Institute for Medical Engineering & Science, The Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts, United States of America.|Laboratory of genetic instability and nuclear organization, CEA, Fontenay-aux-Roses, France.|Laboratory of genetic instability and nuclear organization, CEA, Fontenay-aux-Roses, France.|IBENS, Ecole Normale Supérieure, Paris, France and Mathematical Institute, University of Oxford, Oxford, United Kingdom.