Well-orchestrated epigenetic modifications during early development are essential for embryonic survival and postnatal growth. Erroneous epigenetic modifications due to environmental perturbations such as manipulation and culture of embryos during in vitro fertilization (IVF) are linked to various short- or long-term consequences. Among these, DNA methylation defects are of great concern. Despite the critical role of DNA methylation in determining embryonic development potential, the mechanisms underlying IVF-associated DNA methylation defects, however, remains largely elusive. We reported herein that repression of fibroblast growth factor (FGF) signaling as the main reason for IVF-associated DNA methylation defects. Comparative methylome analysis by postimplantation stage suggested that IVF mouse embryos undergo impaired de novo DNA methylation during implantation stage. Further analyses indicated that Dnmt3b, the main de novo DNA methyltransferase, was consistently inhibited during the transition from the blastocyst to postimplantation stage (Embryonic day 7.5, E7.5). Using blastocysts and embryonic stem cells (ESCs) as the model, we showed repression of FGF signaling is responsible for Dnmt3b inhibition and global hypomethylation during early development, and MEK/ERK-SP1 pathway plays an essential mediating role in FGF signaling-induced transcriptional activation of Dnmt3b. Supplementation of FGF2, which was exclusively produced in the maternal oviduct, into embryo culture medium significantly rescued Dnmt3b inhibition. Our study, using mouse embryos as the model, not only identifies FGF signaling as the main target for correcting IVF-associated epigenetic errors, but also highlights the importance of oviductal paracrine factors in supporting early embryonic development and improving in vitro culture system.

中文翻译：

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在体外受精胚胎的早期发育过程中，抑制 FGF 信号是导致 Dnmt3b 抑制和从头 DNA 甲基化受损的原因

在早期发育过程中精心策划的表观遗传修饰对于胚胎存活和出生后生长至关重要。由于环境扰动（例如体外胚胎的操作和培养）导致的错误表观遗传修饰受精（IVF）与各种短期或长期后果有关。其中，DNA甲基化缺陷备受关注。尽管 DNA 甲基化在确定胚胎发育潜力中起关键作用，但 IVF 相关 DNA 甲基化缺陷的潜在机制在很大程度上仍然难以捉摸。我们在此报道了成纤维细胞生长因子 (FGF) 信号传导的抑制是 IVF 相关 DNA 甲基化缺陷的主要原因。植入后阶段的比较甲基化组分析表明，IVF 小鼠胚胎在植入阶段经历了受损的从头DNA 甲基化。进一步的分析表明Dnmt3b是主要的de novoDNA 甲基转移酶在从胚泡到植入后阶段（胚胎第 7.5 天，E7.5）的过渡期间一直受到抑制。以囊胚和胚胎干细胞 (ESCs) 为模型，我们发现 FGF 信号传导的抑制是早期发育过程中Dnmt3b抑制和整体低甲基化的原因，而 MEK/ERK-SP1 通路在 FGF 信号传导诱导的转录激活中起重要的中介作用Dnmt3b。将仅在母体输卵管中产生的 FGF2 补充到胚胎培养基中显着挽救了Dnmt3b抑制。我们的研究以小鼠胚胎为模型，不仅将 FGF 信号确定为纠正 IVF 相关表观遗传错误的主要目标，而且强调了输卵管旁分泌因子在支持早期胚胎发育和改善体外培养系统中的重要性。