1. EMI-U 9922 Institut National de la Santé et de la Recherche Medicale (INSERM)/Université Paris 7, IFR02, AP-HP, CHU Bichat, 75018 Paris, France
2. Department of Cell Biology, University of Geneva, 1211 Geneva 4, Switzerland
3. Serono Pharmaceutical Research Institute, Serono International SA, CH-1228 Plan-les-Ouates, Geneva, Switzerland