1. Department of Developmental Genetics, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, 4‐24‐1 Kuhonji, Kumamoto 862, Japan,
2. Department of Orthopaedic Surgery, Miyazaki Medical College, 6500 Kihara, Kiyotake, Miyazaki 889‐16, Japan
3. Gene Technology Center, Kumamoto University, 2‐2‐1 Honjo, Kumamoto 860, Japan,
4. Department of Morphogenesis, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, 2‐2‐1 Honjo, Kumamoto 860, Japan, and,