12/09/2020

At the cortex of Dictyostelium, the actin cytoskeleton localizes in discrete patches which have been shown to oscillate at different phases. Recent findings suggest that the spatial coordination of actin oscillators is regulated by the G protein subunit G$\beta$, which diffuses rapidly throughout the cell. Upon G$\beta$ sequestration, the following phenomena are observed: (1) higher fraction of actin patches becomes oscillatory; (2) phase difference between different sectors becomes smaller. To understand these observations, we model each actin patch as a conditional oscillator, which is governed by an excitable activator-inhibitor model coupled by bulk diffusion of G$\beta$. Assuming that G$\beta$ promotes the actin activator Arp2/3 in each actin patch, we find that actin oscillations can emerge when the G$\beta$ concentration is low. We show that spatial heterogeneity of G$\beta$ can lead to phase differences in actin oscillators. We consider how additional spatial coupling by Arp2/3 can influence spatial patterning in this system.