三疣梭子蟹精子顶体反应过程中的形态和结构变化

Morphological and structural changes of sperm during the acrosome reaction in the swimming crab Portunus trituberculatus

用离子载体A2 3187和卵水人工诱导三疣梭子蟹精子的顶体反应 ,分别获得 75 33%和 84 83%的顶体反应率。应用光镜和电镜技术观察了顶体反应前后精子形态和结构的变化。未处理精子呈陀螺形 ,由顶体、核杯和 5 - 10条核辐射臂组成。顶体包括顶体囊和顶体管。顶体囊的伞形头帽拥有约 70条辐射肋。连续发生的精子顶体反应过程被人为地分为四个阶段 :(1)头帽鼓起 ;(2 )顶体囊外翻 ;(3)穿孔器前伸 ,顶体囊膜翻转 ;(4 )顶体囊膜脱落 ,顶体丝形成。直到第四阶段才观察到钉状精子的辐射臂开始收缩。

The acrosome reaction (AR) of sperm from the swimming crab Portunus trituberculatus was induced artificially by treatment with ionophore A23187 (40 μg/ml) or egg-water. Female swimming crabs were collected from Shipu Port (Xiangshan, Zhejiang). The crabs were raised in a pond with aerated fresh sea water and fed with shellfish in March-April 2003. Sperm suspensions were prepared by squeezing and agitating the sperm pellets removed from the seminal receptacles. The sperm suspensions were used for artificial induction of the acrosome reaction. For collecting the egg-water, the ripe ovaries of the female crab which initiate to ovulate were teased into several fragments and soaked in 200 ml of filtered seawater at 4℃ for 24 h. 75.33% and 84.83% of acrosome reaction rate were achieved by treating the sperm with ionophore A23187 and egg-water respectively, and provided a sufficient number of reacted sperm to examine. Egg-water is a more effective and cheaper inducer of the acrosome reaction as compared with ionophore A23187. The morphological and structural changes of sperm during the acrosome reaction in P.trituberculatus were studied in detail with light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope(TEM). The mature sperm in the seminal receptacle has a top-like shape, and consists of an acrosome (A), nuclear cup (N) and (5-10) radial arms (RA) which extend from the nucleus. The spherial acrosome is comprised of acrosomal vesicle (AV) and acrosomal tubule (AT). The acrosomal vesicle surrouding the perforatorium (P) contains inner acrosomal material (IM), outer acrosomal material (OM), apical cap (AC) and subcap zone (SZ), and is limited by acrosomal vesicle membrane (AVM). The umbrella-like apical cap has approximately 70 rays radiating out of the acrosome vesicle membrane. So the apical cap is the only site liable to rupture to form an aperture. The process of acrosome reaction consists of four consecutive stages: (1) swelling of the apical cap and rupturing to form an aperture due to hydration; (2) initial release of the acrosomal material through the aperture and eversion of the acrosomal vesicle; (3) elongation of the perforatorium and subsequent reversal of the acrosomal vesicle membrane; and (4) separation of the acrosomal material, shedding of the acrosomal vesicle membrane at the thinkened ring (TR) and formation of the acrosomal filament (AF). The acrosomal filament consists of the perforatorium being the leading edge of the nail-like reacted sperm and the proximal piece (PP) deriving from the cytoplasmic lamellar complex (LC) of the unreacted sperm. During the acrosome reaction, the most noteworthy difference between the sperm of P.trituberculatus and that of Eriocheir sinensis or Scylla serrata is the behavior of the radial arms. In P.trituberculatus, the contraction of the radial arms can’t be observed until the 4th stage of the acrosome reaction. But in E.sinensis and S.serrata, the acrosome reaction starts with the contraction of the radial arms. Taking the nucleus as the datum line, the net forward movement of the perforatorium is about 2.5 μm during the acrosome reaction. The functions of the radial arm and the forward movement of the perforatorium in the penetration of sperm through the chorion are discussed .