IPLS Invited Speaker - Dr Jose Negrete

Title: Fluctuations and oscillatory instabilities in the actin cytoskeleton of Dictyostelium discoideum

Abstract:  Biological systems with their complex biochemical networks are known to be intrinsically noisy. The actin polymerization of chemotactic amoeboid cells operates close to the onset of oscillations. Dynamical systems typically display a monotonically increasing relation between amplitude and temporal coherence under noisy conditions. Here we investigate the cytoskeletal dynamics of Dictyostelium discoideum and found surprisingly that the amplitude of cytoskeletal oscillations decreases with increasing correlation time. We show that this behavior can be captured by a generic nonlinear oscillator model, that includes an amplitude dependent random dephasing. To test the limits of this phenomenological description, we perturbed experimentally the cytoskeletal dynamics by a short chemoattractant pulse and measured the spatio-temporal response of filamentous actin reporters and depolymerization regulators Coronin1 and Aip1. After pulsing, we observed self oscillating cells to relax back to the prior oscillatory state after a transient. Particularly long transients were observed for cells initially displaying highly correlated oscillations. This gradual recovery process, which can be accounted for by introducing slow components in the model, provides a hint of the variety of time scales in which the motility and chemotactic signaling systems operate.