The Role of Nanog in Establishment and Patterning of Embryonic Pluripotency

胚胎干细胞（ES）可以变成体内的任何细胞，因此它们作为再生医学工具修复因损伤或疾病而受损的组织具有很大的潜力。因此，现代医学的一个主要目标是了解如何为治疗目的获取胚胎干细胞的潜力。胚胎干细胞成为其他细胞的标志性能力被称为多能性，它受到蛋白质因子（称为多能性因子）的精心调节，这些蛋白质因子控制着调节胚胎干细胞行为的基因。我们正在努力确定这些基因是如何被控制的，我们把重点放在了一个最重要的多能性因子上，它被称为Nanog，是干细胞行为的主要调节器。胚胎干细胞类似于构成早期胚胎的细胞，因此，通过了解胚胎如何发育，就有可能了解如何调节胚胎干细胞，使其成为特定类型的成人细胞。然而，为了理解胚胎干细胞是如何成为多能性的，有必要考虑胚胎本身多能性的建立。然而，人类和其他哺乳动物的胚胎非常小，它们在母亲体内发育，所以很难接近和操纵。解决这个问题的一个方法是使用其他物种的胚胎，它们的细胞与人类胚胎相似，但更容易处理。这种方法已经在生物学中使用了几十年，用于鉴定胚胎细胞中基因的功能。然而，我们发现，大多数研究人员在实验室中使用的青蛙和鱼的胚胎不含多能细胞。出于这个原因，我们必须开发一种新的实验系统，使用蝾螈的胚胎。哺乳动物是从两栖动物进化而来的，其中有两种，青蛙和蝾螈。这两种两栖动物最后一次有共同的亲缘关系是在2.5亿年前。从那以后，青蛙进化出了许多独特的特征，然而蝾螈从它们第一次在地球上行走以来就保持相对不变，它们进化成爬行动物和哺乳动物。因此，控制蝾螈和哺乳动物胚胎发育的基因几乎是相同的。事实上，蝾螈是蝾螈的代表，我们已经证明它们含有多能细胞，基本上与人类胚胎中的细胞相同。此外，重要的是，它们含有Nanog基因，由于尚不完全清楚的原因，这种基因不存在于青蛙胚胎中。就我们的目的而言，蝾螈胚胎是一个完美的工具，可以用来了解多能细胞是如何对指示它们变成其他细胞类型的信号做出反应的。我们正在使用美西螈胚胎来研究Nanog是如何被调节的。美西螈胚胎在母体外发育，因此可以在不伤害动物的情况下收集数百个胚胎。而且，这些胚胎非常巨大，大约是人类胚胎的一万倍大，所以很容易在实验室里解剖你想要研究的细胞。我们开发的蝾螈实验系统在英国是独一无二的，我们是目前世界上唯一一个使用它来了解多能性的团队。当我们从蝾螈中分离出Nanog基因时，我们发现它在控制胚胎干细胞行为方面和人类Nanog一样有效。但是胚胎干细胞不是胚胎，我们有一个独特的机会来了解Nanog在正常胚胎中是如何发挥作用的，一个蝾螈的胚胎。在这个项目中，我们将在美西螈胚胎中提取多能细胞，并使用含有控制正常胚胎发育的分子的溶液诱导它们成为特定类型的分化细胞。然后，我们将分析Nanog的缺失如何改变对这些信号的反应。通过确定细胞如何反应，我们将了解建立多能性的必要的第一步，这将为如何生产用于再生受损身体部位的人体组织提供线索。

Embryonic stem (ES) cells can become any cell in the body, and so they have great potential as a tool for regenerative medicine to repair tissue damaged by injury or disease. A major goal of modern medicine, therefore, is to understand how to harvest the potential of embryonic stem cells for therapeutic purposes. The signature ability of ES cells to become other cells is called pluripotency, which is carefully regulated by protein factors, called pluripotency factors, which control the genes that regulate ES cell behaviour. We are working to identify how those genes are controlled, and we have focused on one of the most important pluripotency factors, called Nanog, a master regulator of stem cell behaviour.ES cells resemble the cells that make up early embryos, and so by understanding how embryos develop it becomes it is possible to learn how to regulate ES cells to make specific types of adult cells. However, to understand how ES cells become pluripotent, it is necessary to consider the establishment of pluripotency in the embryo itself. However, the embryos of humans, and other mammals, are very small, and they develop inside the mother, so they are very difficult to access and to manipulate. A way around this problem is use the embryos of other species, whose cells resemble those of human embryos, but which are much easier to work with. This approach has been used for decades in biology to identify the function of genes in embryonic cells. However, we discovered that the embryos of frogs and fish, which most investigators use in the lab, do not contain pluripotent cells. For this reason we had to develop a novel experimental system using embryos from axolotls.Mammals evolved from amphibians, of which there are two types, frogs and salamanders. These two types of amphibians last had a common relative 250 million years ago. Since then, frogs have evolved many traits are unique to them, however salamanders have remained relatively unchanged since they first walked the earth, and they evolved into reptiles and mammals. For this reason, the genes that control the development of embryos from salamanders and mammals are almost the same. In fact, axolotls are representative salamanders, and we have shown that they contain pluripotent cells that are basically the same as the ones that develop in human embryos. Also, importantly, they contain a Nanog gene, which for reasons that are not entirely clear, does not exist in frog embryos. For our purposes axolotl embryos are a perfect tool to understand how pluripotent cells respond to signals that tell them to become other cell types. We are using axolotl embryos to study how Nanog is regulated.Axolotl embryos develop outside of the mother, so hundreds of embryos can be collected without harming the animals. Also, the embryos are enormous, about 10,000 times the size of human embryos, so it is very easy to dissect the cells you want to study in the lab. The axolotl experimental system that we developed is unique in the UK, and we are the only group in the world currently using it to understand pluripotency. When we isolated the Nanog gene from axolotls we showed that it works as well as human Nanog in controlling the behaviour of ES cells. But ES cells are not embryos, and we have the unique opportunity to understand how Nanog functions in a normal embryo, the embryo of an axolotl.In this project we will take the pluripotent cells in axolotl embryos and induce them to become specific types of differentiated cells using solutions that contain the molecules that control development of normal embryos. We will then analyse how the loss of Nanog changes the response to these signals. By identifying how the cells respond we will understand the necessary first step in the establishment of pluripotency, and this will provide cues for how to produce human tissue for regenerating damaged body parts.