Departments of Developmental Biology, Washington University School of Medicine, 660 South Euclid Avenue, Saint Louis, MO 63110, USA.
Development. 2011 Jan;138(1):33-44. doi: 10.1242/dev.059824. Epub 2010 Nov 23.
Transient maintenance of a pluripotent embryonic cell population followed by the onset of multi-lineage commitment is a fundamental aspect of development. However, molecular regulation of this transition is not well characterized in vivo. Here, we demonstrate that the nuclear protein Geminin is required to restrain commitment and spatially restrict mesoderm, endoderm and non-neural ectoderm to their proper locations in the Xenopus embryo. We used microarray analyses to demonstrate that Geminin overexpression represses many genes associated with cell commitment and differentiation, while elevating expression levels of genes that maintain pluripotent early and immature neurectodermal cell states. We characterized the relationship of Geminin to cell signaling and found that Geminin broadly represses Activin-, FGF- and BMP-mediated cell commitment. Conversely, Geminin knockdown enhances commitment responses to growth factor signaling and causes ectopic mesodermal, endodermal and epidermal fate commitment in the embryo. We also characterized the functional relationship of Geminin with transcription factors that had similar activities and found that Geminin represses commitment independent of Oct 4 ortholog (Oct25/60) activities, but depends upon intact Polycomb repressor function. Consistent with this, chromatin immunoprecipitation assays directed at mesodermal genes demonstrate that Geminin promotes Polycomb binding and Polycomb-mediated repressive histone modifications, while inhibiting modifications associated with gene activation. This work defines Geminin as an essential regulator of the embryonic transition from pluripotency through early multi-lineage commitment, and demonstrates that functional cooperativity between Geminin and Polycomb contributes to this process.
胚胎细胞多能性的短暂维持，随后是多谱系的定向分化，这是发育的一个基本方面。然而，这种转变的分子调控在体内还没有很好地描述。在这里，我们证明了核蛋白 Geminin 是维持胚胎细胞定向分化的必需因子，并将中胚层、内胚层和非神经外胚层限制在其在 Xenopus 胚胎中的适当位置。我们使用微阵列分析证明 Geminin 过表达抑制了许多与细胞定向分化相关的基因，同时提高了维持多能性早期和不成熟神经外胚层细胞状态的基因的表达水平。我们研究了 Geminin 与细胞信号转导的关系，发现 Geminin 广泛抑制了 Activin、FGF 和 BMP 介导的细胞定向分化。相反，Geminin 的敲低增强了生长因子信号诱导的定向分化反应，并导致胚胎中异位中胚层、内胚层和表皮命运的定向分化。我们还研究了 Geminin 与具有相似活性的转录因子的功能关系，发现 Geminin 的抑制作用独立于 Oct 4 同源物（Oct25/60）的活性，而依赖于完整的 Polycomb 抑制因子功能。与之一致的是，针对中胚层基因的染色质免疫沉淀分析表明，Geminin 促进 Polycomb 结合和 Polycomb 介导的抑制性组蛋白修饰，同时抑制与基因激活相关的修饰。这项工作将 Geminin 定义为胚胎从多能性向早期多谱系定向分化转变的重要调节因子，并表明 Geminin 和 Polycomb 之间的功能协同作用有助于这一过程。
