诱导栉孔扇贝雌核发育时精子入卵的扫描电镜观察

Scanning electron microscopic observation on sperm penetrating into eggs during artificial induction of gynogenetic Chlamys farreri

取栉孔扇贝 (Chlamysfarreri)精子在 80 0 μW/(cm2 ·s)的紫外线下辐射 ,然后与正常卵子受精 ,每隔 0 .5min取“受精卵”固定。在扫描电镜下连续观察精子的入卵过程 ,然后与正常精子的入卵过程进行比较。结果表明 ,紫外辐射后的精子可以划分为 3种类型 :I类精子 ,基本无明显变化 ,可以激发卵黄膜举起形成受精膜 ,同时诱发卵子发生皮层反应 ,在受精锥的作用下正常入卵 ,但入卵的时间较正常精子晚 ;II类精子 ,顶体膜破裂 ,顶体丝伸出 ;III类精子 ,顶体丝伸出 ,鞭毛脱落。由于II、III类精子在紫外辐射条件下诱发了顶体反应 ,融解卵膜的酶提前释放 ,因而不能入卵。精子鞭毛的脱落 ,使精子丧失了运动能力 ,是导致卵表面附着的精子数量较少的原因之一。无论是正常精子还是辐射后的精子 ,入卵后在卵表面都留下一个类似受精孔的通道。

Normal eggs ferterlized with sperms were irradiated by UV at the intensity of 800 μW/(cm^2·s). Then, some of the fertilized eggs were fixed into 4% formaldehyde and 1% glutaraldehyde in 0.5 min. The progress of sperm penetrating into eggs were observed under scanning electron microscope (SEM), and compared with that of normal ones. The results show that after irradiated, the sperms were divided into three types. Type I sperm, no apparent changes, could still induce the cortical reaction of the eggs. The vitelline membrane of eggs was elevated to form jelly membrane. And the sperms penetrated into the eggs with the help of fertilization cone like normal ones. But they need more time than normal sperms to enter into the eggs. Type II sperm underwent acrosomal reaction. Its acrosomal membrane cracked and its acrosomal processes extended. Type III sperm not only extended its acrosomal process, but also lost its flagellum. Both type II and type III could not penetrate into the eggs because they had undergone acrosomal reaction, having released the enzyme which would melt away the egg vitelline coats in advance. The lost of sperm flagellum, which is the main reason why there are rare sperms on the egg surface, makes the sperm lose moving ability. After the sperms penetrating into the eggs, a micropyle-like channel was left on the surface of the eggs in both experimental and control groups. There was no polyspermy in experimental group.