Fig. 2.

Membrane shape changes accompany traveling wave propagation. a Model predicts that the local membrane shape correlates with the F-BAR cortical density at the wavefront during wave propagation. The grayish meshes represent the membrane shapes in three-dimensional space (X, Y, Z) with a perspective angle; the inverted density maps are the corresponding F-BAR densities on the membrane, which is projected onto the two-dimensional X–Y plane. The scale bar for the x–y dimension is 5 μm and for the z-dimension is 200 nm. For the purpose of demonstration, the snapshots in Fig. 2a only show a part of the simulated membrane patch. The wave propagates beyond the domain defined in the snapshots until it approaches the boundary of the membrane patch; there, the wave subsides and eventually disappears, as the local membrane is clamped (Supplementary Movie 2 and Supplementary Fig. 2). b A zoom-in view of the local cortical rhythm along the magenta dash line across the cortex marked in Fig. 2a at t = 0, 2, and 4 s. Blue lines: local membrane shape. Magenta lines: F-BAR cortical level. The red arrows mark the locations with the largest membrane curvature. c Model prediction on temporal evolutions of the local F-BAR cortical level, membrane height, and rate of membrane height changes (dh/dt) at the location of the magenta square in Fig. 2a. d Experimental measurement of the spatial-temporal changes in F-BAR cortical level (by TIRFM) and membrane height (by SRIC) during traveling wave propagation. Left: kymographs of the local F-BAR cortical level and the corresponding relative membrane height. Right: time curves representing the local F-BAR cortical level, membrane height, and the rate of membrane height changes (dh/dt) at a fixed location. From SRIC measurements, we estimate the maximum membrane height to be ~140 nm (Supplementary Fig. 3). Note that this number is a very rough estimate, as the refractive indexes both inside and outside of the cell may undergo variation, due to changes in salt concentration and the organelle proximity. We therefore used the normalized membrane height in the experimental plot to avoid systematic error