Fig. 1.

Cortical protein oscillation underlies wave initiation and propagation. a Key model components and their interactions. b Model prediction that a localized GTP-Cdc42 pulse results in nucleation of a cortical patch. In the simulation shown, this external activation was transient, i.e., after 5 s it was turned off for the rest of the simulation. Top: temporal and spatial profiles of the initial Cdc42 activation. Bottom: spatial-temporal evolution of Cdc42 cortical density. c Model prediction that oscillation of cortical protein requires a threshold activation level. d Local cortical protein oscillation during wave propagation. Left: the model prediction of the time curves of F-BAR and actin oscillation at the epicenter, indicated by a cyan box in Fig. 1b, bottom. Right: experimental results show similar oscillations of cortical proteins. e Characteristics of wave propagation. Left: model prediction. Right: experimental measurement. Top: stable phase shift in the cortical oscillation between neighboring areas. The locations are marked by blue squares and green squares in the corresponding cases, in which they are 2.5 μm apart in model result (left bottom) and 2.88 μm apart in experiment (right bottom). The two ROIs are chosen to show that oscillations at the different locations have a stable phase shift, a feature that holds for any two ROIs along the direction of wave propagation. Bottom: snapshots of F-BAR cortical density profiles over time. For the model result, the time is relative to when the transient Cdc42 activation stops in Fig. 1b. In the experiment, the F-BAR level is the FBP17 fluorescence intensity minus background fluorescence, normalized by the maximum fluorescence