1. Division of Biological Science Nara Institute of Science and Technology Ikoma 630‐0192 Japan
2. RIKEN BioResource Research Center Tsukuba 305‐0074 Japan
3. Precursory Research for Embryonic Science and Technology Japan Science and Technology Agency Kawaguchi‐shi 332‐0012 Japan
4. Department of Biological Chemistry, College of Bioscience and Biotechnology Chubu University Kasugai 487‐8501 Japan
5. RIKEN Center for Sustainable Resource Science Yokohama 230‐0045 Japan
6. Graduate School of Science The University of Tokyo Tokyo 113‐0033 Japan