A novel neuronal calcium sensor family protein, calaxin, is a potential Ca2+-dependent regulator for the outer arm dynein of metazoan cilia and flagella

Authors

  • Katsutoshi Mizuno,

    1. Shimoda Marine Research Center, University of Tsukuba, Shimoda 5-10-1, Shizuoka 415-0025, Japan
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    • These authors contributed equally to this work.

  • Potturi Padma,

    1. Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai 980-8578, Japan
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    • These authors contributed equally to this work.

  • Aru Konno,

    1. Shimoda Marine Research Center, University of Tsukuba, Shimoda 5-10-1, Shizuoka 415-0025, Japan
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  • Yuhkoh Satouh,

    1. Shimoda Marine Research Center, University of Tsukuba, Shimoda 5-10-1, Shizuoka 415-0025, Japan
    2. Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai 980-8578, Japan
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  • Kazuo Ogawa,

    1. Center for Radioisotope Facilities, Okazaki Research Facilities, National Institute of Natural Sciences, Okazaki 444-8787, Japan
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  • Kazuo Inaba

    Corresponding author
    1. Shimoda Marine Research Center, University of Tsukuba, Shimoda 5-10-1, Shizuoka 415-0025, Japan
    2. Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai 980-8578, Japan
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    • These authors contributed equally to this work.


  • The nucleotide sequence data reported for Ciona intestinalis calaxin will appear in the DDBJ, EMBL, GenBank® and GSDB Nucleotide Sequence Databases under the accession number AB079059.

(email inaba@kurofune.shimoda.tsukuba.ac.jp).

Abstract

Background information. Spermatozoa show several changes in flagellar waveform, such as upon fertilization. Ca2+ has been shown to play critical roles in modulating the waveforms of sperm flagella. However, a Ca2+-binding protein in sperm flagella that regulates axonemal dyneins has not been fully characterized.

Results. We identified a novel neuronal calcium sensor family protein, named calaxin (Ca2+-binding axonemal protein), in sperm flagella of the ascidian Ciona intestinalis. Calaxin has three EF-hand Ca2+-binding motifs, and its orthologues are present in metazoan species, but not in yeast, green algae or plant. Immunolocalization revealed that calaxin is localized near the outer arm of the sperm flagellar axonemes. Moreover, it is distributed in adult tissues bearing epithelial cilia. An in vitro binding experiment indicated that calaxin binds to outer arm dynein. A cross-linking experiment showed that calaxin binds to β-tubulin in situ. Overlay experiments further indicated that calaxin binds the β-dynein heavy chain of outer arm dynein in the presence of Ca2+.

Conclusions. These results suggest that calaxin is a potential Ca2+-dependent modulator of outer arm dynein in metazoan cilia and flagella.

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