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Sperm-egg fusion in the sea urchin is blocked in Mg2+-free seawater

Published online by Cambridge University Press:  26 September 2008

Hideo Mohri*
Affiliation:
University of the Air, Tokyo Institute of Technology, Hokkaido University and Tokyo Women's Medical College, Japan.
Yukihisa Hamaguchi
Affiliation:
University of the Air, Tokyo Institute of Technology, Hokkaido University and Tokyo Women's Medical College, Japan.
Miyako S. Hamaguchi
Affiliation:
University of the Air, Tokyo Institute of Technology, Hokkaido University and Tokyo Women's Medical College, Japan.
Kiyoshi Sano
Affiliation:
University of the Air, Tokyo Institute of Technology, Hokkaido University and Tokyo Women's Medical College, Japan.
Hideki Shirakawa
Affiliation:
University of the Air, Tokyo Institute of Technology, Hokkaido University and Tokyo Women's Medical College, Japan.
Ken Nakada
Affiliation:
University of the Air, Tokyo Institute of Technology, Hokkaido University and Tokyo Women's Medical College, Japan.
Shunichi Miyazaki
Affiliation:
University of the Air, Tokyo Institute of Technology, Hokkaido University and Tokyo Women's Medical College, Japan.
*
Professor Hideo Mohri, University of the Air, Wakaba 2-11, Mihama-ku, Chiba 261, Japan. Tel: 043-276-5111. Fax: 043-275-9726.

Summary

Magnesium ions as well as calcium ions are required for successful fertilisation in sea urchins. In the absence of Mg2+ spermatozoa attached to the egg plasma membrane, their acrosomal processes passing through the vitelline envelope, but could not enter the egg cytoplasm (Sano et al, Dev. Growth Differ. 22, 531–41,1980). Such an individual spermatozoon was observed microscopically to resume entry into the egg immediately after the addition of a sufficient amount of Mg2+ to the surrounding medium. Neither any change in membrane potential nor an increase in intracellular Ca2+ concentration of the egg was observed after insemination in the absence of Mg2+, although both could be observed after the addition of Mg2+. The sperm heads did not show fluorescence when attached to the surface of an egg previously microinjected with mithramycin A in Mg-free seawater, indicating that there was no connection between the sperm and the egg. Therefore, occurrence of fertilisation potential must be a post-fusional event. These results suggest that Mg2+ are indispensable for fusion between the sperm acrosomal membrane and the egg plasma membrane.

Type
Article
Copyright
Copyright © Cambridge University Press 1994

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