1. Joint Faculty of Veterinary Medicine, Yamaguchi University, Yoshida 1677-1, Yamaguchi-shi, Yamaguchi 753-8515, Japan
2. Center for Gene Research, Yamaguchi University, Minami Kogushi 1-1-1, Ube-shi, Yamaguchi 755-8505, Japan
3. Institute of Radioisotope Research and Education, Yamaguchi University, Minami Kogushi 1-1-1, Ube-shi, Yamaguchi 755-8505, Japan