We previously demonstrated that mRNAs for the subunits of the Arp2/3 complex localize to protrusions in fibroblasts (Mingle et al. in J Cell Sci 118:2425-2433, 2005). However, the signaling pathway that regulates Arp2/3 complex mRNA localization remains unknown. In this study we have identified lysophosphatidic acid (LPA) as a potent inducer of Arp2 mRNA localization to protrusions in fibroblasts via the RhoA-ROCK pathway. As RhoA is known to be activated locally in the cells, we sought to understand how spatial activation of Rho affects Arp2 mRNA localization. By sequentially performing fluorescence resonance energy transfer (FRET) and fluorescence in situ hybridization (FISH), we have visualized active RhoA and Arp2 mRNA in the same cells. Upon LPA stimulation, approximately two times more cells than those in the serum-free medium showed mutually exclusive localization of active RhoA and Arp2 mRNA. These results demonstrate the importance of localized activation of Rho in Arp2 mRNA localization and provide new insights as to how Rho regulates Arp2/3 complex mRNA localization. To our best knowledge, this is the first report in which FRET and FISH are combined to detect localized protein activity and mRNA in the same cells. This method should be easily adopted for the detection of other fluorescence protein based biosensors and DNA/RNA in the same cells.