 1 Not checked yet · 1 No basis given · accuracy not yet measured

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Show all 122 claims

  • Probably not a substantial claim. 40
  • It may state two separate claims as one. 22
  • The quote only partly states this claim. 3
53 of 53
  • The paper relies on this without support.

    This is the first analysis of the iridophore transcriptome.

    “This is also the first analysis of the iridophore transcriptome.”
    “Furthermore, this is the first characterization of the iridophore transcriptome.”
  • The paper relies on this without support.

    The purification procedure and expression analysis provide the first mRNA sequencing data for multiple purified zebrafish pigment cell types.

    “The purification procedure and expression analysis described here, along with the accompanying transcriptome-wide expression data, provide the first mRNA sequencing data for multiple purified zebrafish pigment cell types, and will be a useful resource for further studies of pigment cell biology.”
  • The paper relies on this without support.

    It is unknown whether markers of neural crest identity persist in iridophores following development, and whether these markers are shared by other neural crest-derived pigment cells, such as melanocytes.

    “However, it is unknown if markers of neural crest identity persist in iridophores following development, and whether these markers are shared by other neural crest-derived pigment cells, such as melanocytes.”
  • The paper relies on this without support.

    It is unknown whether RPE and melanocytes use different pathways of melanin production, or if they are essentially identical.

    “However, it is unknown whether RPE and melanocytes use different pathways of melanin production, or if they are essentially identical.”
  • The paper relies on this without support.

    The percentage of melanocytes, iridophores, and RPE compared to all other cells in the fish is less than 1%.

    “However, the percentage of melanocytes, iridophores, and RPE compared to all other cells in the fish is less than 1%, making cell-specific gene expression analysis from the whole organism difficult.”
  • The paper relies on this without support.

    Genes co-enriched among pigment cell types indicate shared pigment cell functions.

    “We reasoned that genes co-enriched among pigment cell types would indicate shared pigment cell functions.”
  • The paper relies on this without support.

    RPE and iridophores do not share a pigment-type production or developmental origin.

    “Given that the RPE and iridophores do not share a pigment-type production or developmental origin, we expected fewer genes to be co-enriched in these cells, but not expressed by neural-crest melanocytes.”
  • The paper relies on this without support.

    Melanocytes and RPE share the function of producing melanin and melanosomes.

    “Due to their shared function of producing melanin and melanosomes, we expected many genes to be shared between melanocytes and the RPE when compared to iridophores.”
  • The paper relies on this without support.

    mitfa is not required for RPE development in zebrafish.

    “Although not required for RPE development in zebrafish, mitfa is expressed in the RPE at a relatively high level, consistent with the reported ability of mitfa to promote pigmented fate in zebrafish retinas [59].”
  • The paper relies on this without support.

    Melanocytes and iridophores share a common developmental origin from the neural crest.

    “Because of the common developmental origin from the neural crest for melanocytes and iridophores, we speculated that neural crest-specific gene expression would be readily identifiable.”
  • The paper relies on this without support.

    The iridophore transcriptome has not previously been explored.

    “In contrast to melanocytes and RPE, the iridophore transcriptome has not previously been explored.”
  • The paper relies on this without support.

    Iridophores produce a guanine-based pigment, whereas melanocytes and RPE produce melanin.

    “Since iridophore produce a guanine-based pigment, rather than the melanin characteristic of melanocytes and RPE, we expected to find many genes to be specifically enriched in this cell type.”
  • The paper relies on this without support.

    In mammals, the SLC23 gene family has roles in transporting nucleobases, such as guanine, as well as vitamin C.

    “In mammals, the SLC23 gene family has roles in transporting nucleobases, such as guanine, as well as vitamin C.”
  • The paper relies on this without support.

    Iridophores are relatively less-studied than melanocytes and RPE, and aside from requirements for foxd3, ednrb1, and ltk, not much is known about transcriptional regulation of iridophore identity.

    “Iridophores are a relatively less-studied pigment cell than melanocytes and RPE, and aside from the requirements for foxd3, ednrb1, and ltk, not much is known regarding the transcriptional regulation of iridophore identity.”
  • The paper relies on this without support.

    mycl1a is a paralog of the classic oncogenic protein MYC.

    “This gene, mycl1a, is a paralog of the classic oncogenic protein MYC.”
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Metadata

Authors
Higdon, C. W., Mitra, R. D., & Johnson, S. L.
Affiliations
Washington University in St. Louis (US)
Corresponding author
  • Higdon, Charles W.
  • Johnson, Stephen L.
Venue
PLoS ONE
Published
2013-07-09
Volume
8
Issue
7
Pages
e67801
ISSN
1932-6203 (ISSN-L)
OpenAlex
W2144853273
Cited by
125
References
114
Citations by year
2026: 8 · 2025: 8 · 2024: 10 · 2023: 16 · 2022: 5 · 2021: 12 · 2020: 12 · 2019: 11 · 2018: 11 · 2017: 18 · 2016: 4 · 2015: 9 · 2014: 1
FWCI
2.71
Type
journal article
Language
en
Open access
Locations
  • PLoS ONE (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Digital Commons@Becker (Washington University School of Medicine) (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • Figshare (submittedVersion, cc-by)
Funders
  • W. M. Keck Foundation
  • Alvin J. Siteman Cancer Center
  • National Institutes of Health (RO1-GM56988)
  • National Institute of General Medical Sciences (R01GM056988)
  • National Institute of Neurological Disorders and Stroke (R01NS076993)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › melanin and skin pigmentation
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Zebrafish Biomedical Research Applications
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Developmental Biology and Gene Regulation
Keywords
zebrafish, melanocytes, iridophores, retinal pigment epithelium, transcriptome, cell purification, neural crest, purine biosynthesis, phosphoribosylpyrophosphate, melanogenesis, developmental origins
MeSH terms
Animals, Cell Differentiation, Embryo, Nonmammalian, Guanine, Melanocytes, Organ Specificity, Zebrafish, Gene Expression Regulation, Developmental, Gene Expression Profiling, Biosynthetic Pathways, Retinal Pigment Epithelium

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