The zebrafish tectal stem cell niche - a new model for in vivo analysis of neural stem cell biology

胚胎后生物体中的干细胞调节生长、再生和修复。哺乳动物中两个最典型的例子是肠道干细胞，它们每隔几天更新一次肠道上皮，以及确保新血细胞稳定供应的造血干细胞。神经干细胞因其具有治疗前景而受到重视。理论上，这种细胞提供了再生受损神经组织的可能性，从而为神经退行性疾病（如阿尔茨海默病和帕金森病）和神经系统损伤提供了治疗方法。部分出于这个原因，人们正在努力识别和描述调节神经干细胞维持和分化的因素。哺乳动物的神经系统只包含有限数量的神经干细胞，而且这些干细胞存在于不易接近的壁龛中。因此，在活体动物的自然环境中研究这些细胞几乎是不可能的。与哺乳动物相比，其他脊椎动物，包括鱼类，有许多神经干细胞群，使它们成为很好的模型，可以补充哺乳动物和组织培养实验。本课题拟建立斑马鱼视顶盖作为研究神经干细胞生物学的新模型系统。视顶盖是鱼一生中生长和增加神经元的重要视觉中心。使这种生长成为可能的干细胞，有能力产生十几种顶状神经元类型，它们靠近大脑的表面。再加上斑马鱼胚胎的透明性，这些细胞可以在体内进行跟踪。相对而言，我们对神经干细胞和祖细胞在完整动物体内的行为知之甚少，我们的主要目标之一将是观察这些细胞的分裂、移动和分化。为了做到这一点，我们将使用复杂的转基因工具，使我们能够可视化细胞形状，跟踪细胞分裂并跟踪祖细胞产生神经元时的细胞运动。我们的第二个目标是描述影响神经干细胞生物学的信号。关于控制造血干细胞的信号，我们已经了解了很多，我们也发现了顶祖细胞和造血祖细胞之间令人惊讶的相似之处。Wnt通路在两个位置都被激活，我们将确定该通路如何影响顶状干细胞的维持、祖细胞的增殖和神经元的产生。其次，最近的数据表明前列腺素是造血系统生态位的新型关键调节因子。我们有初步的数据表明前列腺素可能在顶干生态位中具有保守的功能，并将探索这种可能性。这些研究将有助于确定调节干细胞的机制的保护程度，并将阐明神经干细胞生物学基础的信号机制。进一步的目标是解决眼睛和视神经顶盖之间的生长如何协调，我们将通过评估眼睛的顶盖神经支配如何调节干细胞和祖细胞的行为来解决这个问题。我们的工作的好处包括从完整动物的研究中更好地理解神经干细胞生物学。斑马鱼的透明性加上直肠干细胞的易获取性为在这种情况下研究神经干细胞提供了明显的优势。我们的研究将使其他研究不同干细胞模型的人受益，帮助设计实验和操纵干细胞用于治疗目的。调节干细胞的信号通路可以通过药物和/或基因操作来调节，这将为操纵干细胞提供途径。我们提出的研究还将建立一个新的模型系统来研究干细胞，我们希望其他研究人员能够利用这个模型系统。

Stem cells in post-embryonic organisms regulate growth, regeneration and repair. The two best-characterized examples in mammals are intestinal stem cells, which renew the gut epithelium every few days, and haematopoietic stem cells that ensure the steady supply of new blood cells. Neural stem cells have acquired prominence due to the therapeutic promise they carry. Theoretically, such cells provide the possibility to regenerate damaged neural tissue thereby providing treatment for neurodegenerative disorders (such as Alzheimer's and Parkinson's disease) and nervous system injuries. In part for this reason, significant efforts are being made to identify and characterise the factors that regulate the maintenance and differentiation of neural stem cells. The mammalian nervous system contains only limited populations of neural stem cells, and these reside in niches that are not easily accessible. It is therefore almost impossible to study such cells in their natural context of the living animal. In contrast to mammals, other vertebrates, including fish, have many populations of neural stem cells making them good models that can complement mammalian and tissue culture experiments. In this project, we propose to establish the zebrafish optic tectum as a new model system to study the biology of neural stem cells. The optic tectum is an important visual centre that grows and adds neurons throughout the life of the fish. The stem cells that make this growth possible, and that have the capacity to generate more than a dozen tectal neuron types, reside close to the superficial surface of the brain. Coupled with the transparency of the zebrafish embryo, these cells can be followed in vivo. Relatively little is known about the behaviour of neural stem cells and progenitors in the intact animal and one of our key goals will be to observe these cells as they divide, move and differentiate. To do this, we will use sophisticated transgenic tools that allow us to visualise cell shape, to follow cell divisions and to track cell movements as progenitor cells generate neurons. Our second goal is to characterise the signals that influence the biology of the neural stem cells. Much has been learned about the signals that control haematopoietic stem cells, and we have found some surprising similarities between tectal and haematopoietic progenitor cells. The Wnt pathway is activated in both locations and we will determine how this pathway influences the maintenance of tectal stem cells, the proliferation of progenitors and the production of neurons. Secondly, recent data has implicated prostaglandins as being novel, critical regulators of the haematopoietic stem niche. We have preliminary data that prostaglandins may have conserved function in the tectal stem niche and will explore this possibility. These studies will help to determine the extent of conservation of the mechanisms that regulate stem cells and will elucidate the signalling mechanisms that underlie neural stem cell biology.A further goal is to resolve how growth is coordinated between the eyes and the optic tectum and we will address this issue by assessing how tectal innervation by the eyes regulates stem cell and progenitor behaviour. The benefits from our work include a better understanding of neural stem cell biology drawn from studies in the intact animal. The transparency of the zebrafish coupled with the ease of accessibility of the tectal stem cells provides a clear advantage for studying neural stem cells in this context. Our research will benefit others working on different stem cell models in helping to design experiments and manipulate stem cells for therapeutic purposes. The signalling pathways that regulate stem cells can be modulated by drugs and/or genetic manipulation and this will provide routes to manipulate stem cells. The proposed research will also establish a new model system to study stem cells that we hope will be exploited by other researchers.