Testing the ion-current model for flagellar length sensing and IFT regulation

  1. Hiroaki Ishikawa
  2. Jeremy Moore
  3. Dennis R Diener
  4. Markus Delling
  5. Wallace F Marshall  Is a corresponding author
  1. University of California, San Francisco, United States
  2. Kenyon College, United States
  3. Max Planck Institute of Molecular Cell Biology and Genetics, Germany

Abstract

Eukaryotic cilia and flagella are microtubule-based organelles whose relatively simple shape makes them ideal for investigating the fundamental question of organelle size regulation. Most of the flagellar materials are transported from the cell body via an active transport process called intraflagellar transport (IFT). The rate of IFT entry into flagella, known as IFT injection, has been shown to negatively correlate with flagellar length. However, it remains unknown how the cell measures the length of its flagella and controls IFT injection. One of the most-discussed theoretical models for length sensing to control IFT is the ion-current model, which posits that there is a uniform distribution of Ca2+ channels along the flagellum and that the Ca2+ current from the flagellum into the cell body increases linearly with flagellar length. In this model, the cell uses the Ca2+ current to negatively regulate IFT injection. The recent discovery that IFT entry into flagella is regulated by the phosphorylation of kinesin through a calcium-dependent protein kinase has provided further impetus for the ion-current model. To test this model, we measured and manipulated the levels of Ca2+ inside of Chlamydomonas flagella and quantified IFT injection. Although the concentration of Ca2+ inside of flagella was weakly correlated with the length of flagella, we found that IFT injection was reduced in calcium-deficient flagella, rather than increased as the model predicted, and that variation in IFT injection was uncorrelated with the occurrence of flagellar Ca2+ spikes. Thus, Ca2+ does not appear to function as a negative regulator of IFT injection, hence it cannot form the basis of a stable length control system.

Data availability

Modelling code has been uploaded to Github under repository https://github.com/ishikawaUCSF/temp and a link to the repository is provided in Materials and Methods

Article and author information

Author details

  1. Hiroaki Ishikawa

    Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-3984-3657
  2. Jeremy Moore

    Department of Biology, Kenyon College, Gambier, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Dennis R Diener

    Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
    Competing interests
    The authors declare that no competing interests exist.
  4. Markus Delling

    Department of Physiology, University of California, San Francisco, San Francisco, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-9556-2097
  5. Wallace F Marshall

    Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
    For correspondence
    wallace.marshall@ucsf.edu
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-8467-5763

Funding

National Institutes of Health (R35GM130327)

  • Wallace F Marshall

National Institutes of Health (R01GM130908)

  • Markus Delling

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Lotte B Pedersen, University of Copenhagen, Denmark

Publication history

  1. Received: August 22, 2022
  2. Accepted: January 12, 2023
  3. Accepted Manuscript published: January 13, 2023 (version 1)

Copyright

© 2023, Ishikawa et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Hiroaki Ishikawa
  2. Jeremy Moore
  3. Dennis R Diener
  4. Markus Delling
  5. Wallace F Marshall
(2023)
Testing the ion-current model for flagellar length sensing and IFT regulation
eLife 12:e82901.
https://doi.org/10.7554/eLife.82901

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