Cleine J H, Dixon K E
J Embryol Exp Morphol. 1985 Dec;90:79-99.
Eggs of X. laevis were rotated (sperm entrance point downwards) either through 90 degrees (1 X 90 embryos) or 180 degrees in two 90 degrees steps (2 X 90 embryos) at approximately 25-30 min postfertilization after cooling to 13 degrees C. The embryos were kept in their off-axis orientation and cooled until the early gastrula stage. Rotation resulted in relocation of egg constituents with slight changes in the distribution of outer cortical and subcortical components and major changes in inner constituents where the heavy yolk and cytoplasm appeared to reorient as a single coherent unit to maintain their relative positions with respect to gravity. Development of rotated embryos was such that regions of the egg which normally give rise to posterior structures instead developed into anterior structures and vice versa. Germ plasm was displaced in the vegetal-dorsal-animal direction (the direction of rotation) and was segregated into dorsal micromeres and intermediate zone cells in 2 X 90 embryos and dorsal macromeres and intermediate zone cells in 1 X 90 embryos. In consequence, at the gastrula stage, cells containing germ plasm were situated closer to the dorsal lip of the blastopore after rotation--in 2 X 90 gastrulas around and generally above the dorsal lip. Hence, in rotated embryos, the cells containing germ plasm were invaginated earlier during gastrulation and therefore were carried further anteriorly in the endoderm to a mean position anterior to the midpoint of the endoderm. The number of cells containing germ plasm in rotated embryos was not significantly different from that in controls at all stages up to and including tail bud (stage 25). However at stages 46, 48 and 49 the number of primordial germ cells was reduced in 1 X 90 embryos in one experiment of three and in 2 X 90 embryos in all experiments. We tested the hypothesis that the decreased number of primordial germ cells in the genital ridges was due to the inability of cells to migrate to the genital ridges from their ectopic location in the endoderm. When anterior endoderm was grafted into posterior endodermal regions the number of primordial germ cells increased slightly or not at all suggesting that the anterior displacement of the cells containing germ plasm was not the only factor responsible for the decreased number of primordial germ cells in rotated embryos. Other possible explanations are discussed.
在受精后约25 - 30分钟，将非洲爪蟾的卵冷却至13摄氏度，然后将其旋转（精子进入点向下），要么旋转90度（1×90胚胎组），要么分两步每次旋转90度共旋转180度（2×90胚胎组）。胚胎保持其偏轴方向并继续冷却，直到早期原肠胚阶段。旋转导致卵成分重新定位，外层皮质和皮质下成分的分布略有变化，而内部成分发生重大变化，重质卵黄和细胞质似乎作为一个连贯的单元重新定向，以保持它们相对于重力的相对位置。旋转胚胎的发育情况是，卵中通常产生后部结构的区域反而发育成前部结构，反之亦然。生殖质沿植物 - 背 - 动物方向（旋转方向）移位，在2×90胚胎组中被分隔到背侧小卵裂球和中间带细胞中，在1×90胚胎组中被分隔到背侧大卵裂球和中间带细胞中。因此，在原肠胚阶段，旋转后含有生殖质的细胞位于更靠近胚孔背唇的位置——在2×90原肠胚中围绕并通常在背唇上方。因此，在旋转胚胎中，含有生殖质的细胞在原肠胚形成期间更早内陷，因此在中胚层中被进一步带到更靠前的位置，到达中胚层中点前方的平均位置。在包括尾芽（第25阶段）在内的所有阶段，旋转胚胎中含有生殖质的细胞数量与对照组相比无显著差异。然而，在第46、48和49阶段，在三项实验中的一项实验里，1×90胚胎组中原生殖细胞数量减少，在所有实验的2×90胚胎组中也减少。我们检验了这样一个假设，即生殖嵴中原生殖细胞数量减少是由于细胞无法从其在内胚层中的异位位置迁移到生殖嵴。当将前部内胚层移植到后部内胚层区域时，原生殖细胞数量略有增加或根本没有增加，这表明含有生殖质的细胞向前移位不是旋转胚胎中原生殖细胞数量减少的唯一原因。文中还讨论了其他可能的解释。
