Department of Physics
February 24, 2015
Cytoskeletal dynamics in cell division and polarized cell growth
The polarization and division of eukaryotic cells, including model organisms fission and budding yeast, relies on a dynamic network of actin filaments nucleated by formin proteins. During polarized yeast growth, actin filaments nucleated at sites of cell growth bundle to form actin cables that guide the movement of vesicles and organelles toward the cell cortex. During cytokinesis, actin filaments nucleated at medial cortical nodes are captured by myosin-II from neighboring nodes and pulled together into a contractile ring. We used computer simulations to study these dynamics. Individual filaments were modeled as semiflexible polymers in 3D undergoing turnover mediated by cofilin severing. Attractive interactions simulate filament bundling by actin cross-linkers such as fimbrin and alpha-actinin. Forces by motor proteins are simulated as tangential forces along the filaments. By varying the model parameters we find different states of organization depending on formin nucleation geometry, cross-linker activity, filament severing, and motor activity. Actin cables form bundled and unbundled phases with parallel or antiparallel orientations. The cytokinetic network can organize into closed rings, disconnected clump and meshwork phases. These results agree with many prior experimental observations in cell mutants. The also provide a test to evaluate the accuracy of continuum mean-field theories of the cytoskeleton.