1. Department of Neuroscience, Pharmacology and Physiology; University College London; London WC1E 6BT United Kingdom
2. Department of Cell and Developmental Biology, Wolfson Institute for Biomedical Research; University College London; London WC1E 6BT United Kingdom
3. Wellcome Trust-MRC Cambridge Stem Cell Institute; Cambridge CB2 1QR United Kingdom
4. Department of Oral Biology, Brain and Muscle Energy Group; University of Oslo; Blindern Oslo N-0317 Norway
5. Department of Anatomy; University of Oslo; Blindern Oslo N-0317 Norway