1. Department of Anatomy and Embryology, Faculty of Medicine, University of Tsukuba, 1–1-1 Tennodai, Tsukuba, Ibaraki 305–8575, Japan
2. Laboratory Animal Resource Center (LARC), Faculty of Medicine, University of Tsukuba, 1–1-1 Tennodai, Tsukuba, Ibaraki 305–8575, Japan
3. Ph.D. Program in Human Biology, School of Integrative and Global Majors, University of Tsukuba, 1–1-1 Tennodai, Tsukuba, Ibaraki 305–8575, Japan