Model-based analysis of spatio-temporal heterogeneity of mouse embryonic stem cells with respect to its functional role in regulating pluripotency

小鼠胚胎干（mES）细胞在多种不同细胞类型（多能性）中具有自我更新和分化的潜力。然而，关于多能性和mES细胞空间组织的分子调控的许多细节仍然未知。特别有趣的是，不同类型的异质性似乎对多能性的维持和调节起着功能作用。作为一个突出的例子，关键转录因子Nanog已经证明，维持多能性最终并不需要持续的高表达水平，而且表达水平实际上是可变的和可逆的变化。在拟议的项目中，我们将开发mES细胞组织的定量数学模型，以解决异质性是否以及（如果是的话）如何作为维持多能性的功能因素的问题。在此，我们将使用不同的mES细胞系的实验策略与多级数学建模方法相结合，该方法描述了从转录因子网络到空间扩展细胞群水平的mES细胞组织。这种方法允许研究异质性在细胞内和细胞间水平上的功能作用，并推导出多能状态如何进入、维持和退出的预测。由此产生的定量模型将有助于对mES细胞行为的全面、系统的理解，这对于在靶向分化或重编程的背景下干扰和控制（干细胞）的命运是最终必要的。建议的项目分为两部分。第一部分侧重于mES细胞的细胞内动力学以及与关键转录因子如Nanog和Rex1的表达有关的群体固有异质性的产生。该项目的第二部分扩展了建模方法，以纳入不同培养条件下mES细胞的空间组织和空间异质性的动态。

Mouse embryonic stem (mES) cells are well characterized with respect to their potential for selfrenewal and differentiation in a multitude of different cell types (pluripotency). However, many details about the molecular regulation of pluripotency and the spatial organization of mES cells are still unknown. It is particularly intriguing that different types of heterogeneity seem to play a functional role for the maintenance and regulation of pluripotency. As a prominent example it has been demonstrated for the key transcription factor Nanog that continuously high expression levels are not ultimately required to maintain pluripotency and that the expression levels are in fact variable and reversibly changing. Within the proposed project we will develop a quantitative mathematical models of mES cell organization to address the question if and (if yes) how heterogeneity acts as a functional element for the maintenance of pluripotency. Herein we will combine experimental strategies using different mES cell lines with a multi-level mathematical modelling approach describing mES cell organization from transcription factor networks up to the level of spatially extended cell populations. This approach allows studying the functional role of heterogeneity on the intra- and inter-cellular level, and to derive predictions on how the pluripotent state can be entered, maintained, and exited. The resulting, quantitative models will contribute a comprehensive, systemic understanding of mES cell behaviour, which is ultimately necessary to interfere and to control the fate of (stem) cells in the context of targeted differentiation or reprogramming. The suggested project is divided into two parts. Part I focuses on the intra-cellular dynamics of mES cells and the generation of population inherent heterogeneity with respect to the expression of crucial transcription factors such as Nanog and Rex1. Part II of the project extends the modelling approach to incorporate the dynamics of spatial organization and spatial heterogeneity of mES cells under different culture conditions.