1 Institut Necker-Enfants Malades, INSERM U1151-CNRS UMR8253, Université de Paris, Faculté de Médecine, 75730 Paris Cedex 15, France. Electronic address: claude-agnes.reynaud@inserm.fr.
2 Molecular Biology Section, Division of Biological Sciences, Department of Cellular and Molecular Medicine, TATA Institute for Genetics and Society, University of California, San Diego, La Jolla, CA 92093-0377, United States. Electronic address: shedrick@ucsd.edu.