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24 March 2017 Chemical and physical guidance of fish spermatozoa into the egg through the micropyle
Ryuzo Yanagimachi, Tatsuo Harumi, Hajime Matsubara, Wei Yan, Shuiqiao Yuan, Noritaka Hirohashi, Tomohiro Iida, Etsuro Yamaha, Katsutoshi Arai, Takahiro Matsubara, Tadashi Andoh, Carol Vines, Gary N. Cherr
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Abstract

Eggs of teleost fish, unlike those of many other animals, allow sperm entry only at a single site, a narrow canal in the egg's chorion called the micropyle. In some fish (e.g., flounder, herring, and Alaska pollock), the micropyle is a narrow channel in the chorion, with or without a shallow depression around the outer opening of micropyle. In some other fish (e.g., salmon, pufferfish, cod, and medaka), the micropyle is like a funnel with a conical opening. Eggs of all the above fish have a glycoprotein tightly bound to the chorion surface around the micropyle. This glycoprotein directs spermatozoa into the micropylar canal in a Ca2 -dependent manner. This substance, called the micropylar sperm attractant or MISA, increases fertilization efficiency and is essential in herring. In flounder, salmon, and perhaps medaka, fertilization is possible without MISA, but its absence makes fertilization inefficient because most spermatozoa swim over the micropyle without entering it. The mechanism underlying sperm-MISA interactions is yet to be determined, but at least in herring the involvement of Ca2 and K channel proteins, as well as CatSper and adenylyl cyclase, is very likely. In some other fish (e.g., zebrafish, loach, and goldfish), the chorion around the micropyle is deeply indented (e.g., zebrafish and loach) or it has radially or spirally arranged grooves around the outer opening of the micropyle (e.g., goldfish). MISA is absent from the eggs of these fish and sperm entry into micropylar canal seems to be purely physical.

Summary Sentence

In fish, sperm entry into the egg through the micropyle is guided either chemically or physically depending on the species

© The Authors 2017. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved. For permissions, please journals.permissions@oup.com
Ryuzo Yanagimachi, Tatsuo Harumi, Hajime Matsubara, Wei Yan, Shuiqiao Yuan, Noritaka Hirohashi, Tomohiro Iida, Etsuro Yamaha, Katsutoshi Arai, Takahiro Matsubara, Tadashi Andoh, Carol Vines, and Gary N. Cherr "Chemical and physical guidance of fish spermatozoa into the egg through the micropyle," Biology of Reproduction 96(4), 780-799, (24 March 2017). https://doi.org/10.1093/biolre/iox015
Received: 15 February 2017; Accepted: 21 March 2017; Published: 24 March 2017
JOURNAL ARTICLE
20 PAGES


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