1. Department of Cell Differentiation, Institute of Molecular Embryology and Genetics (IMEG), Kumamoto University School of Medicine, Kumamoto 860-0811, Japan
2. Department of Cell Differentiation, The Sakaguchi Laboratory of Developmental Biology, School of Medicine, Keio University, Tokyo 160-8582, Japan
3. Center for Tukuba Advanced Research Alliance and Institute of Basic Medical Sciences, University of Tukuba, Tsukuba 305-8577, Japan