Hamaguchi Yukihisa, Numata Taketoshi, K Satoh Setsuko
Department of Bioengineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, Japan.
Cell Struct Funct. 2007;32(1):29-40. doi: 10.1247/csf.06034. Epub 2007 Jun 18.
Polar body formation is an extremely unequal cell division. In order to understand the mechanism of polar body formation, morphological changes at the animal pole were investigated in living oocytes of the starfish, Asterina pectinifera, and the amounts of cortical actin filaments were quantitatively estimated after staining the maturing oocytes with fluorescently-labeled phallotoxins using a computer and image-processing software. Formation of a bulge, which is presumed to become a polar body, and the anaphase separation of chromosomes occurred simultaneously. When the bulge became large, one group of chromatids moved into the bulge. The dividing furrow then formed and finally a polar body formed. Just at the time of bulge formation, the intensity of the fluorescence produced by the actin filaments at the top of the animal pole began to decrease, and subsequently the intensity at the top fell to half of the original value. On the other hand, the fluorescence intensity at the base of the bulge increased gradually. This actin accumulation at the base created a dividing furrow around the top of the animal pole as the bulge grew. Even when the polar body formation was inhibited mechanically, a similar pattern of actin deficiency and accumulation in the cortex near the animal pole was observed. This indicates that such regulation of filamentous actin can take place without bulging. Therefore, polar body formation is initiated by the bulging of the cortex weakened by actin deficiency and followed by contraction of the base of the bulge reinforced by actin accumulation.
极体形成是一种极其不均等的细胞分裂。为了理解极体形成的机制，研究了海星（Asterina pectinifera）活卵母细胞动物极处的形态变化，并使用计算机和图像处理软件，在用荧光标记的鬼笔环肽对成熟卵母细胞染色后，定量估计皮质肌动蛋白丝的数量。一个被认为会变成极体的凸起的形成与染色体后期分离同时发生。当凸起变大时，一组染色单体移入凸起。然后形成分裂沟，最终形成一个极体。就在凸起形成时，动物极顶部肌动蛋白丝产生的荧光强度开始下降，随后顶部的强度降至原始值的一半。另一方面，凸起底部的荧光强度逐渐增加。随着凸起的生长，这种在底部的肌动蛋白积累在动物极顶部周围形成了一个分裂沟。即使机械抑制极体形成，在动物极附近的皮质中也观察到了类似的肌动蛋白缺乏和积累模式。这表明这种丝状肌动蛋白的调节可以在没有凸起的情况下发生。因此，极体形成是由因肌动蛋白缺乏而减弱的皮质凸起引发的，随后是因肌动蛋白积累而增强的凸起底部收缩。
