1. Friedrich Miescher Institute for Biomedical Research, CH-4058 Basel, Switzerland.
2. Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
3. Gruss-Lipper Biophotonics Center, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
4. Transcription Imaging Consortium, Howard Hughes Medical Institute Janelia Farm Research Campus, Ashburn, VA 20147, USA.
5. University of Basel, CH-4003 Basel, Switzerland.
6. Developmental Biology Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.