1. CNRS Unité de Recherche Associée 2578, Department of Developmental Biology
2. Unité du Développement des Lymphocytes, Unité 668, INSERM, Pasteur Institute, 75724 Paris Cedex 15, France.
3. Department of Paediatrics, Imperial College London, The Dubowitz Neuromuscular Centre, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK.
4. Muscle Cell Biology Group, Medical Research Council Clinical Sciences Centre, Imperial College, Du Cane Road, London W12 ONN, UK.