不同发育时期哲罗鱼卵黄的超微结构

应用透射电镜观察了不同发育时期哲罗鱼(Hucho taimen)卵黄的超微结构.根据哲罗鱼卵黄物质在卵母细胞中的加工合成、积累以及卵母细胞中参与卵黄颗粒形成的细胞器的变化,可将该鱼卵黄发生分为4个特征时期,即卵黄发生前期、卵黄泡期、卵黄积累期和卵黄积累完成期.卵黄发生前期是指卵母细胞发育过程中的卵黄物质开始积累前的时期,此时期核仁不断分裂,出现线粒体云和早期的滤泡细胞层、基层和鞘细胞层；卵黄泡期特点主要是细胞器不断变化产生卵黄泡和皮层泡；卵黄积累期的滤泡膜由内向外依次为放射带、颗粒细胞层、基层和鞘细胞层,此时外源性卵黄前体物质不断经过血液汇集于鞘细胞层,后经微胞饮作用穿过胶原纤维组成的基层,经过多泡体作用转运至颗粒细胞内,在细胞内经过加工和修饰形成小的卵黄蛋白颗粒,卵黄蛋白颗粒经微胞饮穿过放射带进入卵母细胞边缘形成的空泡中,不断积累形成卵黄球；进入卵黄积累完成期,卵黄球体积变大,向细胞中心聚集,填满大部分卵母细胞,卵黄积累完毕.

The Ultrastructure of Vitellogenesis in Hucho taimen at Different Developmental Stages

The ultrastructure of vitellogenesis was observed by the transmission electron microscopy in Hucho taimen at different developmental stages. The results indicated that the yolk of H.taimen was concentrated mainly at primary oocyte phase. On the basis of the composition and accumulation of yolk and change of organelle participating in the formation of the vitellus granule in oocyte, the vitellogenesis was divided into four phases: Provitellogenic stage, vitelline vacuole stage, vitelline accumulation stage, vitelline accumulation completion stage. The provitellogenic stage refers to the period before the yolk material begins to accumulate in the process of oocyte development. During this period, the nucleolus disintegrated unceasingly and clusters of mitochondria appeared, meanwhile, three layers of functional membrane structure formed outside the oocyte. The organelle changed unceasingly, yolk vacuoles and cortical vesicles generated at the vitelline vacuole stage. At the vitelline accumulation stage, the membrane of follicle was made up of zona radiata, granular cells layer, basement layer and sheath cell layer in order while the exogenous yolk material accumulated in sheath cell layer through blood flow, then went through basement layer by micro-pinocytosis, and finally reached granulosa cells by multivesicular body action, where yolk protein particles formed by processing and modification of the protein. The yolk protein particles went through zona radiata by micropinocytosis and aggregated into the vacuoles that formed at the periphery of oocyte and accumulated to from yolk globules. At the vitelline accumulation completion stage, the volume of yolk globules that assembled to the center of cell was increased and a majority of the oocyte was full of yolk globules, and the yolk accumulation was accomplished.