1. European Molecular Biology Laboratory (EMBL), Mouse Biology Unit, Campus A. Buzzati-Traverso, Monterotondo-Scalo, 00016 Rome, Italy
2. European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Meyerhofstraße 1, 69117 Heidelberg, Germany
3. Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis, Musculoskeletal and Skin Diseases, National Institute of Health, Bethesda, MD 20892-1592, USA