title: Chemotactic response with a constant delay-time mechanism in Ciona spermatozoa revealed by a high time resolution analysis of flagellar motility.
abstract: During their chemotactic swimming toward eggs, sperm cells detect their species-specific chemoattractant and sense concentration gradients by unknown mechanisms. After sensing the attractant, sperm cells commonly demonstrate a series of responses involving different swimming patterns by changing flagellar beats, gradually approaching a swimming path toward the eggs, which is the source of chemoattractants. Shiba et al. observed a rapid increase in intracellular Ca(2+) concentrations in Ciona spermatozoa after sensing chemoattractants; however, the biochemical processes occurring inside the sperm cells are unclear. In the present study, we focused on the timing and sensing mechanism of chemical signal detection in Ciona. One of the most crucial problems to be solved is defining the initial epoch of chemotactic responses. We adopted a high rate of video recording (600 Hz) for detailed analysis of sperm motion and a novel method for detecting subtle signs of beat forms and moving paths of sperm heads. From these analyses, we estimated a virtual sensing point of the attractant before initiation of motility responses and found that the time delay from sensing to motility responses was almost constant. To evaluate the efficiency of this constant delay model, we performed computer simulation of chemotactic behaviors of Ciona spermatozoa.
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Miyashiro
authors.affiliation: Shimoda Marine Research Center, University of Tsukuba, Shizuoka 415-0025, Japan.
authors.forename: Kogiku
authors.initials: K
authors.lastname: Shiba
authors.affiliation: Department of Biological Sciences, Faculty of Science and Engineering, Chuo University, Tokyo 112-8551, Japan.
authors.forename: Tahahiro
authors.initials: T
authors.lastname: Miyashita
authors.affiliation: Department of Advanced Biosciences, Graduate School of Humanities and Sciences, Ochanomizu University, Bunkyo, Tokyo 112-8610, Japan.
authors.forename: Shoji A
authors.initials: SA
authors.lastname: Baba
authors.affiliation: Misaki Marine Biological Station, Graduate School of Science, University of Tokyo, Miura, Kanagawa 238-0225, Japan.
authors.forename: Manabu
authors.initials: M
authors.lastname: Yoshida
authors.affiliation: Department of Biological Sciences, Faculty of Science and Engineering, Chuo University, Tokyo 112-8551, Japan skam@bio.chuo-u.ac.jp.
authors.forename: Shinji
authors.initials: S
authors.lastname: Kamimura
keywords: Ciona intestinalis; Constant delay model; Flagellar motility; Sperm chemotaxis