1. Laboratory of Applied Genetics, Department of Animal Resource Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
2. Biomedical Group, Takara Shuzo Co., Ltd., Otsu, Shiga -ken 520-21, Japan
3. Laboratory of Applied Genetics, Department of Animal Resource Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, and Laboratory of Developmental and Reproductive Biotechnology, Department of Animal Resource Sciences, School of Veterinary Medicine and Life Sciences, Azabu University, Fuchinobe, Sagamihara-shi 229-8501, Japan