Cell Motion

The lamellipodium at the leading edge of motile cells is a dynamic structure consisting of a dense network of branched actin filaments. These actin filaments polymerize in a region close to the leading edge and undergo retrograde flow towards the main body of the cell. A large number of experimental techniques have been used to monitor the structural aspects of actin networks at the leading edge. However, the role of concentration gradients and local heterogeneity of soluble actin, actin oligomers, and actin regulators in the crowded filament network is little explored.

In collaboration with the lab of Naoki Watanabe (Kyoto University), we use modeling, image analysis, and single molecule fluorescence microscopy to quantify the role of diffuse actin species and their gradients in actin reorganization at the leading edge of motile cells. We further model how these mechanisms contribute to dynamical patterns of protrusion and retraction at the leading edge.

To aid our quantification of actin patterns at the leading edge, we developed Speckle TrackerJ, a particle tracking software for ImageJ to mark the appearance and disappearance of bright spots that correspond to proteins becoming associated to, or dissociated from, the actin network.  We also developed a set of ImageJ plugins (LEAP) to measure leading edge position and intensity.

References
  1. G. L. Ryan, D. Holz, S. Yamashiro, D. Taniguchi, N. Watanabe, D. Vavylonis, "Cell protrusion and retraction driven by fluctuations in actin polymerization: A two-dimensional model," CYTOSKELETON 74:490-503 (2017).
  2. L. M. McMillen and D. Vavylonis, "Model of turnover kinetics in the lamellipodium: implications of slow- and fast- diffusing capping protein and Arp2/3 complex," PHYSICAL BIOLOGY 13:066009 (2016).
  3. E. Vitriol, L. M. McMillen, M. Kapustina, S. Gomez, D. Vavylonis, and J. Q. Zheng, "Two Functionally Distinct Sources of Actin Monomers Supply the Leading Edge of Lamellipodia," CELL REPORTS  11:433-445 (2015).
  4. W. Nie, M.-T. Wei, D. H. Ou Yang, S. S. Jedlicka, D. Vavylonis, "Formation of contractile networks and fibers in the medial cell cortex through myosin-II turnover, contraction, and stress-stabilization," CYTOSKELETON 72:29-46 (2015).
  5. S. Yamashiro, H. Mizuno, M. B. Smith, G. L. Ryan, T. Kiuchi, D. Vavylonis, N. Watanabe, "New single-molecule speckle microscopy reveals modification of the retrograde actin flow by focal adhesions at nanometer scales," MOL. BIOL. CELL 25:1010-1024 (2014).
  6. M. B. Smith, T. Kiuchi, N. Watanabe and D. Vavylonis, "Distributed Actin Turnover in the Lamellipodium and FRAP Kinetics," BIOPHYS. J. 104:247-257 (2013).  
  7. G. L. Ryan, N. Watanabe and D. Vavylonis, "Image Analysis Tools to Quantify Cell Shape and Protein Dynamics near the Leading Edge" (Cell Structure and Function, 2013)  
  8. G. L. Ryan, N. Watanabe and D. Vavylonis, "A review of models of fluctuating protrusion and retraction patterns at the leading edge of motile cells," CYTOSKELETON 69:195-206 (2012).   
  9. G. L. Ryan, H. Petroccia, N. Watanabe and D. Vavylonis, "Excitable actin dynamics in lamellipodial protrusion and retraction," BIOPHYS J., 102:1493-1502 (2012).  
  10. M. B. Smith, E. Karatekin, A. Gohlke, H. Mizuno, N. Watanabe and D. Vavylonis, "Interactive, computer-assisted tracking of speckle trajectories in fluorescence microscopy: application to actin polymerization and membrane fusion," BIOPHYS J., 101:1794-1804 (2011). (Evaluated in Faculty of 1000)