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INI-RIMS joint seminar: Regulatory mechanism for sperm chemotaxis and flagellar motility

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MMV - Mathematics of movement: an interdisciplinary approach to mutual challenges in animal ecology and cell biology

Eukaryotic flagella and cilia are extremely important organelles in cell motility and signal reception, such as sperm motility and control of water flow in the body, and their structure and function are highly conserved throughout evolution. I aim to elucidate the molecular and cellular biology of the regulation of sperm flagellar motility by using the original experimental and analytical systems for the functional analysis of fine and fast-moving flagella and cilia. I use the ascidian, Ciona sperm as experimental animal. Ciona spermatozoa have long been used for the analysis of sperm and flagellar motility due to their advantages in terms of ease of sample handling, simplicity of morphology, internal structure and motility [1]. Egg-derived sperm attractants have also been identified, and the dramatic changes in swimming direction and flagellar waveform during sperm chemotaxis can be recorded under a microscope [2]. Sperm chemotactic behavior is characterized by a change of direction when sperm swim away the attractant source. This feature is widely conserved among organisms. The sperm flagellar wave generates propulsion by the alternating propagation of two bends from the base to tip. If the curvature of two bends is equal, the sperm swim straight ahead. On the other hand, if the curvature of one bend is larger than another bend, the sperm perform a circular motion. Analysis of the changes in the flagellar waveforms of Cionasperm during chemotaxis revealed that the difference between the two bends curvature increases significantly when the sperm swim away from the attractant source, leading to a turn movement that changes direction, and then the curvatre of the two bends becomes equal and the sperm swim straight towards the attractant source. The series of changes in the waveforms are repeated and finally the sperm reaches the attractant source. Realtime calcium imaging using fluorescent calcium indicator also showed that a transient increase in the concentration of calcium ions in the flagellum triggers the waveform change [3]. Calcium ions are important second messengers in the signaling pathway of attractant reception and directly regulate the molecular motor dynein that drives flagellar movement.   Our goal is understanding how sperm sense the attractant concentration gradient, drive calcium signaling, and regulate the flagellar motor. In this talk, I will introduce our biological experiments and studies to reveal the function of the calcium-binding protein calaxin, which directly interact dynein activity, and the role of ion channels in chemoattractant sensing signaling in flagellar waveform regulation [4-5]. I would also like to discuss our recent challenge to understand the skillful behavioral strategies of swimming single cells through “Ethological dynamics in diorama environments” [6]. References: [1] Brokaw, J Cell Biol. 114(6):1201-15 (1991)  [2] Yoshida et al., Proc Natl Acad Sci U S A . 99(23):14831-6 (2002)  [3] Shiba et al., Proc Natl Acad Sci U S A . 105(49):19312-7 (2008)  [4] Shiba et al., Int J Mol Sci. 23(3):1648 (2022)  [5] Shiba et al., Front Cell Dev Biol. 11:1136404 (2023)  [6]

This talk is part of the Isaac Newton Institute Seminar Series series.

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