1. Faculty of Life and Environmental Science, University of Yamanashi, Yamanashi 400-8510, Japan
2. Present: Department of Basic Medical Sciences for Radiation Damages, National Institute of Radiological Sciences, Chiba 263–8555, Japan
3. Advanced Biotechnology Center, University of Yamanashi, Yamanashi 400-8510, Japan
4. Laboratory of Animal Reproduction, Graduate School of Veterinary Science, Azabu University, Kanagawa 252-5201, Japan