1. Department of Cell Biology; Graduate School of Medicine; Kyoto University; Sakyo-ku Kyoto 606-8501 Japan
2. Laboratory of Biological Science; Graduate School of Frontier Biosciences and Graduate School of Medicine; Osaka University; 1-3 Yamadaoka, Suita Osaka 565-0871 Japan
3. Division of Molecular and Cellular Biology; Graduate School of Medical and Dental Sciences; Niigata University; Chuo-ku Niigata 951-8510 Japan
4. MRC National Institute for Medical Research; London NW7 1AA UK
5. Department of Cell and Developmental Biology; Graduate School of Biostudies; Kyoto University; Sakyo-ku Kyoto 606-8502 Japan