1. Laboratory for CAG Repeat Diseases, RIKEN Brain Science Institute, Saitama 351-0198, Japan, Laboratory for Structural Biology, RIKEN Harima Institute, Hyogo 679-5148, Japan, Laboratory for Neural Architecture, RIKEN Brain Science Institute, Saitama 351-0198, Japan, and Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan