Friend D S
Soc Gen Physiol Ser. 1980;34:153-65.
Normal fertilization in mammals depends on several events involving membrane fusion. One, a secretory phenomenon, is the fusion of the spermatozoan acrosomal granule membrane with the plasmalemma, and another concerns the union of this nascent hybrid membrane with that of the egg. Using freeze-fracture and ancillary cytochemical procedures, we can identify three general membrane constituents: proteins, apparent as intramembranous particles; phospholipids, visible as smooth, particle-free areas; and sterols, observed as 25-nm ellipsoid protuberances when complexed in situ with the polyene antibiotic filipin. Freshly removed from the epididymis, guinea pig sperm displays distinctive patterns of intramembranous particles and a nonhomogeneous distribution of sterols. When incubated in a Ca2+-free medium that permits processing spermatozoan membranes for fusion, these membrane components become altered. In the circular foci where union occurs, the particle pattern is modified from an orderly, geometric quilted design to a random distribution; filipin-reactive sterols are deleted, followed by the loss of particles from the nonesterified sterol-deficient patches. With the addition of Ca2+, the residual smooth areas meld as the number of particles equilibrates in the plane of the hybrid acrosomal-plasma membrane. Sterols appearing in the postacrosomal segment remain reduced in quantity. After acrosomal-plasma-membrane fusion, a second line of particle-cleared circles emerges behind the margin of the new membrane suture. These clearings appear to be identical to the circles observed in the acrosomal and plasma membranes preceding the acrosome reaction. We interpret this second series of clearings as the preparation of the spermatozoan membrane for fusion with the egg. In sperm, the focal alterations antecedent to organelle (acrosome) plasma membrane union are evidently comparable to those preceding plasma membrane (sperm) plasma membrane (egg) fusion. It will be of great interest to us to discover whether this type of protein and sterol/phospholipid juncture proves to be a unifying feature of fusions in all the various biological systems discussed in this volume.
哺乳动物的正常受精依赖于几个涉及膜融合的事件。其一，作为一种分泌现象，是精子顶体颗粒膜与质膜的融合，另一个则涉及这种新生杂种膜与卵膜的结合。运用冷冻断裂及辅助细胞化学方法，我们能够识别出三种一般的膜成分：蛋白质，表现为膜内颗粒；磷脂，呈现为光滑、无颗粒的区域；以及固醇，当与多烯抗生素制霉菌素在原位复合时，可观察为25纳米的椭圆形突起。刚从附睾取出的豚鼠精子呈现出独特的膜内颗粒模式以及固醇的非均匀分布。当在无钙培养基中孵育，该培养基允许处理精子膜以进行融合时，这些膜成分会发生改变。在发生结合的圆形区域，颗粒模式从有序的几何拼花图案转变为随机分布；制霉菌素反应性固醇消失，随后非酯化固醇缺乏区域的颗粒也丢失。随着钙离子的添加，残留的光滑区域融合，同时颗粒数量在顶体 - 质膜杂种平面达到平衡。顶体后段出现的固醇数量仍然减少。在顶体 - 质膜融合后，在新膜缝合边缘后方出现第二排颗粒清除的圆圈。这些清除区域似乎与顶体反应前在顶体膜和质膜中观察到的圆圈相同。我们将这第二系列的清除区域解释为精子膜为与卵融合所做的准备。在精子中，细胞器（顶体）质膜结合之前的局部改变显然与质膜（精子） - 质膜（卵）融合之前的改变相当。我们非常感兴趣去探究这种蛋白质与固醇/磷脂结合的类型是否被证明是本卷所讨论的所有各种生物系统中融合的一个统一特征。
