1. Laboratory of Molecular Morphology, Department of Animal Science, Graduate School of Agricultural Science, Kobe University, Kobe, Hyogo 657–8501, Japan
2. Laboratory of Histophysiology, Department of Animal Science, Graduate School of Agricultural Science, Kobe University, Kobe, Hyogo 657–8501, Japan
3. Frontier Research Laboratory, Corporate Research and Development Center, Toshiba Corporation, Saiwai, Kawasaki, Kanagawa 212–8582, Japan