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Anders Carlsson has been at Washington University since 1983, and is Professor of Physics. His research interests are focused on modeling the polymerization processes underlying the crawling motions of cells. This work is being performed in collaboration with Professor John Cooper at the Washington University School of Medicine. The motions of cells, extensions of their boundaries, and cell division often involve polymerization and depolymerization of the protein actin. This protein forms long, fairly stiff filaments, whose growth can supply the mechanical force necessary for cell motion or shape changes. The filaments are often found in branched or cross-linked networks. The distribution of actin inside cells displays spontaneous dynamic behaviors that are similar to those of an excitable medium. The modeling work treats these phenomena with methods including Brownian-dynamics and stochastic-growth simulations, and analytic theory. The main goals of the modeling are to are to pin down the key mechanisms driving actin waves and polarization of migrating cells, to establish how actin polymerization can "sculpt" the cell membrane in processes such as endocytosis, and to clarify force generation by actomyosin and actin bundles.

Shown above is the structure of an actin wave propagating across a 3 by 3 micron piece of cell membrane. Such waves occur in Dictyostelium and several other cell types, and we are working on pinning down the networks that drive them. Take a look at the movie of simulated fluorescence . These results were obtained from a stochastic model of actin filament growth combined with Brownian dynamics simulations. More recently, under support from NIH Grant R01 GM107667, we have extended these methods to treat endocytosis.