1. Department of Anatomy; Division of Anatomy & Embryology; Jichi Medical University; Tochigi 329-0498 Japan
2. Department of Animal Science; School of Agriculture; Tokai University; Minamiaso Kumamoto 869-1404 Japan
3. Laboratory of Animal Science and Medicine; Department of Animal Medical Sciences; Faculty of Science; Kyoto Sangyo University; Kyoto 603-8555 Japan
4. Shizuoka Swine & Poultry Research Center; Shizuoka Prefectural Research Institute of Animal Industry; Shizuoka 439-0037 Japan
5. Division of Development of Advanced Treatment; Center for Development of Advanced Medical Technology; Jichi Medical University; Tochigi 329-0498 Japan