1. National Institute for Basic Biology/Center for Integrative Bioscience, 38 Nishigounaka, Myodaiji-cho; Okazaki 444-8585 Japan
2. Present address: Molecular Membrane Biology Laboratory, RIKEN, 2-1 Hirosawa, Wako; Saitama 351-0198 Japan
3. Institute for Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku; Tokyo 113-0032 Japan
4. Present address: Osborn Memorial Laboratory, Department of Molecular, Cellular and Developmental Biology, Yale University; 165 Prospect Street New Haven CT 6520-8104 USA
5. Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University; Sendai 980-77 Japan
6. Form and Function, PRESTO, Japan Science and Technology Corporation, 4-1-8 Honcho; School of Advanced Sciences, the Graduate University for Advanced Studies, Shonan Villege; Kawaguchi 332-0012 Hayama Kanagawa 240-0193 Japan