1. Department of Gastroenterology, General Hospital, Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China
2. Key Laboratory of Fertility Preservation and Maintenance of Ministry of Education, Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China