1. Department of Organ Anatomy and Nanomedicine, Graduate School of Medicine, Yamaguchi University, 1-1-1 Minami-Kogushi, Ube, Yamaguchi 755-8505, Japan
2. EM Application Group, EM Business Unit, JEOL Ltd., Japan
3. Department of Obstetrics and Gynecology, Graduate School of Medicine, Yamaguchi University, 1-1-1 Minami-Kogushi, Ube, Yamaguchi 755-8505, Japan
4. Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, CA 90095, USA
5. Institute for Integrated Cell-Material Sciences, Institute for Advanced Study, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan