Space asymmetry directs preferential sperm entry in the absence of polarity in the mouse oocyte
Space asymmetry directs preferential sperm entry in the absence of polarity in the mouse oocyte
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DOI：
10.1371/journal.pbio.0040135
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发表时间：
2006-05-01
期刊：
影响因子：
9.8
通讯作者：
Hiiragi, Takashi
中科院分区：
文献类型：
--
作者：
Motosugi, Nami;Dietrich, Jens-Erik;Hiiragi, Takashi
了解胚胎极性形成的机制是了解哺乳动物发育的基础。在重新解决几个有争议的说法，我们最近提出了一个模型，其中小鼠胚胎极性不指定，直到囊胚阶段。在受精之前，完全分化的卵母细胞被描述为“极化的”，我们确实观察到精子优先进入极体的一半。在这里，我们表明，精子优先进入是不是由于卵母细胞的内在极性，因为受精发生均匀时，透明膜被删除。我们认为，术语“不对称”表示形态差异，而“极性”，另外意味着发展的后果。因此，小鼠卵母细胞可以被认为是“不对称的”但“非极化的”。“穿透透明膜也是随机的，相当大比例的精子在远离透明膜穿透部位的一个点上结合到卵母细胞膜上。延时记录证实，精子在受精前围绕卵周空间游动。实验性扩大非极体一半的卵周间隙增加了受精的区域概率。基于这些实验，我们提出了一个模型，在该模型中，由第一极体和透明质酸施加的空间不对称性引导精子优先进入极体的一半，而不需要卵母细胞的极性。
Knowledge about the mechanism that establishes embryonic polarity is fundamental in understanding mammalian development. In re-addressing several controversial claims, we recently proposed a model in which mouse embryonic polarity is not specified until the blastocyst stage. Before fertilization, the fully differentiated oocyte has been characterized as "Polarized," and we indeed observed that the sperm preferentially enters the polar body half. Here we show that preferential sperm entry is not due to an intrinsic polarity of the oocyte, since fertilization takes place uniformly when the zona pellucida is removed. We suggest that the term "asymmetry" denotes morphological differences, whereas "polarity" in addition implies developmental consequences. Thus, the mouse oocyte can be considered "asymmetric" but "non-polarized." The penetration through the zona pellucida is also random, and a significant proportion of sperm binds to the oocyte membrane at a point distant from the zona penetration site. Time-lapse recordings confirmed that sperm swim around the perivitelline space before fertilization. Experimental enlargement of the perivitelline space in the non-polar body half increased the regional probability of fertilization. Based on these experiments, we propose a model in which the space asymmetry exerted by the first polar body and the zona pellucida directs sperm entry preferentially to the polar body half, with no need for oocyte polarity.