Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, 4058 Basel, Switzerland, Swiss Institute of Bioinformatics, 4058 Basel, Switzerland and Novartis Institute for Biomedical Research, CH-4057 Basel, Switzerland Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, 4058 Basel, Switzerland, Swiss Institute of Bioinformatics, 4058 Basel, Switzerland and Novartis Institute for Biomedical Research, CH-4057 Basel, Switzerland.