Yanagimachi Ryuzo, Harumi Tatsuo, Matsubara Hajime, Yan Wei, Yuan Shuiqiao, Hirohashi Noritaka, Iida Tomohiro, Yamaha Etsuro, Arai Katsutoshi, Matsubara Takahiro, Andoh Tadashi, Vines Carol, Cherr Gary N
Department of Anatomy, Biochemistry and Physiology, Institute for Biogenesis Research, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, USA.
Department of Anatomy, Asahikawa Medical University, Asahikawa, Hokkaido, Japan.
Biol Reprod. 2017 Apr 1;96(4):780-799. doi: 10.1093/biolre/iox015.
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.
硬骨鱼的卵与许多其他动物的卵不同，其精子只能从单个位点进入，即卵绒毛膜上一条狭窄的管道，称为卵孔。在一些鱼类（如比目鱼、鲱鱼和阿拉斯加狭鳕鱼）中，卵孔是绒毛膜中的一条狭窄通道，卵孔外开口周围有或没有浅凹陷。在其他一些鱼类（如鲑鱼、河豚、鳕鱼和青鳉）中，卵孔像一个有锥形开口的漏斗。上述所有鱼类的卵在卵孔周围的绒毛膜表面都紧密结合有糖蛋白。这种糖蛋白以钙离子依赖的方式引导精子进入卵孔管道。这种物质，称为卵孔精子吸引剂或MISA，可提高受精效率，对鲱鱼来说至关重要。在比目鱼、鲑鱼以及可能的青鳉中，没有MISA也可能受精，但缺少它会使受精效率低下，因为大多数精子会从卵孔上方游过而不进入。精子与MISA相互作用的潜在机制尚待确定，但至少在鲱鱼中，钙离子和钾离子通道蛋白以及CatSper和腺苷酸环化酶很可能参与其中。在其他一些鱼类（如斑马鱼、泥鳅和金鱼）中，卵孔周围的绒毛膜有深深的凹陷（如斑马鱼和泥鳅），或者在卵孔外开口周围有径向或螺旋状排列的凹槽（如金鱼）。这些鱼类的卵中不存在MISA，精子进入卵孔管道似乎完全是物理过程。
