Oscillatory instabilities of intracellular fiber networks

D. discoideum shares many common features of actin dynamics and essential responses with eukaryotic cells and cancer cells. Therefore, most properties of the oscillations are well studied in the simpler biological model system. However, the properties and the underlying mechanisms of the recently found autonomous cytoskeletal oscillations are still unexplored. Questions such as what the roles of this autonomous oscillation in chemotaxis are, and how external stimulation affects autonomous oscillations are intriguing but unanswered. This study starts by investigating actin dynamics of cells in the absence of external stimuli. We analyze thousands of cells to get a stochastically significant mean. In the part on intrinsic oscillations, we report on the properties like the distribution of oscillations, role of actin regulating proteins such as Aip1, coronin and myosin II and propose an underlying mechanism. In the second chapter, we investigated how external stimulation alters the intrinsic frequency. With dose dependence experiments and careful examination of the different sections of the actin polymerization, depolymerization and recovery, we extend our model to account for the chemotatic responses. We also use the experimental data to verify an existing model of actin dynamics and modify it according to our experimental results. Finally, we investigate the role of myosin II in actin dynamics. Although myosin II is not directly involved in actin regulation, it is essential for effective cellular functions such as movement, chemotaxis and cytokinesis