Sperm attractant in the micropyle region of fish and insect eggs.

Ryuzo Yanagimachi, Gary Cherr, Takahiro Matsubara, Tadashi Andoh, Tatsuo Harumi, Carol Vines, Murali Pillai, Frederick Griffin, Hajime Matsubara, Tina Weatherby, Kenneth Kaneshiro

Institute for Biogenesis Research, Department of Anatomy, Physiology and Biochemistry, University of Hawaii Medical School, Honolulu, HI, USA. yana@hawaii.edu

Biology of reproduction 2013 Feb

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In some animals, such as fish, insects, and cephalopods, the thick egg coat has a narrow canal-a micropyle-through which spermatozoa enter the eggs. In fish, there is no indication that spermatozoa are attracted by eggs from a distance, but once spermatozoa come near the outer opening of the micropyle, they exhibit directed movement toward it, suggesting that a substance exists in this defined region to attract spermatozoa. Since Coomassie Blue (CB) binds preferentially to the micropyle region in flounder, herring, steelhead, and other fish, it probably stains this sperm guidance substance. This substance-a glycoprotein based on lectin staining-is bound tightly to the surface of the chorion, but can be removed readily by protease treatment. Although fertilization in fish (flounder) is possible after removal of this substance, its absence makes fertilization inefficient, as reflected by a drastic reduction in fertilization rate. The sperm "attraction" to the micropyle opening is species specific and is dependent on extracellular Ca(2+). Eggs of some insects, including Drosophila, have distinct micropyle caps with CB affinity, which also may prove to assist sperm entry. Our attempts to fertilize fly eggs in vitro were not successful.

Citation

Ryuzo Yanagimachi, Gary Cherr, Takahiro Matsubara, Tadashi Andoh, Tatsuo Harumi, Carol Vines, Murali Pillai, Frederick Griffin, Hajime Matsubara, Tina Weatherby, Kenneth Kaneshiro. Sperm attractant in the micropyle region of fish and insect eggs. Biology of reproduction. 2013 Feb;88(2):47