Department of Molecular Medicine, Institute of Basic Medical Sciences, Faculty of Medicine, and Norwegian Center for Stem Cell Research, University of Oslo, 0317 Oslo, Norway.|Department of Molecular Medicine, Institute of Basic Medical Sciences, Faculty of Medicine, and Norwegian Center for Stem Cell Research, University of Oslo, 0317 Oslo, Norway.|Department of Molecular Medicine, Institute of Basic Medical Sciences, Faculty of Medicine, and Norwegian Center for Stem Cell Research, University of Oslo, 0317 Oslo, Norway.