Sox transcription factor function and redundancy in the central nervous system

在复杂的多细胞生物（如人类）的早期发育过程中，细胞必须采用特定的命运，以产生构建胚胎所需的各种组织和器官。在发育早期，特定的细胞组获得了随后发展成神经系统各种细胞类型的能力。一旦被指定，这种细胞群将在未分化状态下分裂，即神经干细胞，产生足够的细胞，这些细胞随后可以被引导形成神经元和其他类型的细胞，这些细胞是构建神经系统所必需的。这些神经干细胞不仅对正常发育很重要，而且还可以从其他类型的细胞中分离或产生并在实验室中培养。人们希望，神经干细胞将在未来为目前难以治疗的人类神经系统疾病提供一条治疗途径。支持细胞做出发育选择和维持干细胞状态的是一组被称为转录因子（tf）的蛋白质，它们在细胞核中起作用，控制决定神经状态的特定基因组。其中一类在神经干细胞中很重要的tf被称为Sox蛋白。虽然已经有相当多的工作旨在解决Sox蛋白如何控制哺乳动物干细胞状态，但由于三种密切相关的蛋白同时存在于神经细胞中，并且在发生突变时相互补偿，这一事实使这项工作变得复杂。这使得很难理解这些蛋白质的功能，这是一个重要的问题，因为它们在干细胞生物学中起着至关重要的作用。果蝇（Drosophila melanogaster）是实验室中广泛用于研究复杂多细胞动物遗传和发育基本方面的模型系统。一般来说，果蝇为研究基本生物过程提供了一个简单得多的系统，因为它易于维护，易于基因操作，并且不会引起对实验工作中过度使用动物的担忧。多年来，人们已经确定，苍蝇细胞做出的许多细胞命运选择是由一组调节蛋白控制的，这些调节蛋白与哺乳动物的蛋白质有着非常密切的关系，它们发挥着类似的作用。就Sox蛋白在神经系统中的作用而言，我们已经表明，果蝇提供了一个更简单的实验系统，它仍然具有哺乳动物蛋白质所显示的一些复杂性。而不是三个Sox蛋白，苍蝇只有两个，我们已经证明，小鼠和人类的Sox蛋白能够有效地在苍蝇中发挥作用。Sox蛋白通过控制一组定义细胞表型的基因发挥作用，我们最近的工作表明，果蝇和小鼠神经干细胞中的Sox蛋白控制着许多相同的基因。然而，尽管对哺乳动物和果蝇的Sox蛋白进行了大量的研究，但我们对它们如何调节靶基因的机制理解仍然很差。如果我们要在实验室中生成和操作用于治疗用途的神经干细胞，那么充分了解Sox蛋白所起的作用是很重要的，特别是因为它们现在经常用于产生和维持干细胞。我们将在果蝇模型中对果蝇和哺乳动物的Sox蛋白进行详细分析，以更全面地了解它们如何识别它们在细胞核中控制的特定基因，相关的Sox蛋白如何协同作用并能够相互弥补损失，并探索为什么重要的细胞类型（如神经干细胞）需要表达密切相关的Sox蛋白。虽然我们的工作是在苍蝇身上进行的，但事实上，Sox在苍蝇和老鼠身上的功能是如此相似，这意味着我们所了解的将与人类生物学相关。

During the early development of complex multicellular organisms such as humans, cells must adopt particular fates in order to generate the variety of tissues and organs necessary to build the embryo. Early in development, specific sets of cells gain the ability to subsequently develop the various cell types of the nervous system. Once specified, this cell population will divide in an undifferentiated state, known as neural stem cells, to generate sufficient cells that can subsequently be directed to make neurons and other cell types necessary to build a nervous system. Not only are these neural stem cells important for normal development, they may also be isolated or generated from other cell types and grown in the laboratory. It is hoped that neural stem cells will in the future provide a route for the treatment of human neurological disorders that are currently intractable. Underpinning the developmental choices cells make and their maintenance of the stem cell state are sets of proteins known as transcription factors (TFs) that act in the cell nucleus to control the specific sets of genes that define the neural state. One such class of TFs important in neural stem cells are known as Sox proteins. While there has been considerable work aimed at addressing how Sox proteins act to control the stem cell state in mammals, this work is complicated by the fact that three closely related proteins are present in neural cells at the same time and compensate for each other when mutations are made. This makes it difficult to understand how these proteins function and this is an important issue since they play such a crucial role in stem cell biology.The fruit fly, Drosophila melanogaster, is a model system widely used in the laboratory to study basic aspects of the genetics and development of complex multicellular animals. In general, the fly offers a much simpler system for studying basic biological processes since it is easy to maintain, easy to manipulate genetically and does not raise concerns about excessive animal use in experimental work. Over the years it has been established that many of the cell fate choices fly cells make are governed by sets of regulatory proteins that are very closely related to mammalian proteins performing similar roles. In the case of Sox proteins acting in the nervous system, we have shown the fly offers a simpler experimental system that still shares some of the complexity shown by mammalian proteins. Instead of three Sox proteins, the fly has only two, and we have shown that mouse and human Sox proteins are able to efficiently function in the fly.Sox proteins function by controlling sets of genes that define the phenotype of a cell and our recent work has shown that Sox proteins in fly and mouse neural stem cells control many of the same genes. However, despite a considerable amount of work on both mammalian and fly Sox proteins we still have a very poor mechanistic understanding of how they act to regulate their target genes. If we are to generate and manipulate neural stem cells in that lab for therapeutic uses, it is important we fully understand the roles Sox proteins play, particularly since they are now often used to produce and maintain stem cells. We will perform a detailed analysis of both fly and mammalian Sox proteins in the Drosophila model to understand more fully how they recognize the specific genes they control in the nucleus, how related Sox proteins act together and are able to compensate for each others loss and explore exactly why important cells types such as neural stem cells need to express closely related Sox proteins. Although our work is performed in the fly, the fact that Sox function is so similar in fly and mouse means that what we learn will be relevant to human biology.