1. Department of Obstetrics and Gynecology, The First Affiliated Hospital, Sun Yat-Sen University, Guangzhou, Guangdong 510080, P.R. China
2. Department of Pathology, The First Affiliated Hospital, Sun Yat-Sen University, Guangzhou, Guangdong 510080, P.R. China
3. Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA
4. Department of Physiology and Biophysics, University of California, Irvine, CA 92697, USA