1. *Department of Reproductive Biology and Pathology, National Institute for Child Health and Development, Tokyo, 157-8535, Japan;
2. Department of Basic Medical Science, Mudanjiang Medical College, Mudanjiang, 157011, China;
3. Department of Obstetrics and Gynecology, Kanazawa University, School of Medicine, Kanazawa, 920-8640, Japan; and
4. Virology Division, National Cancer Center Research Institute, Tokyo, 104-0045, Japan