FMNL2-driven actin assembly rapidly induces de novo cell–cell adhesion formation in response to Rac1 activation. (A) Photoactivation of mCherry-PA-Rac1 in MCF10A cells coexpressing FMNL2-GFP. Rac-1 activity was uncaged through the irradiation, with 488-nm laser light simultaneously exciting FMNL2-GFP. (B) MCF10A cells expressing FMNL2-GFP and mCherry-PA-Rac1 were exposed to blue light for 16 min prior to labeling of E-Cadherin. (C) Time-lapse imaging of MCF10A cells expressing mCherry-PA-Rac1 and LifeAct-GFP transfected with the indicated siRNAs. Compared with control cells, FMNL2 suppression resulted in impaired contact formation (arrows). Insets show mCherry-PA-Rac1 expression (bar, 2 µm). (D) Quantification of C. (E) Quantification of junctional F-actin ratios obtained by line scan profiles from induced GFP- or GFP-Rac1-L61–expressing MCF10A transfected with the indicated siRNAs as in Fig. 4 B. (F) Cartoon illustrating the function of FMNL2. In the presence of active Rac1, FMNL2 becomes localized to the cell–cell contact area, where it associates with the adhesion complex to participate in junctional actin assembly. Error bars indicate SEM. *, P ≤ 0.05.