Function of cell fate determinants during acquisition and loss of pluripotency

胚胎干细胞(ESCs)来源于哺乳动物胚泡的内细胞团，具有无限生长的能力，同时保持多能性和分化为所有三个生殖层细胞的能力。最近的开创性实验表明，通过表达四种选定的因子，可以从成体细胞中产生多能细胞。这些细胞被称为诱导多能干细胞(IPS)。有趣的是，除了知道哪些因素是实现重编程所必需的，还不太清楚是什么分子机制调节了体细胞到iPS细胞的“重编程能力”。此外，调节多能性退出的机制和分子也鲜为人知。因为重新编程到iPS细胞和退出多能性这两个过程都代表着细胞命运的变化，所以我们在这里提出了细胞命运决定因素是这些过程的重要调节因素的模型。因此，低水平的分化诱导细胞命运决定因素增加了细胞被重新编程为诱导多能干细胞(iPS细胞)的潜力。相比之下，多能性的退出可以通过上调这些决定因素来实现。我们计划通过研究细胞命运决定因子TRIM32在这些过程中的功能来详细解决这一假说。在这种情况下，我们选择研究TRIM32，因为它的表达模式，它对重编程因子c-Myc的已知直接调节，以及它对重编程因子Sox2，Nanog和Oct4的间接的，微RNA依赖的调节。该项目的成功完成将导致对调节进入和退出多能性的分子机制有更详细的了解。此外，该项目可能导致更有效地诱导多能细胞以及定向分化多能细胞。

Embryonic stem cells (ESCs), which are derived from the inner cell mass of mammalian blastocysts, have the ability to grow indefinitely while maintaining pluripotency and the ability to differentiate into cells of all three germ layers. Recent pioneering experiments have shown that by expressing four selected factors pluripotent cells can be generated from adult somatic cells. These cells are called induced pluripotent stem (iPS) cells. Interestingly, besides knowing which factors are necessary to achieve the reprogramming, it is rather unknown what molecular mechanisms regulate the “reprogrammability” of a somatic cell into an iPS cell. Furthermore, also the mechanisms and molecules that mediate the exit from pluripotency are poorly understood. Because both processes, reprogramming into iPS cells and exit from pluripotency, represent changes in cell fate we here propose the model that cell fate determinants are important regulators of these processes. Accordingly low levels of differentiation inducing cell fate determinants increase the potential of a cell to be reprogrammed into an induced pluripotent stem cell (iPS cell). In contrast the exit from pluripotency could be mediated by an upregulation of such determinants. We plan to address this hypothesis in detail by investigation of the function of the cell fate determinant TRIM32 during these processes. We have chosen to investigate TRIM32 in this context because of its expression pattern, its known direct regulation of the reprogramming factor c-Myc and its indirect, micro-RNA dependent regulation of the reprogramming factors Sox2, Nanog and Oct4. The successful completion of this project will lead to a more detailed understanding of the molecular mechanisms that regulate the entry and the exit into and from pluripotency. Additionally, this project could lead to methods to make induction of pluripotency as well as directed differentiation of pluripotent cells more efficient.