Press Releases
Apr. 1, 2011

How sea urchin sperm avoid obstacles: The mechanosensory response of sperm and its control by calcium

Presenter
  • Chikako Shingyoji (Department of Biological Sciences, Graduate School of Science, University of Tokyo)

Abstract

Sperm of sea urchin, propelled by their flagellar movement, swim toward the egg. What happens when they encounter an obstacle such as another sperm? We found that collision of the sperm head against the obstacle induces a series of flagellar response resulting in the sperm's avoidance of the obstacle by swimming away from it. This response depends on the dynamic control of the movement of calcium ions through the sperm's cell membrane. In sea water containing 10 mM Ca2+, the sperm swim in circular paths near the glass surface of the experimental chamber. When a mechanical stimulus is applied to the sperm head with a glass microstylus, the sperm show a series of flagellar responses, consisting of a stoppage of beating (quiescence) and recovery of swimming in a straight path, followed by swimming in a circular path again; as the result the sperm avoid the obstacle. Ca2+-imaging by using a Ca2+-indicator Fluo-4 has shown that the intracellular Ca2+ is high in the quiescence and gradually decreases after that. The effects of blockers and antibodies against candidate membrane proteins have revealed that the Ca2+ influx is induced by Ca2+ channels and the Ca2+ efflux is induced by organized functioning of several Ca2+-efflux proteins. The results show that the Ca2+-dependent mechanosensory behaviour of the sea urchin sperm is the basis of their avoiding response.

Paper information

Yuka Kambara1, Kogiku Shiba2, Manabu Yoshida2, Chihiro Sato3, Ken Kitajima3 and Chikako Shingyoji1

1Department of Biological Sciences, Graduate School of Science, University of Tokyo; 2Misaki Marine Biological Station, Graduate School of Science, University of Tokyo; 3Bioscience and Biotechnology Center, Nagoya University.

Mechanism regulating Ca2+-dependent mechanosensory behaviour in sea urchin spermatozoa. Cell Structure and Function , 36: 69-82.

Figure 1

Fig. 1. Swimming trajectories of sperm heads before and after mechanical stimulation

Figure 2

Fig. 2. Schematic diagram showing a model of the mechanism regulating the Ca2+ - dependent mechanosensory response in sea urchin sperm