Recent studies have reported the differentiation of pluripotent cells into oocytes in vitro. However, the developmental competence of in vitro-generated oocytes remains low. Here, we perform a comprehensive comparison of mouse germ cell development in vitro over all culture steps versus in vivo with the goal to understand mechanisms underlying poor oocyte quality. We show that the in vitro differentiation of primordial germ cells to growing oocytes and subsequent follicle growth is critical for competence for preimplantation development. Systematic transcriptome analysis of single oocytes that were subjected to different culture steps identifies genes that are normally upregulated during oocyte growth to be susceptible for misregulation during in vitro oogenesis. Many misregulated genes are Polycomb targets. Deregulation of Polycomb repression is therefore a key cause and the earliest defect known in in vitro oocyte differentiation. Conversely, structurally normal in vitro-derived oocytes fail at zygotic genome activation and show abnormal acquisition of 5-hydroxymethylcytosine on maternal chromosomes. Our data identify epigenetic regulation at an early stage of oogenesis limiting developmental competence and suggest opportunities for future improvements.

中文翻译：

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表观遗传调控限制多能干细胞衍生卵母细胞的能力

最近的研究报道了多能细胞在体外分化为卵母细胞。然而，体外生成的卵母细胞的发育能力仍然很低。在这里，我们对所有培养步骤的小鼠生殖细胞体外发育与体内发育进行了全面比较，目的是了解卵母细胞质量差的机制。我们表明，原始生殖细胞在体外分化为生长中的卵母细胞以及随后的卵泡生长对于植入前发育的能力至关重要。对经历不同培养步骤的单个卵母细胞进行系统转录组分析，识别出在卵母细胞生长过程中通常上调的基因，这些基因在体外卵子发生过程中容易受到错误调节。许多失调的基因都是 Polycomb 的目标。因此，多梳抑制的失调是体外卵母细胞分化中已知的一个关键原因和最早的缺陷。相反，结构正常的体外衍生卵母细胞无法激活合子基因组，并显示母体染色体上 5-羟甲基胞嘧啶的异常获取。我们的数据确定了卵子发生早期的表观遗传调控限制了发育能力，并提出了未来改进的机会。