1. Furusawa MorphoGene Project, Research Development Corporation of Japan, ERATO, Tsukuba, Japan
2. Institute of Molecular Embryology & Genetics, Kumamoto University, School of Medicine, Kuhonji 4‐24‐1, Kumamoto, 862, Japan
3. Graduate School of Science & Technology, Kumamoto University, Kumamoto, Japan
4. Department of Anatomy, Kumamoto University, School of Medicine, Kumamoto, Japan
5. Institute of Development, Ageing and Cancer, Tohoku University, Sendai, Japan
6. Molecular Biology Research Laboratory, Daiichi Pharmaceutical Co., Ltd, Tokyo, Japan