1. Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
2. Cancer Biology Program, Stanford University School of Medicine, Stanford, CA 94305, USA.
3. Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
4. Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
5. Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA.