Fig. 7.

Actin and Arp2/3 dynamics in chemotaxis. The cells shown respond to cAMP applied through a micropipet that is placed outside the frames shown. The direction of the diffusion gradients is indicated by arrows. (A) A cell labeled with full-length LimE-GFP recorded at a frame rate of 100 msec. (B and C) Cells labeled with GFP-Arp3 (green) and mRFP-LimEΔcoil (red). Yellow regions indicate merge of the two labels. The pattern of dense actin assemblies in B resembles the pattern in A, showing that these structures are enriched in the Arp2/3 complex. At subsequent stages, Arp2/3-rich actin structures are distributed along the region of the cell border that is exposed to higher cyclic-AMP concentrations. (C) Arp2/3-rich actin structures are preferentially accumulated at the base of filopods that point toward the source of the gradient. (In B and C, network structures are not visible, because the resolution of dual-emission fluorescence recordings is limited.) Time is indicated in seconds. (Scale bar: 5 μm.)