About the Authors
Department of Molecular Embryology, Max-Planck Institute of Immunobiology and Epigenetics, Freiburg, Germany
The authors have declared that no competing interests exist.
Conceived and designed the experiments: IB MPS. Performed the experiments: IB. Analyzed the data: IB EL MPS. Contributed reagents/materials/analysis tools: EL BK. Wrote the paper: IB MPS.