title: Chemical and physical guidance of fish spermatozoa into the egg through the micropyle†,‡.
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.
authors.affiliation: Department of Anatomy, Biochemistry and Physiology, Institute for Biogenesis Research, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA.
authors.forename: Ryuzo
authors.initials: R
authors.lastname: Yanagimachi
authors.affiliation: Department of Anatomy, Asahikawa Medical University, Asahikawa, Hokkaido, Japan.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Harumi
authors.affiliation: Department of Aquatic Biology, Tokyo University of Agriculture, Abashiri, Hokkaido, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Matsubara
authors.affiliation: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Yan
authors.affiliation: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada, USA.
authors.forename: Shuiqiao
authors.initials: S
authors.lastname: Yuan
authors.affiliation: Oki Marine Biological Station, Shimane University, Okino-shima, Shimane, Japan.
authors.forename: Noritaka
authors.initials: N
authors.lastname: Hirohashi
authors.affiliation: Oki Marine Biological Station, Shimane University, Okino-shima, Shimane, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Iida
authors.affiliation: Nanae Fresh-water Laboratory, Field Science Center for Northern Biosphere, Hokkaido University, Nanae, Hokkaido, Japan.
authors.forename: Etsuro
authors.initials: E
authors.lastname: Yamaha
authors.affiliation: Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan.
authors.forename: Katsutoshi
authors.initials: K
authors.lastname: Arai
authors.affiliation: South Ehime Fishery Research Center, Ehime University, Ainan, Ehime, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Matsubara
authors.affiliation: Seikai National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Taira-machi, Nagasaki, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Andoh
authors.affiliation: Bodega Marine Laboratory, University of California Davis, Bodega Bay, California, USA.
authors.forename: Carol
authors.initials: C
authors.lastname: Vines
authors.affiliation: Bodega Marine Laboratory, University of California Davis, Bodega Bay, California, USA.
authors.forename: Gary N
authors.initials: GN
authors.lastname: Cherr
mesh_terms: D000818:Animals; D005306:Fertilization / Q000502:physiology; D005399:Fishes / Q000502:physiology*; D008297:Male; D010063:Ovum / Q000502:physiology*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013045:Species Specificity; D013075:Sperm Capacitation / Q000187:drug effects; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000502:physiology*
chemical_list: D015842:Serine Proteinase Inhibitors
keywords: chemotaxis; egg; fertilization; fish; micropyle; spermatozoa