Tilney L G, Inoué S
J Cell Biol. 1982 Jun;93(3):820-7. doi: 10.1083/jcb.93.3.820.
Thyone sperm were induced to undergo the acrosomal reaction with a calcium ionophore A23187 in sea water containing 50 mM excess CaCl2, and the extension of the acrosomal process was recorded with high-resolution, differential interference contrast video microscopy at 60 fields/sec. The length of the acrosomal process was measured at 0.25-s intervals on nine sperm. When the data were plotted as (length)2 vs. time, the points fell exactly on a straight line except for the initial and very final stages of elongation. Cytochalasin B alters the rate of elongation of the acrosomal process in a dose-dependent way, inhibiting the elongation completely at high concentrations (20 micrograms/ml). However, no inhibition was observed unless excess Ca++ was added to sea water. The concentration of actin in the periacrosomal cup of the unreacted sperm is as high as 160 mg/ml; we calculate this concentration from the number and lengths of the actin filaments in a fully reacted sperm, and the volume of the periacrosomal cup in the unreacted sperm. These results are consistent with the hypothesis proposed earlier that monomers add to the ends of the actin filaments situated at the tip of the growing acrosomal process (the preferred end for monomer addition), and that the rate of elongation of the process is limited by diffusion of monomers from the sperm head (periacrosomal cup) to the tip of the elongating process. During the extension of the acrosomal process, a few blebs distributed along its lengths move out with the process. These blebs maintain a constant distance from the tip of the growing process. At maximum length, the straight acrosomal process slackens into a bow, and numerous new blebs appear. A few seconds later, the process suddenly straightens out again and sometimes actually contracts. The behavior of the blebs indicates that membrane is inserted at the base of the growing acrosomal process, and that membrane assembly and water uptake must be coupled to actin assembly during elongation. We discuss how the dynamic balance of forces seems to determine the shape of the growing acrosomal process, and how actin assembly may be controlled during the acrosomal reaction.
在含有50 mM过量氯化钙的海水中，用钙离子载体A23187诱导海胆精子发生顶体反应，并以60帧/秒的高分辨率微分干涉对比视频显微镜记录顶体突起的延伸情况。在九个精子上每隔0.25秒测量一次顶体突起的长度。当将数据绘制成（长度）²对时间的曲线时，除了伸长的初始和最终阶段外，各点恰好落在一条直线上。细胞松弛素B以剂量依赖的方式改变顶体突起的伸长速率，在高浓度（20微克/毫升）时完全抑制伸长。然而，除非向海水中添加过量的钙离子，否则未观察到抑制作用。未反应精子顶体杯周围肌动蛋白的浓度高达160毫克/毫升；我们根据完全反应精子中肌动蛋白丝的数量和长度以及未反应精子顶体杯的体积来计算该浓度。这些结果与早期提出的假设一致，即单体添加到位于生长中的顶体突起顶端的肌动蛋白丝的末端（单体添加的优先末端），并且突起的伸长速率受单体从精子头部（顶体杯）扩散到伸长突起顶端的限制。在顶体突起延伸过程中，沿其长度分布的一些小泡随着突起一起向外移动。这些小泡与生长突起的顶端保持恒定距离。在最大长度时，笔直的顶体突起松弛成弓形，并且出现许多新的小泡。几秒钟后，突起突然再次伸直，有时实际上会收缩。小泡的行为表明膜插入到生长中的顶体突起的基部，并且在伸长过程中膜组装和水分吸收必须与肌动蛋白组装相耦合。我们讨论了力的动态平衡似乎如何决定生长中的顶体突起的形状，以及在顶体反应过程中肌动蛋白组装可能如何受到控制。
