Epigenetic dynamics of developing germ cells and early embryos

描述（由申请人提供）：哺乳动物的发育是由发育潜力的连续限制驱动的，因为全能性受精卵在成年动物体内产生了成熟细胞类型的多样性。动物体内的每个细胞所采用的特征是稳定的，并作为该细胞类型的长期记忆而携带。目前大多数模型表明，细胞记忆的机制是基因组的表观遗传修饰。在哺乳动物中，胞嘧啶核苷酸的甲基化，主要是在CG二核苷酸序列中，形成了一个无可争议的表观遗传标记，在每次细胞分裂中被复制。在生殖细胞的发育过程中，表观遗传标记在很大程度上被抹去，本质上是将基因组重置为全能状态的途径。受精后，DNA甲基化模式再次被重写。我们建议使用下一代DNA测序技术来绘制哺乳动物发育过程中表观遗传编程和重编程最动态阶段的DNA甲基化模式。我们将通过对长RNA和短RNA的分析，将这些与RNA表达模式联系起来。这项提议的目的是了解表观遗传标记的沉积是如何导致成年生物体内细胞类型多样性的产生的，以及这些标记本身是否预示着携带它们的细胞特征的变化。重要的是，我们将比较正常小鼠早期胚胎的表观遗传修饰模式与激素处理过排卵母亲早期胚胎的表观遗传特征。已经有迹象表明激素治疗可以改变一些基因的表观遗传状态。我们建议在全基因组范围内评估这些治疗的影响。这与人类健康高度相关，因为每年有多达100万妇女接受激素辅助受孕尝试。

DESCRIPTION (provided by applicant): Mammalian development is driven by the successive restriction of developmental potential as the totipotent zygote generates the diversity of mature cell types present within an adult animal. The characteristics adopted by each cell within the animal are stable and are carried as a long-term memory within that cell type. Most current models suggest that the mechanisms underlying cellular memory are epigenetic modifications of the genome. In mammals, methylation of cytosine nucleotides, mainly in CG dinucleotides sequences, forms an indisputable epigenetic mark that is copied at each cell division. During the development of germ cells, epigenetic marks are largely erased, essentially as a path toward resetting the genome to a totipotent state. After fertilization, the patterns of DNA methylation are again rewritten. We propose to use next-generation DNA sequencing technologies to map patterns of DNA methylation during the most dynamic phases of epigenetic programming and re-programming during mammalian development. We will correlate these with patterns of RNA expression through analyses of both long and short RNAs. The goal of this proposal is to understand how the deposition of epigenetic marks leads to the creation of the diversity of cell types within an adult organism and whether those marks themselves presage changes in the characteristics of cells that harbor them. Importantly, we will compare patterns of epigenetic modifications in early embryos derived from normal mice to epigenetic profiles of early embryos in hormone-treated, superovulated mothers. There are already indications that hormone treatment can alter the epigenetic state of some genes. We propose to evaluate the impact of such treatments on a genome-wide scale. This is highly relevant to human health since as many as 1 million women undergo hormone-assisted attempts at conception each year. PUBLIC HEALTH RELEVANCE: The inherited characteristics of any mammalian cell depend both upon the content of its genomic sequence and on epigenetic marks that modify the activity of genomically encoded programs. These epigenetic marks are highly dynamic during the production of germ cells and as the cells of an early embryo begin to specialize and follow particular developmental pathways. We will examine how the patterns of epigenetic marks are erased and rewritten during germ cell development and early embryogenesis, and compare the patterns of these marks in normally conceived embryos to those seen in embryos generated via hormone-assisted reproduction. These studies will both provide important basic biological insights and shed light on possible impacts of fertility treatments that are given to as many as a million women each year.