Calcium signaling modulates the dynamics of cilia and flagella
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ORIGINAL ARTICLE
Calcium signaling modulates the dynamics of cilia and flagella M. V. Satarić1 · S. Zdravković2 · T. Nemeš3 · B. M. Satarić3 Received: 12 September 2020 / Accepted: 12 October 2020 © European Biophysical Societies’ Association 2020
Abstract To adapt to changing environments cells must signal and signaling requires messengers whose concentration varies with time in space. We here consider the messenger role of calcium ions implicated in regulation of the wave-like bending dynamics of cilia and flagella. The emphasis is on microtubules as polyelectrolytes serving as transmission lines for the flow of Ca2+ signals in the axoneme. This signaling is superimposed with a geometric clutch mechanism for the regulation of flagella bending dynamics and our modeling produces results in agreement with experimental data. Keywords Cilium · Flagellum · Microtubule · Dynein motors · Calcium signaling
Introduction Cilia and flagella are long, thin active organelles whose oscillatory bending waves serve to propel cells or move fluid. When many cilia beat in synchrony, they can move fluid along the surface of cells. Examples of cilia responsible for fluid flow are the modal cilia involved in the breaking of left–right symmetry in the development of vertebrate embryos (Nonaka et al. 1998). Exceptionally important are the cilia in the mammalian lung trachea responsible for the flow of mucus (Sleigh et al. 1988). An example of an organism with two cilia is the unicellular algae Chlamydomonas reinhardati, which is the focus of this article. Paramecium has as many as hundreds of cilia to act as micro-swimmers propelling it through water. Cells with one motile flagellum include the sperm cells of the sea urchin, bull and anopheles as well as human sperm. In the core of cilium and flagellum sits a motile internal cytoskeletal cylindrical structure called the axoneme (Nicastro et al. 2006). The axoneme consists of a regular arrangement of nine microtubule doublets associated with other structural elements including the radial spokes, nexin * T. Nemeš [email protected] 1
Serbian Academy of Science and Arts, Belgrade, Serbia
2
Vinča Institute for Nuclear Sciences, University of Belgrade, Belgrade, Serbia
3
Faculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia
linkers, a central pair of microtubules and axonemal dynein motor proteins, see Fig. 1a, b (Nicastro et al. 2006). Microtubules are thin long hollow cylinders containing 13 parallel protofilaments polymerized from alpha–beta tubulin heterodimers. The diameter of the microtubule is 25 nm. Every microtubule doublet is composed of one A-microtubule and one B-microtubule. The A-microtubule contains a standard 13 protofilaments while the B-microtubule has only 10 protofilaments and is tightly fused with the A-microtubule, Fig. 1c. The doublets are parallel to each other with inter spacing of about 30 nm which is close to the diameter of the microtubule. Radial spokes and nexin linkers have a role in keeping the diameter of the axoneme
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