Black S D, Gerhart J C
Dev Biol. 1985 Apr;108(2):310-24. doi: 10.1016/0012-1606(85)90035-1.
In Xenopus laevis, the dorsal structures normally develop from regions of the egg opposite the side of sperm entry. Gravity is known to affect this topographic relationship in eggs inclined obliquely from their normal vertical orientation in the period before first cleavage. This effect has been explored in detail, making use of low-speed centrifugation (10-50 g) for short durations (4 min). Eggs were immobilized in gelatin and oriented with their animal-vegetal axes 90 degrees to the force vector, with the sperm entry point (SEP) side of the egg either toward or away from the center of the rotor. It has been found that the egg shows three distinct periods of response to centrifugal force in the interval from fertilization to first cleavage: Prior to 0.4 (40% of the first cleavage interval), the egg is very sensitive to centrifugal force and develops dorsal structures from its centrifugal side, regardless of the position of the SEP in the centrifugal field. Thus, the dorsal structures of the embryo are reversed from normal in eggs centrifuged with the SEP away from the center of the rotor. In the period 0.4 to 0.7, the egg is still very sensitive to centrifugal force and develops dorsal structures from its centripetal side, regardless of the position of the SEP in the centrifugal field. Thus, the dorsal structures of the embryo are reversed from normal in eggs centrifuged with the SEP toward the center of the rotor. In the period 0.7-1.0, the egg becomes increasingly resistant to centrifugal force and forms dorsal structures at the normal position opposite the SEP side. This resistance can be overcome in some egg clutches by 50 g centrifugation followed by prolonged 90 degrees off-axis inclination at 1g. Midway in the second cell cycle, there is a brief period of sensitivity to centrifugal force. These These results are discussed in terms of the types of cytoplasmic rearrangements occurring in the egg at different times of the cell cycle, and in terms of the process of cytoplasmic localization of determinants of dorsal axial development.
在非洲爪蟾中，背部结构通常从卵子中与精子进入一侧相对的区域发育而来。已知在第一次卵裂前的时期，重力会影响卵子从其正常垂直方向倾斜时的这种地形关系。利用低速离心（10 - 50克）短时间（4分钟）对这种效应进行了详细研究。卵子被固定在明胶中，其动物 - 植物轴与力向量成90度角定向，卵子的精子进入点（SEP）一侧朝向或远离转子中心。已发现卵子在受精到第一次卵裂的间隔期间对离心力表现出三个不同的反应阶段：在0.4（第一次卵裂间隔的40%）之前，卵子对离心力非常敏感，无论SEP在离心场中的位置如何，都会从其离心侧发育出背部结构。因此，在SEP远离转子中心进行离心的卵子中，胚胎的背部结构与正常情况相反。在0.4至0.7阶段，卵子对离心力仍然非常敏感，无论SEP在离心场中的位置如何，都会从其向心侧发育出背部结构。因此，在SEP朝向转子中心进行离心的卵子中，胚胎的背部结构与正常情况相反。在0.7 - 1.0阶段，卵子对离心力的抵抗力越来越强，并在与SEP侧相对的正常位置形成背部结构。在某些卵块中，可以通过50克离心，然后在1克下长时间偏离轴90度倾斜来克服这种抵抗力。在第二个细胞周期的中期，有一个对离心力敏感的短暂时期。这些结果根据细胞周期不同时间卵子中发生的细胞质重排类型以及背部轴向发育决定因素的细胞质定位过程进行了讨论。
