en Original Article Original Article Germline and somatic stem cells are distinct types of stem cells that are dedicated to reproduction and somatic tissue regeneration, respectively. Germline stem cells (GSCs), which can self-renew and generate gametes, are unique stem cells in that they are solely dedicated to transmit genetic information from generation to generation. We developed a strategy for the establishment of germline stem cell lines from embryonic stem cells (ES). These cells are able to undergo meiosis, generate haploid male gametes in vitro and are functional, as shown by fertilization after intra-cytoplasmic injection into mouse oocytes. In other approach, we show that bone marrow stem (BMS) cells are able to trans-differentiate into male germ cells. BMS cell-derived germ cells expressed the known molecular markers of primordial germ cells. The ability to derive male germ cells from ES and BMS cells reveals novel aspects of germ cell development and opens the possibilities for use of these cells in reproductive medicine. Conversely, we showed that adult male germline stem cells, spermatogonial stem cells (SSCs), can be converted into embryonic stem cell like cells which can differentiate into the somatic stem cells of three germ layers. Understanding how SSC can give rise to pluripotent stem cells and how somatic stem cells differentiate into germ cells could give significant insights into the regulation of developmental totipotency as well as having important implications for male fertility and regenerative medicine. Stem cells, Germ cells, Bone Marrow stem cells, Spermatognial stem cells 41 0 http://ijrm.ir/browse.php?a_code=A-10-549-275&slc_lang=en&sid=1 Karim Nayernia karim.nayernia@newcastle.ac.uk Yes North East Institute of Stem Cell Biology, Institute of Human Genetics, International Centre for Life, Central Parkway, University of Newcastle upon Tyne, UK Jae Ho Lee No North East Institute of Stem Cell Biology, Institute of Human Genetics, International Centre for Life, Central Parkway, University of Newcastle upon Tyne, UK Wolfgang Engel No Institute of Human Genetics, University of Goettingen, Germany Jessica Nolte No Institute of Human Genetics, University of Goettingen, Germany Nadja Drusenheimer No Institute of Human Genetics, University of Goettingen, Germany Kristina Rathsack No Institute of Human Genetics, University of Goettingen, Germany Arvind Dev No Institute of Human Genetics, University of Goettingen, Germany Gerald Wulf No Department of Haematology and Oncology, University of Göttingen, 37073 Göttingen, Germany Ingrid E Ehrmann No North East Institute of Stem Cell Biology, Institute of Human Genetics, International Centre for Life, Central Parkway, University of Newcastle upon Tyne, UK David Elliott No North East Institute of Stem Cell Biology, Institute of Human Genetics, International Centre for Life, Central Parkway, University of Newcastle upon Tyne, UK Ulrich Zechner No Institute of Human Genetics, University of Mainz, 51131 Mainz, Germany Thomas Haaf No Institute of Human Genetics, University of Mainz, 51131 Mainz, Germany Andreas Meinhardt No Department of Anatomy and Cell Biology, University of Giessen, 35378 Giessen, Department of Anatomy and Cell Biology, University of Giessen, 35378 Giessen, Germany Hans W Michelmann No Department of Obstetrics and Gynecology, University of Göttingen, 37073 Göttingen, Germany Gerlad Hasenfuss No Department of Cardiology, University of Goettingen, Germany Kaomei Guan No Department of Cardiology, University of Goettingen, Germany