H3K9去甲基化酶Jmjd1c/Kdm3c在发育多能性的诱导和维持中的作用及机制研究

The change in the epigenetic state is the molecular basis for reprogramming of differentiated somatic cells to become pluripotent stem cells with the capacity to self-renew unlimitedly and to differentiate into all cell lineages, i.e. generation of induced pluripotent stem cell (iPSC). However, it is unclear how epigenetic regulators control the somatic cell reprogramming. Our preliminary study found that down regulation of the demethylase of lysine 9 in histone 3 (H3K9) Jmjd1c/Kdm3c during the generation of iPSCs led to the reduction of the reprogramming efficiency; silencing of this demethylase in ESCs resulted in the differentiation of ESCs, accompanied by the elevation in the cellular level of H3K9 methylation. The finding implicates that Jmjd1c/Kdm3c may play an important role in the establishment and maintenance of the pluripotency. Nevertheless, the molecular mechanism underlying the function of Jmjd1c/Kdm3c remains unfolded. In this project, we will further characterize the role of Jmjd1c/Kdm3c in somatic cell reprogramming systemically and elucidate the molecular basis of the function through searching for the downstream targets of Jmjd1c/Kdm3c and the protein complexes containing Jmjd1c/Kdm3c, particularly its interaction with other histone demethylases, during reprogramming. The study will provide new insights into how pluripotency is established and maintained, paving road for the improvement of reprogramming efficiency.

体细胞重编程成为具有无限自我更新和多向分化潜能的多能干细胞，即建立iPSC的分子基础是细胞表观遗传状态的变化。但是，关于表观遗传调控是如何决定体细胞重编程还有许多问题待回答。我们发现，在iPSC建立过程中沉默表观遗传调控因子—H3K9去甲基化酶Jmjd1c/Kdm3c 的表达导致重编程效率降低；在ESC中下调Jmjd1c的表达使ESC发生分化，同时伴有细胞整体水平的H3K9甲基化修饰升高。这提示Jmjd1c可能对发育多能性的建立及维持是必需的。但是，Jmjd1c发挥这些作用的分子机制尚不清楚。在本项目中，我们拟在系统确定Jmjd1c在重编程中作用的基础上，通过寻找Jmjd1c在重编程中的下游基因及相互作用蛋白，尤其是与其它组蛋白去甲基化酶的相互作用，揭示Jmjd1c在发育多能性的建立与维持中作用的分子机制。该项目的完成将为明确发育多能性的建立与维持提供新视角，并为提高重编程的效率奠定基础。

组蛋白去甲基化酶在发育多能性的建立和维持中发挥着关键作用，但在这些过程中具有重要作用的组蛋白去甲基化酶并没有被全部鉴定出来，而且组蛋白去甲基化酶在此过程中发挥作用机制仍不是十分清楚。因此，我们在本项目中集中研究了H3K9去甲基化酶在发育多能性的建立与维持中的作用机制，鉴定出H3K9去甲基化酶Jmjd1c在维持小鼠胚胎干细胞自我更新以及体细胞重编程中发挥着重要作用。在小鼠胚胎干细胞中，干扰Jmjd1c的表达会激活MAPK/Erk信号通路和上皮-间充质转变（EMT），进而诱导小鼠胚胎干细胞发生分化。机制上，Jmjd1c通过维持miR-200和miR-290/295家族启动子区域H3K9me2低甲基化修饰来促进miR-200和miR-290/295的表达，而miR-200和miR-290/295家族可以通过抑制MAPK/Erk信号通路和EMT来维持小鼠胚胎干细胞的自我更新和发育多能性。此外，在体细胞重编程过程中，干扰或者敲除Jmjd1c的表达将显著降低重编程效率，而过表达miR-200家族则可以部分地恢复Jmjd1c-null MEF的重编程效率。综上，我们首次揭示了H3K9去甲基化酶Jmjd1c通过调控miR-200和miR-290/295家族的表达来抑制MAPK/Erk信号通路激活和EMT发生，进而促进胚胎干细胞自我更新以及发育多能性的维持和建立。

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