title: Calaxin drives sperm chemotaxis by Ca²⁺-mediated direct modulation of a dynein motor.
abstract: Sperm chemotaxis occurs widely in animals and plants and plays an important role in the success of fertilization. Several studies have recently demonstrated that Ca(2+) influx through specific Ca(2+) channels is a prerequisite for sperm chemotactic movement. However, the regulator that modulates flagellar movement in response to Ca(2+) is unknown. Here we show that a neuronal calcium sensor, calaxin, directly acts on outer-arm dynein and regulates specific flagellar movement during sperm chemotaxis. Calaxin inhibition resulted in significant loss of sperm chemotactic movement, despite normal increases in intracellular calcium concentration. Using a demembranated sperm model, we demonstrate that calaxin is essential for generation and propagation of Ca(2+)-induced asymmetric flagellar bending. An in vitro motility assay revealed that calaxin directly suppressed the velocity of microtubule sliding by outer-arm dynein at high Ca(2+) concentrations. This study describes the missing link between chemoattractant-mediated Ca(2+) signaling and motor-driven microtubule sliding during sperm chemotaxis.
authors.affiliation: Shimoda Marine Research Center,  University of Tsukuba, Shizuoka 415-0025,  Japan.
authors.forename: Katsutoshi
authors.initials: K
authors.lastname: Mizuno
authors.forename: Kogiku
authors.initials: K
authors.lastname: Shiba
authors.forename: Masahiko
authors.initials: M
authors.lastname: Okai
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Shitaka
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Oiwa
authors.forename: Masaru
authors.initials: M
authors.lastname: Tanokura
authors.forename: Kazuo
authors.initials: K
authors.lastname: Inaba
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000502:physiology; D002219:Carbamates / Q000494:pharmacology; D002633:Chemotaxis / Q000187:drug effects / Q000502:physiology; D002938:Ciona intestinalis / Q000166:cytology / Q000502:physiology; D004398:Dyneins / Q000502:physiology*; D052139:Intracellular Calcium-Sensing Proteins / Q000502:physiology*; D008297:Male; D008870:Microtubules / Q000502:physiology; D008954:Models, Biological; D020409:Molecular Motor Proteins / Q000502:physiology; D010880:Piperidines / Q000494:pharmacology; D013081:Sperm Motility / Q000502:physiology; D013082:Sperm Tail / Q000502:physiology; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology*
chemical_list: D002219:Carbamates; D052139:Intracellular Calcium-Sensing Proteins; D020409:Molecular Motor Proteins; D010880:Piperidines; C072379:repaglinide; D004398:Dyneins