Illuminating molecular mechanisms required for efficient reprogramming and transdiffrentiation

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Our bodies are made up of around 300 different types of cells, each with a different, specialized role. However, we were not always composed of all these different cells. In an early human embryo, it is a ball of just 100-150 cells, all of which are completely unspecialized. At this stage, each cell can divide to produce any of the body's cells. This flexibility is called 'pluripotency'. As the embryo develops and the body takes shape, the cells divide repeatedly, gradually becoming more specialized and losing their flexibility. To make the cells stay pluripotent, we have to take them out of the early embryo and provide them with the particular conditions they need to keep dividing without specialization; making copies of themselves. Cells extracted from an early embryo and multiplied in a dish like this are called embryonic stem cells (ESCs). Given the right cues, they can generate any type of specialized cell in the body. Until recently, we thought that once cells were specialized it was not possible to change their character - to convert them from, say, skin cells into muscle cells. However, in 2006 a technology called reprogramming was developed, with which we can make ESC-like flexible cells from any cells in the body. These artificial flexible cells are called 'induced pluripotent stem cells (iPSCs)'. The discovery of iPSCs is a very exciting achievement because it allows us, in theory, to generate iPSCs from any individual and then use them to make new specialized cells that might be needed for studying or treating disease. Inspired by the discovery of iPSCs, researchers have since developed methods for converting one type of specialized cell directly into another, without first going through the ESC-like flexible stage. For example, it is now possible to convert skin cells directly into muscle cells or blood cells in the lab. How do we achieve these 'reprogramming' and 'cell conversion' processes, which do not happen under normal circumstances inside the body? The trick is to understand a set of important proteins found inside cells called 'master transcription factors'. Each different type of cell, whether it is a specialized cell or an embryonic stem cell, has a unique combination of master transcription factors. These master transcription factors determine what a cell is by controlling how the DNA inside the cell is used. To achieve reprogramming and cell conversion, researchers take the master transcription factors of the kind of cell they want to make, and put them into another type of cell. So, putting the master transcription factors normally found in ESCs into skin cells allows us to reprogram the skin cells into ESC-like cells (iPSCs), overwriting the original skin characteristics of the cells. Putting muscle master transcription factors into skin cells converts them from skin to muscle. The principal is simple but the strategy does not always work well. We often cannot overwrite the cells' original character at all, and when we can achieve conversion it may be with as little as 0.1% efficiency.One of the possible reasons for the low efficiency of these conversion methods is that the master transcription factors cannot work alone. They often need other proteins to support them. In our preliminary experiments, we have identified a protein that we think boosts the master transcription factors to generate iPSCs more efficiently from skin cells. Excitingly, previously published studies suggest this protein could be a general booster for other master transcription factors, including those used for skin-to-muscle or skin-to-blood-cell conversion. In this project we aim to work out in more detail how this booster factor acts in reprogramming and cell conversion. This study will help us to understand why simply putting the master transcription factors into the cells is not sufficient to achieve cell conversion in most cases, and will enable us to find strategies to improve the technology.