1. Physics Department, McGill University, Montreal, QC H3A2T8, Canada
2. Université Lyon, Ecole Normale Supérieure de Lyon, Laboratoire de Physique, UMR 5672, Université Claude Bernard Lyon 1, CNRS, 69342, Lyon, France
3. Program in Biophysics, Harvard University, Cambridge, MA 02138
4. Joseph Henry Laboratory of Physics, Princeton University, Princeton, NJ 08544
5. Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544
6. Department of Stem Cell and Developmental Biology, UMR3738, Institut Pasteur, 75015 Paris, France