1. Laboratory of Animal Reproduction, Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan.
2. Division of Organ Replacement Research, Center for Molecular Medicine, Jichi Medical School, Tochigi 329-0498, Japan.
3. Department of Molecular Life Science, Division of Basic Molecular Science and Molecular Medicine, Tokai University, Kanagawa 259-1193, Japan.