1. Friedrich Miescher Institute for Biomedical Research, Novartis Research Foundation, P.O. Box 2543, Maulbeerstrasse 66, 4058 Basel, Switzerland
2. INSERM U309, Institut Albert Bonniot, Faculté de Médecine, Domaine de la Merci, 38706 La Tronche Cedex, France
3. Novartis Institutes for Biomedical Research, Klybeckstrasse, Basel, Switzerland
4. Howard Hughes Medical Institute, The Children's Hospital, The CBR Institute for Biomedical Research, Harvard Medical School, Boston, Massachusetts 02115