Ryuichi Nishihama1, Satoshi Naramoto2,3. 1. Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502, Japan. nishihama@lif.kyoto-u.ac.jp. 2. Graduate School of Life Sciences, Tohoku University, Sendai, 980-8577, Japan. 3. Department of Biological Sciences, Faculty of Science, Hokkaido University, Hokkaido, 060-0810, Japan.