1. EMBL Mouse Biology Unit; Monterotondo Rome Italy
2. Department of Biological Science, Florida State University; Tallahassee FL USA
3. Institut Curie, Centre de recherche; Paris France
4. Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche UMR218, Laboratory of Nuclear Dynamics and Genome Plasticity; Paris France
5. EMBL Meyerhof Str.; Heidelberg Germany