engleski

Intracellular Rac1 Dynamics: From Imaging to Models

Dictyostelium amoebae can change their polarity within 20 seconds, and thus undergo the fastest polarization reversal among eukaryotic cells. This repolarization is heralded by the translocation of Rac1 GTPases from the Rho family to the incipient leading edge of the cell. Rac1 GTPases regulate activity of multiple effector proteins involved in the regulation of actin assembly, which is the key determining factor of cell polarity. At the cell front, Rac1 activates the Scar/WAVE complex and thereby stimulates the Arp2/3-mediated actin polymerization. At the cell back, Rac1 regulates stability of the cell cortex by initiating formation of a complex containing IQGAP-related protein DGAP1 and a heterodimer of actin-bundling proteins cortexillins. We present and compare results of experimental and modelling approaches to investigate the dynamics of Rac1 GTPases in Dictyostelium amoebae. The Rac1 activity was monitored over time by confocal microscopy using a specific fluorescent biosensor. Besides active Rac1, fluorescently labelled DGAP1 was also monitored. Cortical dynamics of these proteins was processed by QuimP software, visualized in the form of kymographs, and studied by wavelet-based cross-correlation analysis. We observed that active Rac1 and DGAP1 in the cell cortex exhibit anti-correlated oscillations in the form of standing and travelling waves (Figure 1). In order to gain insight into the molecular mechanisms underlying the observed dynamics, we formulated a reaction- diffusion model that incorporates interactions between Rac1, DGAP1 and a Rac1-inactivating GAP protein. The model was able to reproduce the basic features of obtained experimental results (Figure 2).

Rho GTPases ; Rac1 ; cell motility ; actin cytoskeleton ; Dictyostelium ; IQGAP ; reaction-diffusion model

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