1. Department of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, Zurich CH8057, Switzerland.
2. Life Science Zurich Graduate School, ETH and University of Zurich, Zurich 8057, Switzerland.
3. Center for Microscopy and Image Analysis, University of Zurich, Winterthurerstrasse 190, Zurich CH-8057, Switzerland.