1. Department of Orthopedic Surgery, Keio University School of Medicine, Tokyo, Japan.
2. Department of Physiology, Keio University School of Medicine, Tokyo, Japan.
3. Electron Microscope Laboratory, Keio University School of Medicine, Tokyo, Japan.
4. Division of Microscopic Anatomy, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan.
5. Division of Genetics and Development, Krembil Research Institute, University Health Network, Toronto, Ontario, Canada.