1. Centre for Molecular Biology and Neuroscience, Institute of Medical Microbiology, Oslo University Hospital, Rikshospitalet and University of Oslo, Oslo, Norway
2. Gurdon Institute and Department of Pathology, University of Cambridge, Cambridge, United Kingdom
3. Department of Molecular Biology, Massachusetts General Hospital, Howard Hughes Medical Institute, Boston, Massachusetts, USA
4. Department of Genetics, Harvard Medical School, Boston, Massachusetts, USA