Department of Biology, Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland, PhD Program in Systems Biology, University of Zurich and ETH Zurich, Zurich, Switzerland and Faculty of Science, University of Zurich, Zurich, Switzerland Department of Biology, Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland, PhD Program in Systems Biology, University of Zurich and ETH Zurich, Zurich, Switzerland and Faculty of Science, University of Zurich, Zurich, Switzerland.