The Role of Nanog in Establishment and Patterning of Embryonic Pluripotency

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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.