1. Laboratory of Frontier Science, Tokyo Metropolitan Institute of Medical Science, Setagaya-ku, Tokyo 156-8506, Japan
2. Department of Neurology and Research Institute for Diseases of Old Age, Juntendo University School of Medicine, Bunkyo-ku, Tokyo 113-8421, Japan
3. Center for Neurologic Diseases, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115
4. Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan