About the Authors
Division of Developmental Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom
Vertebrate Development and Genetics, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
The authors have declared that no competing interests exist.
TG, AA, SC, MDC, DLS, and LBZ conceived and designed the experiments, performed the experiments, analyzed the data, and wrote the paper.