1. Max Planck Institute for Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
2. Queen Mary University of London, School of Biological and Chemical Sciences, Mile End Road, Fogg Building, E1 4NS London, UK
3. Max Planck Institute for Molecular Biomedicine, Röntgenstraße 20, 48149 Münster, Germany
4. The Hubrecht Institute for Developmental Biology and Stem Cell Research, Uppsalalaan 8, Utrecht, The Netherlands