1. Department of Surgery, Graduate School of Comprehensive Human Sciences; University of Tsukuba; 1-1-1 Tennodai Tsukuba 305-8575 Japan
2. Division of Organ Replacement Research, Center for Molecular Medicine; Jichi Medical School; Tochigi 329-0498 Japan
3. Division of Animal Science; National Institute of Agrobiological Sciences; Ikenodai Tsukuba 305-0901 Japan