1. Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
2. Howard Hughes Medical Institute, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
3. Department of Developmental Biology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.