Stem cell fate: exploiting the Drosophila germline to unravel the role of a conserved translation repression complex

干细胞不同于其他类型的细胞，因为它们可以分裂更新自己（即保持干细胞的状态），同时分化成具有不同身份的特化细胞。例如，胚胎干细胞可以在发育过程中形成所有不同的细胞、组织和器官，而有证据表明生殖系干细胞可以产生功能性的卵子和精子。鉴于这种独特的特性，干细胞有可能为神经退行性疾病和生育障碍等疾病提供新的治疗方法，并为修复受损组织（包括与心脏病和脊髓损伤相关的组织）提供新的策略，从而彻底改变医学。需要克服的主要障碍之一是在实验室中将干细胞诱导分化为多种不同的细胞类型。出现这种困难是因为干细胞决定自我更新或分化的机制尚不完全清楚。本提案中的研究旨在了解控制这一决策的机制之一。干细胞研究的首要模型之一是果蝇生殖系干细胞，因为对果蝇发育很重要的蛋白质与控制人类发育的蛋白质是一样的。此外，果蝇在短时间内适用于一系列实验方法，使其成为一种常用的研究模型，并且是一种道德争议较小的动物模型替代品。我们最近使用果蝇生殖系干细胞作为模型来研究干细胞选择保持干细胞或分化为特化细胞的决定基础。我们的工作集中在两种蛋白质上，称为Pumilio和Nanos，它们的功能是抑制生殖系干细胞的翻译（即蛋白质的合成）。我们已经在种系干细胞中发现了一种被Pumilio和Nanos抑制的mRNA，并表明这种mRNA的抑制缺失会导致干细胞分化而不是自我更新。有趣的是，在一项独立的研究中，mRNA编码的蛋白质最近被证明可以导致小鼠干细胞分化。这一结果表明，果蝇干细胞是鉴定促进小鼠和人类干细胞分化的重要因素的有力模型。本研究的目的是扩展我们对果蝇生殖系干细胞中翻译抑制因子的研究。我们将鉴定其他被Pumilio和Nanos抑制的mrna，并研究这些mrna是如何被选择的。然后，我们将测试在种系干细胞中失去这种抑制如何影响其自我更新或分化的决定。在人类干细胞中，Pumilio和Nanos在控制干细胞命运决定中也起着重要作用。因此，预计我们的研究结果将与其他类型的人类干细胞相关，并在长期内有助于在实验室环境中促进干细胞向特定细胞类型的分化，以便充分利用干细胞的治疗潜力。

Stem cells are different from other types of cells as they can divide to renew themselves (ie remain as a stem cell) and simultaneously differentiate into specialised cells with distinct identities. For example, embryonic stem cells can form all of the different cells, tissues and organs during development, whereas there is evidence that germline stem cells can give rise to functional eggs and sperm. Given this unique property, stem cells have the potential to revolutionise medicine by providing both new treatments for diseases such as neurodegenerative and fertility disorders, and novel strategies for repair of damaged tissue, including those associated with heart disease and spinal injury. One of the primary hurdles to be overcome is the induction of stem cell differentiation into multiple different cell types within the laboratory. This difficulty arises because the mechanisms underlying a stem cell's decision to renew itself or differentiate are not fully understood. The research in this proposal aims to understand one of the mechanisms that controls this decision. One of the premier models for stem cell research is fruitfly germline stem cells, as the proteins which are important for development of the fruitfly are the same as those which control development in humans. In addition, the fruitfly is amenable to a whole range of experimental approaches on a rapid timescale, making it a commonly used research model, and one that is a less morally contentious alternative to animal models. We have recently used fruitfly germline stem cells as a model to investigate the basis of the decision by which stem cells choose to either remain a stem cell or differentiate into specialised cells. Our work has focused on two proteins, called Pumilio and Nanos, which function to repress translation (ie the synthesis of proteins) in germline stem cells. We have identified a specific mRNA that is repressed by Pumilio and Nanos in germline stem cells, and shown that loss of repression of this mRNA causes the stem cell to differentiate rather than renew itself. Interestingly, the protein encoded by the mRNA has, in a separate study, recently been shown to cause mouse stem cells to differentiate. This result demonstrates that fruitfly stem cells are a powerful model for identifying factors important for promoting differentiation of mouse and human stem cells. The aim of this proposal is to extend our study of the translation repressors which function in fruitfly germline stem cells. We will identify other mRNAs that are repressed by Pumilio and Nanos, and investigate how these mRNAs are selected. We will then test how loss of this repression in a germline stem cell influences its decision to either renew itself or differentiate. Pumilio and Nanos also have important roles in controlling the stem cell fate decision in human stem cells. Therefore, it is anticipated that results from our study will be relevant to other types of human stem cells and in the longer term be useful for promoting stem cell differentiation into specific cell types within the laboratory setting, in order that the full therapeutic potential of stem cells can be harnessed.