Mechanisms driving the transition from oocyte to embryo: The role of the mRNA decay activator ZFP36L2

项目总结 全球转录沉默是一种高度保守的进化事件，对于从 将完全分化的卵母细胞转化为全能胚胎。尽管它在所有国家的发展中都很重要 动物，这一关键的全基因组事件仍然知之甚少。我们最近发现， 卵母细胞的整体转录沉默依赖于一种mRNA衰变激活剂。卵母细胞特异性丢失 Zfp36l2--一种在富AU元件介导的mRNA中具有广泛作用的RNA结合蛋白 腐烂--防止卵母细胞经历整体转录沉默。Zfp36l2缺陷的卵母细胞 发育不全，在成熟和受精方面有缺陷，导致完全雌性 不孕不育。单细胞rna-seq分析表明，Zfp36l2调控着一系列转录调控因子。 在染色质修饰、转录起始和延伸中起中心作用。这种监管失调 导致未能积累与沉默、有能力状态相关的组蛋白甲基化标记。我们的 结果明确了卵母细胞mRNA衰变激活剂在转录下调中的关键作用 激活剂，导致组蛋白甲基化，全球转录沉默和从 从卵母细胞到胚胎。这些发现有力地指出了一种模型，在该模型中， 卵母细胞是由信使核糖核酸衰变来调节的。这项建议的目标是既揭示机制(S)，又 哪种mRNA被Zfp36l2降解导致卵母细胞整体转录沉默 利用这一独特的遗传模型系统提供的洞察力来研究Zfp36l2- 依赖染色质修饰对整体转录沉默和成功过渡至关重要 从卵母细胞到胚胎。确定信使核糖核酸衰变在导致整体转录中的作用 沉默，我们将在全基因组范围内确定Zfp36l2的直接靶点，并测试Zfp36l2在卵母细胞基因组中的作用 这些因素在调节整体转录沉默和卵母细胞发育能力中起作用。我们会 确定Zfp36l2在染色质修饰中的作用，包括组蛋白H3和DNA甲基化，以及 测试这些修饰在卵母细胞整体转录沉默中的作用。最后，我们将测试 在卵母细胞中建立的依赖于Zfp36l2的染色质修饰是否起到维持整体 在卵母细胞到胚胎的转变过程中转录沉默和/或为激活新的 在新形成的胚胎中转录。

PROJECT SUMMARY Global transcriptional silencing is a highly conserved evolutionary event central to the transition from the fully differentiated oocyte to the totipotent embryo. Despite its importance in the development of all animals, this pivotal genome-wide event remains poorly understood. We have recently discovered that oocyte global transcriptional silencing depends on an mRNA decay activator. Oocyte-specific loss of ZFP36L2—an RNA-binding protein with a well-established role in AU-rich element-mediated mRNA decay—prevents oocytes from undergoing global transcriptional silencing. ZFP36L2-deficient oocytes are developmentally incompetent, with defects in maturation and fertilization leading to complete female infertility. Single cell RNA-seq analysis revealed that ZFP36L2 regulates scores of transcription regulators with central roles in chromatin modification and transcription initiation and elongation. This dysregulation resulted in failure to accumulate histone methylation marks associated with the silent, competent state. Our results define a critical role for an oocyte mRNA decay activator in the downregulation of transcription activators, leading to histone methylation, global transcriptional silencing and competence to transition from oocyte to embryo. These findings strongly point to a model in which global transcriptional silencing in the oocyte is mediated by mRNA decay. The goals of this proposal are to both uncover the mechanism(s) by which mRNA decay by ZFP36L2 brings about global transcriptional silencing in the oocyte and to take advantage of the insights provided by this unique genetic model system to investigate the role of ZFP36L2- dependent chromatin modifications critical for global transcriptional silencing and the successful transition from oocyte to embryo. To determine the role of mRNA decay in bringing about global transcriptional silencing, we will identify the direct targets of ZFP36L2 in the oocyte genome-wide and test the role of these factors in mediating global transcriptional silencing and oocyte developmental competence. We will determine the role of ZFP36L2 in chromatin modification, including histone H3 and DNA methylation, and test the role of these modifications in global transcriptional silencing in the oocyte. Finally, we will test whether ZFP36L2-dependent chromatin modifications established in the oocyte act to maintain global transcriptional silencing over the oocyte-to-embryo transition and/or set the stage for activation of new transcription in the newly formed embryo.