1. Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 060, Japan,
2. Division of Morphogenesis, Department of Developmental Biology, National Institute for Basic Biology, Okazaki 444‐8585, Japan,
3. Department of Molecular Biology, Faculty of Science, Nagoya University, Chikusa‐ku, Nagoya 464‐01, Japan,
4. Department of Tumor Cell Biology, The Tokyo Metropolitan Institute of Medical Science, 3‐18‐22 Honkomagome, Bunkyo‐ku, Tokyo 113, Japan,
5. Department of Molecular Biomechanics, The Graduate University for Advanced Studies, Okazaki 444‐8585, Japan,
6. Precursory Research for Embryonic Science and Technology, Japan Science and Technology Corporation, Hikari‐dai, Kyoto 619‐02, Japan