1. Department of Biomedical Sciences, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA, USA.
2. Department of Biology, University of Pennsylvania, 433 South University Avenue, Philadelphia, PA, USA.
3. Whitehead Institute, Cambridge, MA, USA.
4. Department of Pathobiology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA, USA.
5. Center for Vertebrate Genomics, Cornell University, Ithaca, NY, USA.
6. Department of Tissue and Embryology, Hubei Provincial Key Laboratory of Developmentally Originated Disease, School of Basic Medical Sciences, Wuhan University, Wuhan, Hubei Province, China.