1. Institute of Epigenetics and Stem Cells, Helmholtz Zentrum München 1 , D-81377 Munich , Germany
2. Institute of Functional Epigenetics, Helmholtz Zentrum München 2 , D-85764 Neuherberg , Germany
3. Institute of Computational Biology, Helmholtz Zentrum München 3 , D-85764 Neuherberg , Germany
4. Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC) 4 , 1030 Wien , Austria