KENBIKYO Vol.53▶No.3 2018
■Feature Articles: Electron Tomography for the Case of TEM, from Soft to Hard

Cell Motility Elucidated by Three-Dimensional Electron Cryo-Microscopy

Takuo Yasunaga, Shinji Aramaki and Tomoya Higo

Abstract: The cryo-electron microscopy is one of the most powerful techniques to elucidate biological molecular structure under nearly physiological conditions. Furthermore, we can also visualise in situ molecular behaviours in cells and tissues at nano-meter resolutions by electron tomography. We here clarified the architecture of filopodia, which is an essential device for cell motility and sensing. We observed the hexagonal actin bundles and their sets, where the actin numbers in the bundles are consistent with those estimated by mechanical balance. The cross-linked structures between actin filaments were averaged and compared with the atomic model resolved by X-ray crystallography; we showed a binding manner of fascin to actin filaments. Besides, we browsed in reconstructed filopodia and so found cooperative bindings of fascin and short actins in the periphery of the actin bundles. Thus we proposed a novel filopodia formation mechanism. We challenged the elucidation of the elongation mechanism by observing the tips of filopodia. Hereafter, cryo-electron tomography will useful for materials in water as well as biological samples.

Key words: Electron cryo-microscopy, electron tomography, single particle analysis, cell motility, filopodia