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The rate of change in Ca2+ concentration controls sperm chemotaxis

During chemotaxis and phototaxis, sperm, algae, marine zooplankton, and other microswimmers move on helical paths or drifting circles by rhythmically bending cell protrusions called motile cilia or flagella

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Authors:
Luis Alvarez, Luru Dai, Benjamin M. Friedrich, Nachiket D. Kashikar, Ingo Gregor, René Pascal, U. Benjamin Kaupp

Affiliations:
Department of Molecular Sensory Systems, Center of Advanced European Studies and Research (caesar), 53175 Bonn, Germany
National Center for Nanoscience and Technology, Beijing 100190, China
Department of Materials and Interfaces, Weizmann Institute of Science, 76100 Rehovot, Israel
Third Institute of Physics, Faculty of Physics, Georg-August University, 37077 Göttingen, Germany

Abstract:
During chemotaxis and phototaxis, sperm, algae, marine zooplankton, and other microswimmers move on helical paths or drifting circles by rhythmically bending cell protrusions called motile cilia or flagella. Sperm of marine invertebrates navigate in a chemoattractant gradient by adjusting the flagellar waveform and, thereby, the swimming path. The waveform is periodically modulated by Ca2+ oscillations. How Ca2+ signals elicit steering responses and shape the path is unknown. We unveil the signal transfer between the changes in intracellular Ca2+ concentration ([Ca2+]i) and path curvature (κ). We show that κ is modulated by the time derivative d[Ca2+]i/dt rather than the absolute [Ca2+]i. Furthermore, simulation of swimming paths using various Ca2+ waveforms reproduces the wealth of swimming paths observed for sperm of marine invertebrates. We propose a cellular mechanism for a chemical differentiator that computes a time derivative. The cytoskeleton of cilia, the axoneme, is highly conserved. Thus, motile ciliated cells in general might use a similar cellular computation to translate changes of [Ca2+]i into motion.

Full article

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