1. Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan
2. Department of Physiology, Division of Life Sciences, Faculty of Medicine, Osaka Medical College, Osaka, Japan
3. Division of Biology and Biological Engineering 156-29, California Institute of Technology, Pasadena, California
4. Department of Anatomy, St. Marianna University School of Medicine, Kawasaki, Kanagawa, Japan