1. Institute of Diabetes and Regeneration Research, Helmholtz Zentrum München, D-85764 Neuherberg, Germany
2. Institute of Stem Cell Research, Helmholtz Zentrum München, D-85764 Neuherberg, Germany
3. German Center for Diabetes Research (DZD), D-85764 Neuherberg, Germany
4. Technical University of Munich, Medical Faculty, 81675 Munich, Germany