1. College of Veterinary Medicine, Shaanxi Centre of Stem Cells Engineering and Technology, Northwest A and F University, Yangling, Shaanxi Province, China
2. Department of Pathology, Yangling Demonstration Zone Hospital, Yangling, Shaanxi Province, China
3. Division of Developmental Biology, The Roslin Institute Reader, Royal (Dick) School of Veterinary Studies University of Edinburgh, Easter Bush, Midlothian, EH25 9RG Scotland, UK