Embryonic Stem (ES) cells possess a high capacity for self-renewal, expansion, lineage differentiation and manipulation in vitro. These pluripotent stem cells provide a most powerful system and serve as an exceptional resource for research into how stem cells development and how they make decisions to self-renew or differentiation. Dr. Raymond Poot studies the protein–interaction network in the differerentiation of ES cells towards the neuronal lineage. Dr. Joost Gribnau also uses ES cells to better understanding the process of X-chromosome inactivation. Along with ES cells he is interested in using iPS cells from patient material for these studies. About three years ago, a most remarkable discovery was made by the group of Yamanaka, in which highly differentiated somatic cells were able to be reprogrammed to a pluripotent stage by forced expression of four factors known to be important in ES cell pluripotency. The reprogrammed somatic cells became known as induced Pluripotental Stem (iPS) cells. The ability to make patient (disease carrying) specific iPS cells holds great potential for translational research by providing in vitro lineage differentiation model systems for study of the onset of human disease. To serve the research needs of the Erasmus MC research community, Dr. Gribnau has secured funds from the ESI Open call program to organize a core facility for the generation of patient specific iPS cells and to optimize the pluripotency of human ES cells and iPS cells, as potent as mouse ES cells. Specific optimization protocols are under study by Dr. Derk ten Berge who is examining the impact of Wnts on the maintenance of ES cell pluripotency and the effects of Wnt on epiblast stem cells.