Tilney L G, Kallenbach N
J Cell Biol. 1979 Jun;81(3):608-23. doi: 10.1083/jcb.81.3.608.
The polarity of the actin filaments which assemble from the nucleating body or actomere of Thyone and Pisaster sperm was determined using myosin subfragment 1 decoration. The polarity was found to be unidirectional with the arrowheads pointing towards the cell center. When polymerization is induced at low temperature with concentrations of actin near the critical concentration for polymerization, elongation of filaments occurs preferentially off the apical end. If the sperm are induced to undergo the acrosomal reaction with an ionophore, the polarity of the actin filaments attached to the actomere is the same as that already described, but the filaments which polymerize parallel to, but peripheral to, those extending from the actomere are randomly polarized. These randomly polarized filaments appear to result from spontaneous nucleation. When sperm are induced to undergo the acrosomal reaction with eggs, the polarity of the actin filaments is also unidirectional with the arrowheads pointing towards the cell center. From these results we conclude: (a) that the actomere, by nucleating the polymerization of actin filaments, controls the polarity of the actin filaments in the acrosomal process, (b) that the actomere recognizes a surface of the actin monomer that is different from that surface recognized by the dense material attached to membranes, and (c) that egg myosin could not act to pull the sperm into the egg. Included is a discussion of how the observation that monomers add largely to one end of a decorated filament in vitro relates to these in vivo observations.
利用肌球蛋白亚片段1标记法，确定了从海胆（Thyone）和海盘车（Pisaster）精子的成核体或肌动粒组装而成的肌动蛋白丝的极性。结果发现极性是单向的，箭头指向细胞中心。当在低温下用接近聚合临界浓度的肌动蛋白浓度诱导聚合时，丝的伸长优先发生在顶端之外。如果用离子载体诱导精子发生顶体反应，附着在肌动粒上的肌动蛋白丝的极性与上述相同，但与从肌动粒延伸出的丝平行但位于其外周聚合的丝是随机极化的。这些随机极化的丝似乎是由自发成核产生的。当用卵子诱导精子发生顶体反应时，肌动蛋白丝的极性也是单向的，箭头指向细胞中心。从这些结果我们得出结论：（a）肌动粒通过引发肌动蛋白丝的聚合，在顶体过程中控制肌动蛋白丝的极性；（b）肌动粒识别肌动蛋白单体的一个与附着在膜上的致密物质所识别的表面不同的表面；（c）卵子肌球蛋白不能起到将精子拉入卵子的作用。文中还讨论了在体外观察到单体主要添加到标记丝一端的现象与这些体内观察结果之间的关系。
