Cline C A, Schatten H, Balczon R, Schatten G
Cell Motil. 1983;3(5-6):513-24. doi: 10.1002/cm.970030518.
The sea urchin egg at fertilization is an ideal model in which to study actin-mediated surface activity. Electron microscopy of unfertilized eggs demonstrates the presence of thousands of well-arrayed short microvilli, which appear supported by cytochalasin-sensitive actin oligomers as detected with rhodamine-labeled phalloidin staining of permeabilized eggs. At insemination, the previously short microvilli elongate and cluster around the successful sperm during incorporation. Phalloidin staining demonstrates a tremendous recruitement of polymerized actin into the site of sperm incorporation, resulting in the formation of the fertilization cone. Fertilization of cytochalasin-treated eggs results in the normal activation of the metabolic and bioelectric events, but sperm incorporation does not occur since the localized actin assembly required for fertilization cone formation is precluded. After sperm incorporation, the entire fertilized surface is restructured, as a result of a massive polymerization of actin to produce a burst in microvillar elongation. Addition of cytochalasin to eggs immediately following sperm incorporation demonstrates the recruitment of actin assembly for the proper progression through the first cell cycle. During normal cell division, the egg surface retains the long microvilli. The furrow which forms at cytokinesis does not appear as a unique new structure, but rather as a reorganization of the cortical microfilaments. Quantitative fluorescence microscopy argues against an increase in microfilaments during early cytokinesis. At the latest stages of cytokinesis, a thickening of the cortical actin is noted, which could possibly be interpreted as a contractile ring. A minor basal level of actin assembly with numerous nucleation sites in unfertilized eggs and a tremendous but localized assembly of microfilaments surrounding the sperm during incorporation, followed by a massive global microfilament assembly event to elongate the fertilized egg microvilli resulting later in the reorganization of these microfilaments to produce the forces necessary for cytokinesis, highlight the utility of the study of sea urchin eggs at fertilization for understanding actin-membrane interactions.
受精时的海胆卵是研究肌动蛋白介导的表面活性的理想模型。未受精卵的电子显微镜观察显示存在数千根排列整齐的短微绒毛，用罗丹明标记的鬼笔环肽对通透处理的卵进行染色检测发现，这些微绒毛似乎由细胞松弛素敏感的肌动蛋白寡聚体支撑。受精时，先前的短微绒毛会伸长并在精子成功进入时聚集在其周围。鬼笔环肽染色显示大量聚合的肌动蛋白被募集到精子进入的部位，从而形成受精锥。用细胞松弛素处理的卵受精后，代谢和生物电事件会正常激活，但由于受精锥形成所需的局部肌动蛋白组装被阻止，精子无法进入。精子进入后，整个受精表面会发生重组，这是由于肌动蛋白大量聚合导致微绒毛伸长激增的结果。精子进入后立即向卵中添加细胞松弛素表明，肌动蛋白组装的募集对于正常通过第一个细胞周期是必要的。在正常细胞分裂过程中，卵表面保留着长微绒毛。胞质分裂时形成的沟并不是一个独特的新结构，而是皮质微丝的重新组织。定量荧光显微镜观察结果表明，在早期胞质分裂过程中微丝数量没有增加。在胞质分裂的最后阶段，注意到皮质肌动蛋白增厚，这可能被解释为收缩环。未受精卵中存在少量具有众多成核位点的基础水平肌动蛋白组装，受精时精子周围会发生大量但局部的微丝组装，随后是大规模的整体微丝组装事件，导致受精卵微绒毛伸长，随后这些微丝重新组织以产生胞质分裂所需的力，这突出了研究受精时的海胆卵对于理解肌动蛋白与膜相互作用的实用性。
