Research Topic: Cell Motility and Cell Mechanics using novel laser-based optical tools
Our long-term goals are to understand cell motility, which is critical for immunological defense and wound healing, but unwanted during metastatic cancers. Because these processes are ultimately mechanical in nature, our focus is developing and applying new laser-based optical instrumentation with high-resolution microscopy imaging to understand cellular mechanics.
What tools do we use? In addition to mature biochemical and cell biological techniques, we’ve developed and invented a number of advanced laser-based optical techniques to study live-cell processes. One example is analytical. Using laser-scanning confocal microscopy, we’ve developed new quantitative paradigms that push its limits of resolution, allowing the depletion forces of polymerizing actin cytoskeleton to be observed for the first time. A second example is new instrumentation and analysis. Using ultra-high resolution laser-tracking (‘nano-tracking’), we invented a new way (“microrheology”) to measure cell mechanics during physiological processes. For example, the shapes of cells during cell division (cytokinesis) are linearly related to mechanical moduli of cellular cortex across many cytoskeletal mutants. Other instrumentation that we develop are optical tweezers (photonic forces), atomic force microscopy, and total-internal reflectance fluorescence microscopy.
What’s an example of our discoveries? The intracellular bacterial pathogen, Listeria monocytogenes, causes food-born disease. Like other more severe pathogens (Rocky Mountain spotted fever bacteria and smallpox virus), Listeria ‘hijack’ host cell proteins to generate actin rocket tails that push bacteria into adjacent cells, thus spreading infection. These host cell proteins are the same proteins used during cell motility and phagocytosis, hence providing insight into normal cellular function. Using high-resolution ‘nano-tracking’, we discovered that Listeria moves with step-like motions and the steps are the size of the actin monomers used to construct tails. Steps are completely unexpected and shatter prior models of actin-based motility (see http://www.jhu.edu/cmml/ for animations of models).
Girard, K.D., Kuo, S.C., and Robinson, D.N. (2006) Dictyostelium myosin-II mechanochemistry promotes active behavior of the cortex on long time-scales. PNAS 103, 2103-2108.
Girard, K.D., Chaney, C., Delannoy, M., Kuo, S.C., and Robinson, D.N. (2004) Dynacortin contributes to cortical viscoelasticity and helps define the shape changes of cytokinesis. EMBO J 23(7), 1536-46.
McGrath, J.L., Eungdamrong, J., Fisher, C.I., Peng, F., Mahadevan, L., Mitchison, T.J., and Kuo, S.C. (2003) The force-velocity relationship for the actin-based motility of Listeria monocytogenes. Curr Biol 13, 329-332.
Kuo, S.C., and McGrath, J. L. (2000) Steps and fluctuations of Listeria monocytogenes during actin-based motility. Nature 407, 1026-9.
Yamada, S., Wirtz, D., and Kuo, S.C. (2000) Mechanics of living cells measured by laser tracking microrheology (LTM). Biophys. J. 78, 1736-47.