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 non-rodent mammals, including human or bovine, centrosomes are inherited from the sperm and have been widely assumed to be active. Whether non-rodent 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 around the parental genomes 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 non-rodent mammals. This could explain whole parental genome loss frequently observed in blastomeres of human IVF embryos.

中文翻译：

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尽管有父本中心体，但非啮齿动物哺乳动物受精卵仍会组装双纺锤体

哺乳动物胚胎的第一个有丝分裂必须划分两个原核中包含的亲本基因组。在啮齿动物的受精卵中，精子中心体被降解，取而代之的是，小人孔微管组织中心和微管自组织指导了围绕基因组的两个独立纺锤体的组装。在包括人或牛在内的非啮齿类哺乳动物中，中心体是从精子遗传而来，并被广泛认为具有活性。尚不清楚非啮齿动物合子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。为了解决这个问题，我们通过系统的免疫荧光和实时光片显微镜研究了牛合子中的纺锤体组装。我们显示，尽管存在着中心体，但两个独立的纺锤体围绕父母基因组形成，对主轴的结构影响很小，只是松散地连接到两个主轴上。我们得出的结论是，在非啮齿动物中，双梭组装途径是保守的。这可以解释在人IVF胚胎的卵裂球中经常观察到的整个亲本基因组丢失。