1. Laboratoire de Biologie Cellulaire, Universite Catholique de Louvain, Place Croix du Sud 5, 1348 Louvain‐la‐Neuve, Belgiumand and UK
2. Department of Obstetrics and Gynaecology, University College London Medical School, 86‐96 Chenies Mews, London WC1E 6HX, UK