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

项目摘要 全局转录沉默是一个高度保守的进化事件，对于从转录水平向转录水平的转变至关重要。 从完全分化的卵母细胞到全能胚胎。尽管它对所有人的发展都很重要， 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， 卵母细胞整体转录沉默依赖于mRNA衰变激活剂。卵母细胞特异性丢失 ZFP 36 L2-一种在富含AU的元件介导的mRNA中具有明确作用的RNA结合蛋白 衰变-防止卵母细胞经历全局转录沉默。ZFP 36 L2缺陷型卵母细胞 发育不全，成熟和受精缺陷导致完全雌性 不孕单细胞RNA-seq分析显示，ZFP 36 L2调节大量转录调节因子， 在染色质修饰和转录起始和延伸中起中心作用。这种失调 导致不能积累与沉默、有能力状态相关的组蛋白甲基化标记。我们 结果确定了卵母细胞mRNA衰变激活剂在转录下调中的关键作用， 激活子，导致组蛋白甲基化，全球转录沉默和能力，从 卵母细胞到胚胎这些发现有力地指出了一个模型，在该模型中，在细胞中的全局转录沉默。 卵母细胞是由mRNA衰变介导的。本提案的目标是通过以下方式揭示机制： ZFP 36 L2导致的mRNA衰减导致卵母细胞中的整体转录沉默， 这种独特的遗传模型系统提供的见解的优势，以调查ZFP 36 L2的作用， 依赖性染色质修饰对整体转录沉默和成功转换至关重要 从卵母细胞到胚胎为了确定mRNA衰变在导致全局转录中的作用， 沉默，我们将确定ZFP 36 L2在卵母细胞全基因组中的直接靶点，并测试ZFP 36 L2在卵母细胞全基因组中的作用。 这些因子在介导整体转录沉默和卵母细胞发育能力中起重要作用。我们将 确定ZFP 36 L2在染色质修饰中的作用，包括组蛋白H3和DNA甲基化， 测试这些修饰在卵母细胞中的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ZFP 36 L2依赖性染色质修饰是否起到维持全局 转录沉默在卵母细胞到胚胎的过渡和/或设置激活新的阶段， 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.