Cited by 87Zebrafish Biomedical Research Applicationsmelanin and skin pigmentationDevelopmental Biology and Gene Regulation

A defect in the mitochondrial protein Mpv17 underlies the transparent casper zebrafish

Open access
D’Agati, Gianluca, Beltre, Rosanna, Sessa, Anna, Burger, Alexa, Zhou, Yi, Mosimann, Christian, White, Richard M.·2017·Developmental Biology

Abstract

The casper strain of zebrafish is widely used in studies ranging from cancer to neuroscience. casper offers the advantage of relative transparency throughout adulthood, making it particularly useful for in vivo imaging by epifluorescence, confocal, and light sheet microscopy. casper was developed by selective breeding of two previously described recessive pigment mutants: 1) nacre, which harbors an inactivating mutation of the mitfa gene, rendering the fish devoid of pigmented melanocytes; and 2) roy orbison, a mutant with so-far unidentified genetic cause that lacks reflective iridophores. To clarify the molecular nature of the roy orbison mutation, such that it can inform studies using casper, we undertook an effort to positionally clone the roy orbison mutation. We find that roy orbison is caused by an intronic defect in the gene mpv17, encoding an inner mitochondrial membrane protein that has been implicated in human mitochondrial DNA depletion syndrome. The roy orbison mutation is phenotypically and molecularly remarkably similar to another zebrafish iridophore mutant called transparent. Using Cas9-induced crispants and germline mutants with disrupted mpv17 open reading frame, we show in trans-heterozygote embryos that new frameshift alleles of mpv17, roy orbison, and transparent fail to complement each other. Our work provides genetic evidence that both roy orbison and transparent affect the mpv17 locus by a similar if not identical genetic lesion. Identification of mpv17 mutants will allow for further work probing the relationship between mitochondrial function and pigmentation, which has to date received little attention.

AI snapshot

Written from the paper’s full text.

TL;DR

The transparent casper zebrafish strain’s roy orbison mutation is caused by an intronic defect in mpv17, producing aberrant splicing and a likely null allele. Genetic complementation and CRISPR-Cas9 alleles show roy orbison and transparent are allelic to mpv17 and to each other.

Key findings

  • roy orbison mutants carry a 19 bp deletion in mpv17 mRNA causing aberrant splicing between exons 2 and 3, frameshift, and early stop; the genomic lesion is intronic and intron 2–3 could not be amplified.
  • mpv17 mRNA injection rescued eye iridophores in 16/20 roy embryos at 4 dpf; ATG morpholino caused complete iridophore loss in 72% (n=48/67) and moderate loss in 16% (n=11/67) of injected embryos, versus 89% normal uninjected AB embryos (p<0.05).
  • CRISPR-Cas9 mpv17 crispants showed iridophore loss in an average of 77% (n=172/223) of F0 embryos; germline mpv17 frameshift alleles failed to complement roya9 and trab6, and trans-heterozygous mpv17Δ1/Δ5 adults lacked eye iridophores and had melanocyte stripe defects.
  • Array CGH showed skin:kidney mtDNA log2 fold-change of 0.733±0.46 SEM in AB versus −0.742±0.19 in roy orbison (p<0.05), consistent with relative mtDNA decrease in roy skin.

Methods

  • Positional cloning used roy outcrosses to WIK, a 1672-fish mapping panel, linkage group 20 SNP markers, candidate gene qRT-PCR, and cDNA cloning/Sanger sequencing.
  • Functional validation used mpv17 mRNA rescue, ATG morpholino knockdown, CRISPR-Cas9 RNP injections targeting mpv17 exon 2 or exon 3, germline allele recovery, and complementation crosses with roya9 and trab6.
  • mtDNA content was assessed by array CGH on skin and kidney from 3 AB and 3 roy adults; iridophore counts and array CGH data were compared with unpaired t-tests at p<0.05.

Limitations

  • The paper states it could not isolate specific skin cell types such as iridophores, so the lower mtDNA signal in roy skin may simply reflect absent iridophores rather than intrinsic mtDNA depletion.
  • The paper notes that F0 mpv17 crispants recover iridophores with age, likely because wildtype or hypomorphic clones replace mutant clones in mosaics, a caveat of somatic mutant analysis.
  • The paper states the intron 2–3 deletion could not be properly charted and it remains unclear whether roya9 and trab6 arose independently or from the same founder mutation.
  • Evident from the text: array CGH used only 3 fish per genotype, and morpholino-injected embryos showed heart defects that may be nonspecific toxicity.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1016/j.ydbio.2017.07.017

Cites

22 of 22 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

8 of 10 cited sources checked · 5 supported · 0 flagged · accuracy not yet measured

  • Interpretationown data

    Both roy orbison and transparent affect the mpv17 locus by a similar if not identical genetic lesion.

    “Our work provides genetic evidence that both roy orbison and transparent affect the mpv17 locus by a similar if not identical genetic lesion.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Krauss et al., 2013 source

      The Results section (‘transparent encodes the mitochondrial protein Mpv17’; page unavailable) identifies a deletion in mpv17 that causes the transparent phenotype. Our copy does not identify a genetic lesion in roy orbison or compare it with transparent’s, so the claim that the two lesions are similar or identical is unsupported by this source. (LLM, conf=0.86)

      Experimental — accuracy not yet measured
  • Premisecitation

    There are significant inter-species differences in the consequences of mpv17 mutation.

    “As recently reviewed by Löllgen and Weiher (Löllgen and Weiher, 2015), there is significant inter-species differences in the consequences of mpv17 mutation.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites Löllgen and Weiher, 2015 source
  • Premisecitation

    Zebrafish mpv17 localizes to the mitochondria, similar to the human and mouse protein.

    “Krauss, et al, also recently noted that zebrafish mpv17 also localizes to the mitochondria, similar the the human and mouse protein.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Krauss et al., 2013 source
  • Premisecitation

    mpv17 is highly enriched in iridophores compared to other pigment cells such as melanocytes.

    “Higdon and Johnson showed by RNA-seq that mpv17 is highly enriched in iridophores compared to other pigment cells such as melanocytes (Higdon et al., 2013).”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Higdon et al., 2013 source

      The Introduction describes mRNA sequencing of zebrafish pigment cells, and the Results and Discussion section on iridophore gene enrichment reports genes enriched relative to melanocytes. Neither the supplied passages nor searches for mpv17 and its proposed enrichment found a result for that gene, so our copy does not establish the specific comparison claimed. (LLM, conf=0.72)

      Experimental — accuracy not yet measured
  • Findingown data

    The roy orbison mutation is phenotypically and molecularly remarkably similar to the zebrafish iridophore mutant transparent.

    “The roy orbison mutation is phenotypically and molecularly remarkably similar to another zebrafish iridophore mutant called transparent.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Krauss et al., 2013 source

      The Introduction describes transparent as a zebrafish mutant with strongly reduced iridophore pigmentation, and the Results identify a deletion in mpv17. Our copy does not describe the roy orbison mutation or establish that the two mutants are phenotypically and molecularly similar (searched: “roy orbison” and “roy mpv17 iridophore mutant”). (LLM, conf=0.81)

      Experimental — accuracy not yet measured
  • Classified as probably not a substantial claim. 7
  • May combine two claims. 18
  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    The kidney of the casper strain appears histologically normal, in contrast to the mouse mutant for Mpv17.

    “Furthermore, We previously noted that the kidney of the casper strain appears histologically normal, in contrast to the mouse mutant for Mpv17 (Viscomi et al., 2009).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites Viscomi et al., 2009 source
  • May combine two claims.

    Premisecitation

    mpv17 encodes an inner mitochondrial membrane protein that has been implicated in human mitochondrial DNA depletion syndrome.

    “Here, we provide sequencing and genetic evidence that the phenotype of roy is due to a defect in the mitochondrial inner membrane protein mpv17, which has previously been associated with the mitochondrial DNA depletion syndrome in mammals (Löllgen and Weiher, 2015).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites Löllgen and Weiher, 2015 source
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The transparent mutant was linked to the identical defect in the mpv17 mRNA.

    “Importantly, a recent publication linked the highly similar mutant tra to the identical defect in the mpv17 mRNA (Krauss et al., 2013), suggesting these two mutants are caused by similar or even the same lesion.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites Krauss et al., 2013 source
  • May combine two claims.

    Findingown data

    Fine-resolution mapping between markers z13672 and z28453 led to few recombinants between markers zp6 and zp10, with only 8 genes in that interval.

    “For the fine-resolution mapping between markers z13672 and z28453, custom designed PCR primers based on the Zv9 zebrafish build were used, which led to few recombinants between markers zp6 and zp10, with only 8 genes in that interval.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    Cas9-induced disruption of the mpv17 ORF in F0 crispants causes iridophore loss; an average of 77% (172/223) of mpv17ccB crispants featured iridophore loss.

    “Embryos injected with the mpv17ccB sgRNA displayed a specific, strong reduction of iridophores predominantly in the eye and trunk region (Figure 4B,C); an average of 77% (n=172/223) of CRISPR-injected F0 embryos (so-called crispants) consistently featured iridophore loss (Figure 4D).”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    roya9 and trab6 neither complement each other nor mpv17 frameshift alleles.

    “In both crosses, genotype-confirmed offspring harboring frameshift alleles arising from mpv17ccB and mpv17ccC presented a strong iridophore reduction in the eye, trunk, and swimbladder area, revealing non-complementation of roya9 and trab6 by de novo mutants affecting the mpv17 ORF.”
    • Also stated in: § roya9 and transparentb6 neither complement each other nor mpv17 frameshift alleles · plain
      “We also crossed roya9/a9;nacw2/w2 to trab6/b6;nacw2/w2 and observed complete penetrance of the roy orbison and nacre phenotypes, resulting in embryos that are indistinguishable from casper.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    The roy orbison phenotype segregates in a Mendelian ratio, with ~25% of offspring having severely reduced or absent iridophores.

    “This revealed Mendelian segregation of the roy orbison phenotype, with ~25% of offspring having severely reduced or absent iridophores.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    In contrast to humans or mice with mpv17 mutations, no gross defects in liver, kidney or muscle were seen in the fish, with the majority of defects confined to the skin.

    “In contrast to humans or even mice with mutations in mpv17, we see no gross defects in liver, kidney or muscle in our fish, with the majority of defects confined to the skin.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    Injecting functional mpv17 mRNA into homozygous roy embryos rescues the mutant eye iridophore phenotype; 16/20 surviving fish had fully rescued eye iridophores.

    “These observations suggest that supplementing homozygous roy embryos with functional mpv17-encoding mRNA rescues the mutant phenotype.”
    • Also stated in: § mpv17 mRNA rescues the roy orbison phenotype · plain
      “Of the 20 fish that survived to 4 dpf, 16/20 had fully rescued eye iridophores (Figure 3A).”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    In roy orbison, the mtDNA skin:kidney ratio was −0.742±0.19, opposite to AB, p<0.05.

    “In contrast, in roy orbison, the exact opposite was found, where the mtDNA skin:kidney ratio was −0.742+/−0.19 (p<0.05, AB vs. roy orbison, unpaired t-test).”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingown data

    F0 mpv17 crispants recover iridophores over time and are virtually indistinguishable from wildtype controls at 3 months of age.

    “While strikingly visible at early stages, we observed a gradual recovery in iridophores over time and crispants were virtually indistinguishable from wildtype controls at 3 months of age (data not shown).”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingown data

    Trans-heterozygous mpv17Δ1/Δ5 adults are completely devoid of iridophores in the eye and display nearly complete iridophore loss along the body axis.

    “Compared to wildtype, 3 month old mpv17Δ1/Δ5 were completely devoid of iridophores in the eye and also displayed a nearly complete iridophore loss along the body axis.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingreasoning

    The casper strain maintains excellent health and fecundity throughout its lifespan.

    “Nonetheless, we find that in general the casper strain maintains excellent health and fecundity throughout its lifespan.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingown data

    ATG morpholino knockdown of mpv17 in wildtype embryos causes iridophore loss: 87% showed complete or moderate loss, 12% normal, versus 89% normal uninjected, p<0.05.

    “We examined the injected embryos at 4–7 dpf and noted a range of phenotypes, with 87% of embryos showing either complete (72%, n=48/67) or moderate (16%, n=11/67) loss of iridophores. Only 12% of the injected fish had normal appearing iridophores, in contrast to 89% of the uninjected AB embryos (p<0.05, uninjected vs. injected embryos, paired t-test).”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim.

    Interpretationreasoning

    Iridophore recovery in F0 crispants is likely due to the mosaic nature of the transient mutagenesis assay.

    “We suspect that iridophore recovery is possible due to the mosaic nature of our transient mutagenesis assay.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisenone given

    In humans, the primary defect of mpv17 mutation seems to occur in the liver, with severe loss of mtDNA and hepatocerebral disease.

    “In humans, the primary defect seems to occur in the liver, with a severe loss of mtDNA and the clinical syndrome most severe with hepatocerebral disease, often occurring in young children.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    nacre harbors an inactivating mutation of the mitfa gene, rendering the fish devoid of pigmented melanocytes.

    “For example, the zebrafish nacre (nac) mutant harbors an an inactivating mutation in the mitfa gene and are devoid of nearly all embryonic and adult melanophores (Lister et al., 1999), emphasizing the key role of this transcription factor as a master regulator of this cell type.”
    • Also stated in: § DISCUSSION · boosted
      “Whereas nac is well-known to be due to an inactivating mutation in mitfa resulting in loss of pigmented melanocytes (Lister et al., 1999), the nature of the roy mutation has remained obscure.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Lister et al., 1999 source
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given

    The mouse mpv17 mutant was originally noted for severe renal disease resembling focal segmental glomerulosclerosis.

    “In contrast, the mouse mutant, which has been extensively analyzed, was originally noted for its severe renal disease resembling focal segmental glomerulosclerosis.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    The mouse liver shows a large decrease in mtDNA content, with only 4% of WT; kidney is less affected with 60% of WT, and glomerular podocytes are severely affected while renal tubules are relatively normal.

    “Interestingly, the liver in the mouse shows the expected large decrease in mtDNA content, with only 4% of the content compared to WT. In contrast, the kidney is less affected in this regard, with overall 60% of the levels seen in WT, but even within this tissue the effect is heterogeneous, with the glomerular podocytes severely affected while the renal tubules were relatively normal(Spinazzola et”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Spinazzola et al., 2006 source
  • May combine two claims.

    Interpretationreasoning

    The 19 bp deletion leads to a frameshift and early stop codon that likely yields a null for the mpv17 protein.

    “This leads to a frameshift and early stop codon that likely yields a null for the protein.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationown data

    roy orbison and transparent form a complementation group and are allelic to mpv17.

    “Taken together, our complementation analysis confirms that the zebrafish mutants roy orbison and transparent form a complementation group and are allelic to mpv17, as further confirmed by our independently derived generated frameshift alleles.”
    Quote in the paperSubstantial claim
21 of 21
  • The authors state this as an assumption.

    The underlying genomic defect causing the roy mpv17 splicing defect occurs in the intron between exons 2 and 3.

    “We therefore assumed that the underlying genomic defect occurs in the intron between exons 2 and 3, but we repeatedly failed to amplify the genomic DNA from intron 2–3, suggesting there is a deletion in this intron that leads to aberrant splicing and subsequent early stop of the mRNA.”
1 of 1

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Eight candidate genes claimed, but only seven listed

    Minor

    The candidate-gene list contains seven names, not eight.

1 of 1

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Authors
D’Agati, G., Beltre, R., Sessa, A., Burger, A., Zhou, Y., Mosimann, C., & White, R. M.
Affiliations
  • Boston Children's Hospital (US)
  • University of Zurich (CH)
  • Memorial Sloan Kettering Cancer Center (US)
Corresponding author
  • Mosimann, Christian
  • White, Richard M.
Venue
Developmental Biology
Publisher
Elsevier BV
Published
2017-10
Volume
430
Issue
1
Pages
11-17
ISSN
0012-1606 (ISSN-L)
OpenAlex
W2739911723
Cited by
87
References
22
Citations by year
2026: 8 · 2025: 10 · 2024: 9 · 2023: 10 · 2022: 12 · 2021: 15 · 2020: 10 · 2019: 8 · 2018: 5
FWCI
3.36
Type
journal article
Language
en
Open access
Locations
  • Developmental Biology (publishedVersion)
  • PubMed (publishedVersion)
  • Europe PMC (PubMed Central) (acceptedVersion)
  • PubMed Central (acceptedVersion)
  • Zurich Open Repository and Archive (University of Zurich) (submittedVersion)
Funders
  • Canton of Zürich and the Foundation for Research in Science and the Humanities
  • Swiss National Science Foundation (SNSF) professorship (PP00P3_139093)
  • European Commission (CIG PCIG14-GA-2013-631984)
  • Translational Cancer Research
  • Swiss Bridge Foundation
  • CanDoc Forschungskredit
  • NIH Director's New Innovator Award (DP2CA186572)
  • Mentored Clinical Scientist Research Career Development Award (K08AR055368)
  • Melanoma Research Alliance Young Investigator Award
  • Memorial Sloan Kettering Cancer Center
  • The Harry J. Lloyd Foundation
  • Consano
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Zebrafish Biomedical Research Applications
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › melanin and skin pigmentation
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Developmental Biology and Gene Regulation
Keywords
MPV17, iridophores, mitochondrial proteins, positional cloning, frameshift mutation, complementation, mitochondrial DNA depletion syndrome, melanocytes, mitfa, in vivo imaging
MeSH terms
Alleles, Animals, Base Sequence, Chromosome Mapping, DNA, Mitochondrial, Membrane Proteins, Mutation, Phenotype, Pigmentation, RNA, Messenger, Zebrafish, Mutagenesis, Base Pairing, Mitochondrial Proteins, Zebrafish Proteins, Gene Knockdown Techniques, Genetic Loci, Morpholinos, CRISPR-Cas Systems

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