Department of Cell and Developmental Biology, Center of Anatomy and Cell Biology, Medical University of Vienna, 1090, Vienna, Austria.
Department of Genetics, Stanford University, Stanford, CA, 94305, USA.
Histochem Cell Biol. 2021 Sep;156(3):197-207. doi: 10.1007/s00418-021-02008-6. Epub 2021 Jun 27.
Human preimplantation development is characterized by low developmental rates that are poorly understood. Early mammalian embryogenesis is characterized by a major phase of epigenetic reprogramming, which involves global DNA methylation changes and activity of TET enzymes; the importance of DNA methylation reprogramming for successful human preimplantation development has not been investigated. Here, we analyzed early human embryos for dynamic changes in 5-methylcytosine and its oxidized derivatives generated by TET enzymes. We observed that 5-methylcytosine and 5-hydroxymethylcytosine show similar, albeit less pronounced, asymmetry between the parental pronuclei of human zygotes relative to mouse zygotes. Notably, we detected low levels of 5-formylcytosine and 5-carboxylcytosine, with no apparent difference in maternal or paternal pronuclei of human zygotes. Analysis of later human preimplantation stages revealed a mosaic pattern of DNA 5C modifications similar to those of the mouse and other mammals. Strikingly, using noninvasive time-lapse imaging and well-defined cell cycle parameters, we analyzed normally and abnormally developing human four-cell embryos for global reprogramming of DNA methylation and detected lower 5-methylcytosine and 5-hydroxymethylcytosine levels in normal embryos compared to abnormal embryos. In conclusion, our results suggest that DNA methylation reprogramming is conserved in humans, with human-specific dynamics and extent. Furthermore, abnormalities in the four-cell-specific DNA methylome in early human embryogenesis are associated with abnormal development, highlighting an essential role of epigenetic reprogramming for successful human embryogenesis. Further research should identify the underlying genomic regions and cause of abnormal DNA methylation reprogramming in early human embryos.
人类胚胎着床前的发育速度较慢，其机制尚不清楚。早期哺乳动物胚胎发生的特点是表观遗传重编程的主要阶段，包括广泛的 DNA 甲基化变化和 TET 酶的活性；DNA 甲基化重编程对人类胚胎着床前发育成功的重要性尚未得到研究。在这里，我们分析了早期人类胚胎中 TET 酶产生的 5-甲基胞嘧啶及其氧化衍生物的动态变化。我们观察到，5-甲基胞嘧啶和 5-羟甲基胞嘧啶在人类受精卵的亲本原核之间表现出与小鼠受精卵相似但程度较低的不对称性。值得注意的是，我们检测到低水平的 5-甲酰基胞嘧啶和 5-羧基胞嘧啶，而人类受精卵的母源或父源原核中没有明显差异。对人类胚胎着床后早期阶段的分析显示，DNA 5C 修饰的镶嵌模式与小鼠和其他哺乳动物相似。引人注目的是，使用非侵入性的延时成像和明确的细胞周期参数，我们分析了正常和异常发育的人类四细胞胚胎的 DNA 甲基化整体重编程，并发现正常胚胎中的 5-甲基胞嘧啶和 5-羟甲基胞嘧啶水平低于异常胚胎。总之，我们的结果表明，DNA 甲基化重编程在人类中是保守的，具有人类特有的动力学和程度。此外，早期人类胚胎中四细胞特异性 DNA 甲基组异常与发育异常有关，强调了表观遗传重编程对人类胚胎发生成功的重要作用。进一步的研究应确定早期人类胚胎中异常 DNA 甲基化重编程的潜在基因组区域和原因。
