1. Departments of Orthopediatric Surgery and Molecular Embryology, School of Medicine, Chiba University, 1-8-1 Inohana, chuoku, Chiba 260, Japan
2. Department of Molecular Embryology, School of Medicine, Chiba University, 1-8-1 Inohana, chuoku, Chiba 260, Japan
3. Department of Orthopediatric Surgery, School of Medicine, Chiba University, 1-8-1 Inohana, chuoku, Chiba 260, Japan
4. Centro de Investigaciones Biologicas, Department of Developmental and Cell Biology, Velazquez 144, 28006 Madrid, Spain