The early blastocyst is bilaterally symmetrical and its axis of symmetry is aligned with the animal-vegetal axis of the zygote in the mouse.
The early blastocyst is bilaterally symmetrical and its axis of symmetry is aligned with the animal-vegetal axis of the zygote in the mouse.
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作者：
Richard L. Gardner
至少有一个极体，几乎总是第二个，持续完整的早期胚泡阶段，在近三分之二的小鼠概念的PO株。这些存活极体在早期囊胚中的分布是高度非随机的。大多数不仅位于胚胎-非胚轴的中间区域，而且发现早期囊胚是双侧的，而不是关于该轴径向对称的，发现与双侧轴对齐。细胞标记实验未能检测到极体相对于卵裂或囊胚形成过程中的孕体表面的运动。退化的极体和它们的碎片的分布与完整的相似，这也反对它们的运动性，因为在所有阶段，第二极体都是通过一条薄的、可伸展的、弱弹性的“系绳”附着在孕体上的。虽然它们之间的小荧光染料的转移很少观察到超过第二卵裂，第二极体和孕体可以保持耦合到囊胚阶段的离子。它的结论是，第二极体通常保持附着在孕体通过持久性的细胞间的桥梁，在其abstriction期间形成的，因此提供了一个持久的标记的动物极的受精卵。因此，根据极体的分布，早期囊胚的双侧对称轴通常与合子的动物-植物轴对齐，其胚胎-非胚轴与之正交。这种关系表明，至少在不受干扰的发育中，囊胚轴的规格取决于合子的空间模式。
At least one polar body, almost invariably the second, persists intact to the early blastocyst stage in nearly two-thirds of mouse conceptuses of the PO strain. The distribution in early blastocysts of these surviving polar bodies was highly non-random. Most not only lay in the mid-region of the embryonic-abembryonic axis but, on discovering that early blastocysts are bilaterally rather than radially symmetrical about this axis, were found to align with the bilateral axis. Cell marking experiments failed to detect movement of polar bodies relative to the surface of the conceptus during either cleavage or blastulation. That the distribution of degenerating polar bodies and their presumed debris was similar to intact ones also argued against their motility, as did the finding that at all stages second polar bodies were attached to conceptuses by a thin, extensible, weakly elastic 'tether'. Although the transfer of small fluorochromes between them was rarely observed beyond second cleavage, the second polar body and conceptus could remain coupled ionically up to the blastocyst stage. It is concluded that the second polar body normally remains attached to the conceptus through persistence of the intercellular bridge formed during its abstriction, and therefore provides an enduring marker of the animal pole of the zygote. Hence, according to the distribution of polar bodies, the axis of bilateral symmetry of the early blastocysts is normally aligned with the animal-vegetal axis of the zygote and its embryonic-abembryonic axis is orthogonal to it. Such relationships suggest that, at least in undisturbed development, specification of the axes of the blastocyst depends on spatial patterning of the zygote.