Taito Matsuda1, Kinichi Nakashima2. 1. Department of Stem Cell Biology and Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan. Electronic address: tmatsuda@scb.med.kyushu-u.ac.jp. 2. Department of Stem Cell Biology and Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan. Electronic address: kin1@scb.med.kyushu-u.ac.jp.