Stewart-Savage J, Grey R D, Elinson R P
Department of Biological Science, University of New Orleans, Louisiana 70148.
J Electron Microsc Tech. 1991 Apr;17(4):369-83. doi: 10.1002/jemt.1060170402.
The anuran egg is polarized along its animal-vegetal axis and becomes bilaterally symmetrical before first cleavage. Functional sperm entry is regionally restricted to the animal hemisphere of the egg, and functional sperm entry does not occur after egg activation. This regional and functional restriction in sperm entry correlates with the presence of long, slender microvilli and with the presence of the filamentous component of the glycocalyx. After sperm fusion, the egg undergoes activation, including a depolarization of the membrane potential and exocytosis of granules in the cortex. Both of these activation responses are the result of a propagated increase in intracellular calcium. The egg's ability to undergo a propagated activation response develops after germinal vesicle breakdown and depends on the development of the cortical endoplasmic reticulum. Once activated, the radial symmetric egg acquires bilateral symmetry due to a rotation of the egg cortex relative to the inner cytoplasm. A transient array of parallel microtubules forms near the vegetal cortex and may be part of the motor driving the cortical rotation.
无尾两栖类卵沿动物-植物轴呈极性分布，在第一次卵裂前变为两侧对称。功能性精子进入在区域上局限于卵的动物半球，并且在卵激活后不会发生功能性精子进入。精子进入的这种区域和功能限制与长而细的微绒毛的存在以及糖萼丝状成分的存在相关。精子融合后，卵发生激活，包括膜电位去极化和皮质颗粒的胞吐作用。这两种激活反应都是细胞内钙传播性增加的结果。卵进行传播性激活反应的能力在生发泡破裂后发展，并取决于皮质内质网的发育。一旦被激活，由于卵皮质相对于内部细胞质的旋转，呈辐射对称的卵获得两侧对称。在植物皮质附近形成了一组短暂的平行微管阵列，可能是驱动皮质旋转的运动的一部分。
