School of Biomedical Sciences, University of Newcastle, Callaghan, NSW 2308, Australia.
J Cell Sci. 2012 Dec 15;125(Pt 24):6030-7. doi: 10.1242/jcs.110155. Epub 2012 Oct 24.
In early embryos of a number of species the anaphase-promoting complex (APC), an important cell cycle regulator, requires only CDC20 for cell division. In contrast, fizzy-related-1 (FZR1), a non-essential protein in many cell types, is thought to play a role in APC activation at later cell cycles, and especially in endoreduplication. In keeping with this, Fzr1 knockout mouse embryos show normal preimplantation development but die due to a lack of endoreduplication needed for placentation. However, interpretation of the role of FZR1 during this period is hindered by the presence of maternal stores. In this study, therefore, we used an oocyte-specific knockout to examine FZR1 function in early mouse embryo development. Maternal FZR1 was not crucial for completion of meiosis, and furthermore viable pups were born to Fzr1 knockout females mated with normal males. However, in early embryos the absence of both maternal and paternal FZR1 led to a dramatic loss in genome integrity, such that the majority of embryos arrested having undergone only a single mitotic division and contained many γ-H2AX foci, consistent with fragmented DNA. A prominent feature of such embryos was the establishment of two independent spindles following pronuclear fusion and thus a failure of the chromosomes to mix (syngamy). These generated binucleate 2-cell embryos. In the 10% of embryos that progressed to the 4-cell stage, division was so slow that compaction occurred prematurely. No embryo development to the blastocyst stage was ever observed. We conclude that Fzr1 is a surprisingly essential gene involved in the establishment of a single spindle from the two pronuclei in 1-cell embryos as well as being involved in the maintenance of genomic integrity during the mitotic divisions of early mammalian embryos.
在许多物种的早期胚胎中，细胞周期调控因子后期促进复合物（APC）仅需要 CDC20 进行细胞分裂。相比之下，在许多细胞类型中为非必需蛋白的 fizzy-related-1（FZR1）被认为在后期细胞周期中在 APC 激活中发挥作用，尤其是在核内复制中。与此一致的是，Fzr1 基因敲除的小鼠胚胎显示出正常的着床前发育，但由于核内复制缺乏而死亡，这是胎盘形成所必需的。然而，由于存在母体储备，FZR1 在这一时期的作用的解释受到阻碍。因此，在这项研究中，我们使用卵母细胞特异性敲除来检查 FZR1 在早期小鼠胚胎发育中的功能。母体 FZR1 对于完成减数分裂并不是至关重要的，此外，Fzr1 基因敲除的雌性与正常雄性交配后也能生育出存活的幼仔。然而，在早期胚胎中，缺失母源和父源的 FZR1 会导致基因组完整性的急剧丧失，以至于大多数胚胎在仅经历一次有丝分裂分裂后就停止了，并且含有许多 γ-H2AX 焦点，这与断裂的 DNA 一致。这些胚胎的一个显著特征是在原核融合后建立了两个独立的纺锤体，因此染色体不能混合（合子）。这导致了双核 2 细胞胚胎的形成。在进展到 4 细胞阶段的 10%的胚胎中，分裂非常缓慢，导致致密化过早发生。从未观察到胚胎发育到胚泡阶段。我们的结论是，Fzr1 是一个非常重要的基因，参与了从 1 细胞胚胎的两个原核中建立一个纺锤体，以及在早期哺乳动物胚胎的有丝分裂过程中维持基因组完整性。
