1. State Key Laboratory of Animal Biotech Breeding, College of Biological Sciences, China Agricultural University , Beijing 100193 , China
2. Reproductive Medical Center, Department of Obstetrics and Gynecology, the Seventh Medical Center of PLA General Hospital , Beijing 100007 , China
3. State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences , Beijing 100101 , China
4. Department of Pathology, the Seventh Medical Center of PLA General Hospital , Beijing 100007 , China
5. College of Veterinary Medicine, Yangzhou University , Yangzhou, Jiangsu 225009 , China