Until now, stem cell researchers believed it to be impossible for cells originating in one cellular layer to cross the boundaries to the other two cellular layers found in a developing embryo. These three layers, also known as germ layers, are the endoderm, the ectoderm and the mesoderm. From these, certain organs and tissues can develop. This means that a cell meant to become the liver could never become skin.Now a team of scientists from the University of Edinburgh's Medical Research Council Centre for Regenerative Medicine and The Ecole Polytechnique FÃ©dÃ©rale de Lausanne in Switzerland have reprogrammed cells from the thymus, an organ of the immune system, into hair follicle stem cells. These are the origin of follicle cells responsible for producing hair.This was done without the manipulation of the cell's genome. The researchers grew the rat thymus cells under the conditions required for the development of follicle cells. Afterwards, those gained cells were transplanted into developing skin, repairing it for more than a year and even becoming more genetically similar to follicle cells. Compared to the normal cells, which are functional for three weeks only, they performed far better.The research shows that the influence of a surrounding environment can reprogramme a stem cell, so that it is doing a job which it normally could not. In this case, the thymus cells from the endoderm turned into skin tissue that would normally originate from the ectoderm. These results suggest that the borders between the germ layers are not as strict as previously thought.Professor Yann Barrandon from the Ecole Polytechnique who was leading the project, said: "These cells change because of the environment they come into contact with, the skin. In theory this operation could be recreated with other organs as well."This research was supported by EU Sixth Framework project EuroStemCell and continued under the FP7 projects EuroSyStem and OptiStem. It is published in Nature.