Amoeboid Shape Dynamics on Flat and Topographically Modified Surfaces

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I present an analysis of the shape dynamics of the amoeba Dictyostelium discoideum, a model system for the study of cellular migration. To better understand cellular migration in complicated 3-D environments, cell migration was studied on simple 3-D surfaces, such as cliffs and ridges. D. discoideum interact with surfaces without forming mature focal adhesion complexes. The cellular response to the surface topography was characterized by measuring and looking for patterns in cell shape. Dynamic cell shape is a measure of the interaction between the internal biochemical state of a cell and its external environment.

For D. discoideum migrating on flat surfaces, waves of high boundary curvature were observed to travel from the cell front to the cell back.  Curvature waves are also easily seen in cells that do not adhere to a surface, such as cells that are electrostatically repelled from the coverslip or cells that are extended over the edge of micro-fabricated cliffs.  At the leading edge of adhered cells, these curvature waves are associated with protrusive activity, suggesting that protrusive motion can be thought of as a wave-like process.  The wave-like character of protrusions provides a plausible mechanism for the ability of cells to swim in viscous fluids and to navigate complex 3-D topography.

Patterning of focal adhesion complexes has previously been implicated in contact guidance (polarization or migration parallel to linear topographical structures).  However, significant contact guidance is observed in D. discoideum, which lack focal adhesion complexes.  Analyzing the migration of cells on nanogratings of ridges spaced various distances apart, ridges spaced about 1.5 micrometers apart were found to guide cells best.  Contact guidance was modeled as an interaction between wave-like processes internal to the cell and the periodicity of the nanograting.  The observed wavelength and speed of the oscillations that best couple to the surface are consistent with those of protrusive dynamics.  Dynamic sensing via actin or protrusive dynamics might then play a role in contact guidance.