Predictive molecular features of developmental competence in mouse embryos bisected at the 2-cell stage

从2011年到2014年，我们在MPI和CeRA的两个小组联手研究了培养条件对辅助生殖技术（ART）小鼠模型胚胎质量的影响。出乎意料的是，在临床使用的培养基中切割后，受精的小鼠卵母细胞呈现出不同的发育轨迹，其特征是囊胚的中等特异性比例和中等特异性的基因表达模式。DFG的更新应用促进了对体外条件下胚胎发育的新理解，这与估计ART程序的任何潜在风险有关，也为预测ART程序的结果和减少卵母细胞的损失从而减少ART周期的数量提供了线索。我们的重点是培养基，因为它们可以在实验生物学的其他领域重新编程细胞的命运；那么，在ART方面呢？鉴于人类胚胎的异质性，到目前为止，很难区分受精后培养环境的贡献与配子内在质量的贡献（自然vs后天）。虽然在小鼠中模拟这种异质性是不切实际的，但几乎完全消除这种异质性是可行的。利用2细胞阶段小鼠胚胎对分的方法，我们可以在给定环境（培养基）的条件下，追求使2细胞胚胎成为发育者或非发育者的分子特征：对分后，一个细胞提供分子信息，与另一个细胞的发育信息相匹配。此外，我们可以使用这两个同卵双胞胎来测试两种不同的培养基是否会从相同的基因型中引发不同的发育轨迹。通过对不同培养基中生长的双胞胎胚胎转录组的生物信息学比较，我们将了解环境信号的分子转导（胚胎质量的外在调节剂，如信号通路）。通过对不同培养基中发育正常和发育不正常卵裂球转录组的比较，我们将了解对环境信号不太敏感的基因的核心。我们的工作可以推动胚胎研究向前发展，因为双胞胎模型将应用于ART培养基的研究，从而发现新的端点，为哺乳动物发育的早期阶段提供见解。与我们之前的DFG项目一样，本次更新申请将为植入前开发的关键步骤提供科学依据。此外，它应该有助于了解卵母细胞是否更适合在受精后但胚胎基因组激活之前在某种培养基中培养，而不是在另一种培养基中培养。MPI和CeRA之间的合作将产生有效的数据，以阐明哺乳动物生命中最早的个性特征。

From 2011 to 2014 our two groups at MPI and CeRA joined strengths to investigate the effects of culture conditions on embryo quality in the mouse model of assisted reproductive technologies (ART). Unexpectedly, upon cleavage in culture media that are used in the clinics, fertilized mouse oocytes took on different developmental trajectories, characterized by medium-specific proportions of blastocysts and medium-specific patterns of gene expression. This renewal application to the DFG fosters new understanding of embryo development under in vitro conditions which are relevant to estimate any potential risks of ART procedures, and also provides clues to anticipate the outcome of ART procedures and to minimize the loss of oocytes and thereby the number of ART cycles. Our focus is on culture media, because they can reprogram cell fate in other fields of experimental biology; so, what about in ART?Given the heterogeneity of human embryos, until now it proved difficult to distinguish the contribution of the postfertilization culture environment from that of the intrinsic quality of the gametes (nature vs nurture). While it is utopic to mimic such heterogeneity in mice, it is feasible to eliminate it almost completely. Taking advantage of the method of mouse embryo bisection at the 2-cell stage, we can pursue the molecular traits that make a 2-cell embryo a developer or a non-developer under the provisions of a given environment (medium): after bisection, one cell provides the molecular information, which can be matched with the developmental information of the other cell. Further, we can use the two monozygotic twins to test if two different media elicit different developmental trajectories from the same genotype. From the bioinformatic comparison of the transcriptomes of twin embryos grown in different media we shall learn about the molecular transductors of environmental cues (extrinsic modulators of embryo quality e.g. signaling pathways). From the comparison of the transcriptomes of developmentally competent vs incompetent blastomeres across culture media we shall learn about the core of genes that are less sensitive to environmental cues.Our work can bring embryo research forward as the model of twinning will be applied to the study of ART culture media, leading to discover novel endpoints providing insight into the earliest stages of mammalian development. As in our previous DFG project, this renewal application will provide scientific evidence for critical steps of preimplantation development. Also, it should help to understand whether oocytes would be more suited for culture in a certain medium as opposed to another medium, after fertilization but before embryonic genome activation. Our collaborative enterprise between MPI and CeRA shall generate valid data to illuminate the earliest features of individuality in mammalian life.