1. Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, 565-0871, Japan.
2. CREST, Japan Science and Technology Agency (JST), Osaka University, Suita, Osaka, 565-0871, Japan.
3. Department of Biology, University of Washington, Seattle, WA 98195-1800, USA.
4. Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Osaka 567-0047, Japan.