Understanding molecular mechanism and biological siginificance of dynamic fluctuation and heterogeneity of gene expression in ES cells and in the early mouse embryo

为了在干细胞研究方面取得进展，了解胚胎干细胞多能性的分子本质是至关重要的。虽然多能性一直被认为是一种特定细胞类型的静态状态，ES细胞是一个同质群体，但最近在小鼠ES细胞和早期胚胎中的发现表明，它实际上可能代表了异质群体动态平衡的某种条件。在未分化的ES细胞中，根据多潜能基因的表达确定了许多亚群。一直以来，在胚泡中发育成多能内细胞团(ICM)的小鼠胚胎细胞对谱系标记表现出高度的异质性和随机性的表达模式。本项目的主要目的是了解小鼠胚胎中多能ES细胞维持和ICM形成的独特原理。特别是，基因表达的动态时空变化将通过4D实时成像ES细胞培养和小鼠胚胎发育来充分表征。我们将重点研究Nanog和Stella基因，并研究表观遗传标记在基因表达变异调控中的作用。通过在平衡状态下操纵分子成分和表观遗传标记，将在ES细胞和小鼠胚胎中探索动态异质性的生物学意义。一个吸引人的假说是，这种动态的性质可能是多能性的一个基本特征，多能性状态的传播可能需要不同亚群的相互作用。在分子和系统水平上充分了解动态平衡将有助于洞察ES细胞的多能性维持。

For the progress in stem cell research, it is essential to understand the molecular nature of pluripotency in embryonic stem (ES) cells. While pluripotency has been assumed to be a “static” status of a particular cell type, with ES cells being a homogeneous population, recent findings in mouse ES cells and early embryos suggest that it may in fact represent a certain condition of dynamic equilibrium of heterogeneous populations. In undifferentiated ES cells, a number of subpopulations are identified in terms of expression of pluripotency genes. Consistently, mouse embryonic cells that develop to form the pluripotent inner cell mass (ICM) in blastocyst, exhibit highly heterogeneous, and presumably stochastic, expression pattern for the lineage markers.The primary aim of this project is to understand the unique principle underlying maintenance of the pluripotent ES cells and formation of the ICM in the mouse embryo. In particular, dynamic spatiotemporal change in gene expression will be fully characterized by 4D live-imaging ES cell culture and mouse embryonic development. We will focus on Nanog and Stella genes, and investigate the role of epigenetic markings in the regulation of gene expression variation. Biological significance of the dynamic heterogeneity will be explored in ES cells and in mouse embryos by manipulating the molecular components and epigenetic markings under equilibrium. An attractive hypothesis is that this dynamic nature may be an essential feature of pluripotency and interaction of distinct subpopulations may be required for propagation of the pluripotent status. Full understanding of the dynamic equilibrium at molecular and systems level will provide insight into pluripotency maintenance in ES cells.