Detmers P A
Can J Biochem Cell Biol. 1985 Jun;63(6):599-607. doi: 10.1139/o85-078.
The acrosomal processes of Thyone and Limulus sperm and the fertilization tubule of mt+ gametes of Chlamydomonas are interesting models for actin-based motility. Each is a long thin process that elongates rapidly and contains a core of actin filaments having uniform polarity: arrowheads formed by myosin subfragments point toward the base of the processes. In Limulus, directed outgrowth of the acrosomal process is achieved by a rearrangement in the packing of superhelically coiled actin filaments that form during spermatogenesis. In contrast, outgrowth of the acrosomal process in Thyone and the fertilization tubule in Chlamydomonas is accompanied by actin polymerization. Both Thyone and Chlamydomonas possess structures, the actomere and the doublet zone, respectively, that serve as microfilament organizing centers, nucleating actin polymerization and defining the polarity of the growing filaments. Alkalinization of the cytoplasm may promote polymerization of actin in Thyone, whereas an apparent rise in the intracellular Ca2+ concentration is associated with the transmission of intracellular signals during mating in Chlamydomonas. Further examination of these three actin-based motile systems should provide new insights into the assembly of the actin cytoskeleton, a process critical for many forms of nonmuscle cellular motility.
海胆和鲎精子的顶体突起以及衣藻mt+配子的受精管是基于肌动蛋白运动的有趣模型。每一个都是细长的突起，能迅速伸长，并且包含具有统一极性的肌动蛋白丝核心：由肌球蛋白亚片段形成的箭头指向突起的基部。在鲎中，顶体突起的定向生长是通过精子发生过程中形成的超螺旋盘绕肌动蛋白丝堆积的重排实现的。相比之下，海胆的顶体突起和衣藻的受精管的生长伴随着肌动蛋白聚合。海胆和衣藻分别拥有作为微丝组织中心的结构，即动粒和双联体区，它们使肌动蛋白聚合并确定生长丝的极性。细胞质碱化可能会促进海胆中肌动蛋白的聚合，而衣藻交配过程中细胞内Ca2+浓度的明显升高与细胞内信号传递有关。对这三种基于肌动蛋白的运动系统的进一步研究应该能为肌动蛋白细胞骨架的组装提供新的见解，这一过程对许多形式的非肌肉细胞运动至关重要。
