日時： ２０１０年９月８日（水） １７：００〜１８：００
演題： Fertilization in sturgeon and function of its acrosome.
演者： Martin Psenicka （マルチン・ピシェニチカ）
北海道大学 大学院水産科学研究院 育種生物学分野
Sturgeon egg envelope consists of three principal layers, an outermost jelly coat, and a layer of cortical granules. The head of sturgeon spermatozoa is composed of a nucleus, a subacrosome and its acrosome with fingers-like posterolateral projections (PPs) and three intertwining endonuclear canals bounded by membranes traversed the nucleus in its whole length from the acrosome to the implantation fossa. The midpiece is equipped with a proximal and a distal centriole and from three to ten mitochondria. The flagellum contains an axoneme with “9+2” structure of microtubules. The sturgeon gametes differ from those of most fish in that their spermatozoa possess acrosome with PP, which number is species specific, whereas their eggs possess numerous micropyles.
The acrosome reaction includes formation of a long spear-like fertilization filament coming from 3 endonuclear canals and implantation fossa through the acrosome. It can accelerate the process of polyspermy prevention. Another unique feature of the acrosome is an anchor-like opening of PPs serving against release from the micropyle.
A generation of increasing perivitelline space by dissolution of the cortical granules is observed after contact of the fertilization filament with the cytoplasm of egg. A fertilization cone created from the egg cytoplasm blocked a fusion of other spermatozoa with cytoplasmic projection only in the fertilized micropyle.
The acrosomal reaction can be induced by solution containing Ca2+ in higher pH and screened using Soybean Trypsin Inhibitor-Alexa conjugate fluorescent staining. Hatching test using sperm with artificially disrupted acrosome proofed necessity of acrosomal integrity for fertilization. Increasing percentage of spermatozoa with disrupted acrosome highly decreased percentage of hatching, despite the treated spermatozoa were motile and electron microscopy verified that the spermatozoa with disrupted acrosomes reached the micropyle. This is supported with our other studies on comparison of sturgeon sperm cryopreservation with different extenders, whereas DMSO caused highest acrosome damages followed by lower hatching, despite the groups of sperm had similar motility parameters.