Tilney L G, Clain J G, Tilney M S
J Cell Biol. 1979 Apr;81(1):229-53. doi: 10.1083/jcb.81.1.229.
The membranes of Limulus (horseshoe crab) sperm were examined before and during the acrosomal reaction by using the technique of freeze-fracturing and thin sectioning. We focused on three areas. First, we examined stages in the fusion of the acrosomal vacuole with the cell surface. Fusion takes place in a particle-free zone which is surrounded by a circlet of particles on the P face of the plasma membrane and an underlying circlet of particles on the P face of the acrosomal vauole membrane. These circlets of particles are present before induction. Up to nine focal points of fusion occur within the particle-free zone. Second, we describe a system of fine filaments, each 30 A in diameter, which lies between the acrosomal vacuole and the plasma membrane. These filaments change their orientation as the vacuole opens, a process that takes place in less than 50 ms. Membrane particles seen on the P face of the acrosomal vacuole membrane change their orientation at the same time and in the same way as do the filaments, thus indicating that the membrane particles and filaments are probably connected. Third, we examined the source and the point of fusion of new membrane needed to cover the acrosomal process. This new membrane is almost certainly derived from the outer nuclear envelope and appears to insert into the plasma membrane in a particle-free area adjacent to an area rich in particles. The latter is the region where the particles are probably connected to the cytoplasmic filaments. The relevance of these observations in relation to the process of fertilization of this fantastic sperm is discussed.
利用冷冻断裂和超薄切片技术，对鲎精子顶体反应前后的细胞膜进行了检查。我们重点关注了三个方面。首先，我们研究了顶体泡与细胞表面融合的各个阶段。融合发生在一个无颗粒区，该区域在质膜的P面上被一圈颗粒包围，在顶体泡膜的P面上有一圈位于其下方的颗粒。这些颗粒圈在诱导之前就已存在。在无颗粒区内最多可出现九个融合焦点。其次，我们描述了一个细丝系统，每根细丝直径为30埃，位于顶体泡和质膜之间。随着顶体泡打开，这些细丝会改变其方向，这一过程在不到50毫秒内发生。在顶体泡膜的P面上看到的膜颗粒与细丝同时以相同方式改变其方向，因此表明膜颗粒和细丝可能是相连的。第三，我们研究了覆盖顶体突起所需新膜的来源和融合点。这种新膜几乎肯定来自外核膜，并且似乎在富含颗粒区域相邻的无颗粒区域插入质膜。后者是颗粒可能与细胞质细丝相连的区域。讨论了这些观察结果与这种奇妙精子受精过程的相关性。
