The actin cytoskeleton is the major cell surface components and plays pivotal roles in cancer invasion, immune cell migration and neural network formation. Dynamic biological systems such as actin-based motility function in a complex manner even in a single cell. Because of this complexity, it is sometimes difficult to know real molecular activities by observing the phenotypes from the outside of the cell. To overcome such deficiencies, we proved that individual fluorescently-labeled proteins can be visualized in living cells, and using this technique, we have elucidated the dynamic interactions between cell signaling and actin remodeling activities. For example, the formin homology protein mDia1 was shown to have the astounding property of adding more than seven hundred actin subunits per second to the growing F-actin end and move processively over long distance (Figure 1). In the cell steering machinery lamellipodia, our data show that actin undergoes rapid polymerization and disassembly cycles by a mechanism distinct from the commonly accepted ‘treadmilling’ theory. We also apply the single-molecule approach to elucidating the mechanisms of action of target-based drugs (Figure 2).

This single-molecule approach, which just emerged in this century, has a wide potential role in elucidating molecular functions in vivo. Our laboratory aims at bringing up researchers capable of expanding the potential of direct molecular behavior observation through research activities.

Figure 1

Figure 1 Rotational movement of an actin filament processively assembling at the mDia1-bound barbed end in vitro (Science 2011).

Figure 2

Figure 2 A rapid increase in the slowly diffusing, cell edge associating protooncogene c-Abl after perfusion of STI571 (imatinib), the first successful target based drug which cures chronic myelogenous leukemia (Mol. Pharmacol. 2009).

Professor: Naoki Watanabe      E-mail:

  • Elucidation of processive actin polymerization mechanisms by formin homology proteins
  • The molecular mechanism regulating actin assembly and disassembly and its physical and biochemical regulations
  • Cell-based high resolution imaging and elucidation of mechanisms of actin of small compounds

Assistant Professor: Tai Kiuchi      E-mail:

  • Elucidation of actin cytoskeleton remodeling mechanisms during cell migration
  • Development of microscopic imaging of spatiotemporal changes in molecular concentration and cell morphology in a living cell by using fluorescent protein, Dronpa.

Selected publications

  • Kiuchi, T., Nagai, T., Ohashi, K. and Mizuno, K. Measurements of spatiotemporal changes in G-actin concentration reveal its effect on stimulus-induced actin assembly and lamellipodium extension. J. Cell Biol. 193: 365-380 (2011)
  • Mizuno, H., Higashida, C., Yuan, Y., Ishizaki, T., Narumiya, S. and Watanabe, N. Rotational Movement of the Formin mDia1 Along the Double Helical Strand of an Actin Filament. Science 331, 80-83 (2011)
  • Watanabe N. Inside view of cell locomotion through single-molecule: fast F-/G-actin cycle and G-actin regulation of polymer restoration. (review) Proc. Jpn. Acad. B. Phys. Biol. Sci. 86: 62-83. (2010)
  • Miyoshi T. et al. Actin turnover-dependent fast dissociation of capping protein in the dendritic nucleation actin network: evidence of frequent filament severing. J. Cell Biol. 175: 947-955 (2006)
  • Higashida C. Miyoshi T., Fujita A., Oceguera-Yanez F., Monypenny J., Andou Y., Narumiya S. and Watanabe N. Actin polymerization-driven molecular movement of mDia1 in living cells. Science 303: 2007-2010 (2004)
  • Watanabe N. and Mitchison T.J. Single-molecule speckle analysis of actin filament turnover in lamellipodia. Science 295: 1083-1086 (2002)
  • Watanabe N. et al. Cooperation between mDia1 and ROCK in Rho-induced actin reorganization. Nat. Cell Biol. 1(3): 136-143 (1999)
Tohoku University> Graduate School of Life Sciences> Department of Biomolecular Sciences