About the Authors
Department of Developmental Biology, Stanford University School of Medicine, Stanford, California, United States of America
Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, United States of America
The authors have declared that no competing interests exist.
AJM and RN conceived and designed the experiments. AJM performed the experiments. AJM and RN analyzed the data. AJM and RN contributed reagents/materials/analysis tools. AJM and RN wrote the paper.