The first mitosis of the mammalian embryo must partition the parental genomes contained in two pronuclei. In rodent zygotes, sperm centrosomes are degraded, and instead, acentriolar microtubule organizing centers and microtubule self-organization guide the assembly of two separate spindles around the genomes. In nonrodent mammals, including human or bovine, centrosomes are inherited from the sperm and have been widely assumed to be active. Whether nonrodent zygotes assemble a single centrosomal spindle around both genomes or follow the dual spindle self-assembly pathway is unclear. To address this, we investigated spindle assembly in bovine zygotes by systematic immunofluorescence and real-time light-sheet microscopy. We show that two independent spindles form despite the presence of centrosomes, which had little effect on spindle structure and were only loosely connected to the two spindles. We conclude that the dual spindle assembly pathway is conserved in nonrodent mammals. This could explain whole parental genome loss frequently observed in blastomeres of human IVF embryos.

中文翻译：

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尽管存在父本中心体，双纺锤体仍在牛受精卵中组装

哺乳动物胚胎的第一次有丝分裂必须将亲本基因组分成两个原核。在啮齿动物受精卵中，精子中心体被降解，取而代之的是，无心粒微管组织中心和微管自组织引导基因组周围两个独立纺锤体的组装。在非啮齿类哺乳动物中，包括人类或牛，中心体是从精子继承的，并且被广泛认为是活跃的。非啮齿动物受精卵是否在两个基因组周围组装单个中心体纺锤体或遵循双纺锤体自组装途径尚不清楚。为了解决这个问题，我们通过系统免疫荧光和实时光片显微镜研究了牛受精卵中的纺锤体组装。我们发现，尽管存在中心体，但仍形成两个独立的纺锤体，这对纺锤体结构影响很小，并且仅与两个纺锤体松散连接。我们得出的结论是，双纺锤体组装途径在非啮齿类哺乳动物中是保守的。这可以解释在人类体外受精胚胎卵裂球中经常观察到的整个亲本基因组丢失的现象。