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FAP20 is an inner junction protein of doublet microtubules essential for both the planar asymmetrical waveform and stability of flagella in Chlamydomonas

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Yanagisawa, Haru-aki, Mathis, Garrison, Oda, Toshiyuki, Hirono, Masafumi, Richey, Elizabeth A., Ishikawa, Hiroaki, Marshall, Wallace F., Kikkawa, Masahide +1 more·2014·Molecular Biology of the Cell
DOI 10.1091/mbc.e13-08-0464PMC PMC4004596
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Abstract

The axoneme—the conserved core of eukaryotic cilia and flagella—contains highly specialized doublet microtubules (DMTs). A long-standing question is what protein(s) compose the junctions between two tubules in DMT. Here we identify a highly conserved flagellar-associated protein (FAP), FAP20, as an inner junction (IJ) component. The flagella of Chlamydomonas FAP20 mutants have normal length but beat with an abnormal symmetrical three-dimensional pattern. In addition, the mutant axonemes are liable to disintegrate during beating, implying that interdoublet connections may be weakened. Conventional electron microscopy shows that the mutant axonemes lack the IJ, and cryo–electron tomography combined with a structural labeling method reveals that the labeled FAP20 localizes at the IJ. The mutant axonemes also lack doublet-specific beak structures, which are localized in the proximal portion of the axoneme and may be involved in planar asymmetric flagellar bending. FAP20 itself, however, may not be a beak component, because uniform localization of FAP20 along the entire length of all nine DMTs is inconsistent with the beak's localization. FAP20 is the first confirmed component of the IJ. Our data also suggest that the IJ is important for both stabilizing the axoneme and scaffolding intra–B-tubular substructures required for a planar asymmetrical waveform.

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  • CFAP20 regulates ciliary movement (waveform) in Paramecium and Chlamydomonas.

    “CFAP20 is a ciliopathy candidate known to modulate motile cilia in unicellular eukaryotes.”

    From The inner junction protein CFAP20 functions in motile and non-motile cilia and is critical for vision (2022) · cites this paper as [16]

    The Results report abnormal flagellar waveform in Chlamydomonas FAP20 mutants and describe altered waveform in FAP20-depleted Paramecium; the Discussion also reports symmetrical beating in both. The Introduction discusses diseases associated with ciliary defects, but our copy does not identify FAP20 itself as a ciliopathy candidate. No page numbers were available in our copy. (LLM, conf=0.84)

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  • In Chlamydomonas, loss of either CFAP20 or PACRG results in a similar dysregulation of ciliary motility.

    “In Chlamydomonas, loss of either protein (CFAP20/PACRG) results in a similar dysregulation of ciliary motility16,17,75.”

    From The inner junction protein CFAP20 functions in motile and non-motile cilia and is critical for vision (2022) · cites this paper as [16]

    The Results section, “FAP20 is essential for establishing the asymmetrical waveform and beating plane” (page unavailable), reports abnormal beating and swimming in Chlamydomonas lacking FAP20. Figure 5’s caption reports reduced PACRG in FAP20-mutant axonemes, but our copy does not report motility after loss of PACRG or establish that the two losses cause similar defects. (LLM, conf=0.86)

    Experimental — accuracy not yet measured

  • Recent studies position CFAP20 specifically as a core inner junction protein.

    “Recent studies position CFAP20 specifically as a core inner junction protein16,19,20 (Fig. 1b).”

    From The inner junction protein CFAP20 functions in motile and non-motile cilia and is critical for vision (2022) · cites this paper as [16]

  • A rare form of recessive inherited retinal dystrophy is attributed to variants in CFAP20.

    “Here, we attribute a rare form of recessive inherited retinal dystrophy (IRD; a classic non-motile ciliopathy10,65,66) to variants in CFAP20, which encodes a remarkably conserved protein with well-established roles in motile cilia from diverse organisms15–18.”

    From The inner junction protein CFAP20 functions in motile and non-motile cilia and is critical for vision (2022) · cites this paper as [16]

  • Transient knockdown of cfap20 disrupts zebrafish left-right organiser cilia, causes cardiac situs defects, and produces body-axis curvature defects.

    “Yanagisawa et al. also demonstrated that transient knockdown of cfap20 disrupts zebrafish left-right organiser cilia, causes cardiac situs defects, and produces body-axis curvature defects16.”

    From The inner junction protein CFAP20 functions in motile and non-motile cilia and is critical for vision (2022) · cites this paper as [16]

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Authors
Yanagisawa, H.-A., Mathis, G., Oda, T., Hirono, M., Richey, E. A., Ishikawa, H., Marshall, W. F., Kikkawa, M., & Qin, H.
Affiliations
  • Department of Cell Biology and Anatomy, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
  • Texas A&M University (US)
  • The University of Tokyo (JP)
  • University of California, San Francisco (US)
Corresponding author
Qin, Hongmin
ORCID
Venue
Molecular Biology of the Cell
Publisher
American Society for Cell Biology (ASCB)
Published
2014-05
Volume
25
Issue
9
Pages
1472-1483
ISSN
  • 1059-1524 (ISSN-L)
  • 1939-4586
DOI
10.1091/mbc.e13-08-0464
PMC
PMC4004596
OpenAlex
W2012973861
Cited by
89
References
67
Citations by year
2026: 6 · 2025: 9 · 2024: 10 · 2023: 15 · 2022: 5 · 2021: 6 · 2020: 8 · 2019: 10 · 2018: 5 · 2017: 6 · 2016: 4 · 2015: 2 · 2014: 3
FWCI
3.28
Type
journal article
Language
en
Open access
Licence
cc-by-nc-sa
Locations
  • Molecular Biology of the Cell (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by-nc-sa)
  • PubMed Central (publishedVersion, cc-by-nc-sa)
  • PubMed (publishedVersion)
  • eScholarship (California Digital Library) (submittedVersion)
Funders
  • University of Minnesota
  • Japan Society for the Promotion of Science (24370079)
  • National Institute of General Medical Sciences (R01GM097017)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Genetic and Kidney Cyst Diseases
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Microtubule and mitosis dynamics
  • Health Sciences › Medicine › Pulmonary and Respiratory Medicine › Cystic Fibrosis Research Advances
Keywords
doublet microtubules, axoneme, flagella, Chlamydomonas, cryo-electron tomography
MeSH terms
Animals, Flagella, Microtubules, Plant Proteins, Zebrafish, Chlamydomonas reinhardtii, Protein Transport, Axoneme, Protein Stability

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