1. Department of Cell Biology, University of Geneva, 1211 Geneva, Switzerland
2. Division of Cell Biology, Institute of Ophthalmology, University College London, EC1V 9EL London, UK
3. Department of Physiology, Center for Research and Advanced Studies, Mexico, D.F., 07360 Mexico
4. Division of Cell Sciences, School of Biological Sciences, University of Southampton, SO16 7PX Southampton, UK
5. Curie Institute, Research Section, Paris 7505, France