Fig. 5. Rac2^D57N expression in serum-starved bone-marrow-derived macrophages inhibits filopodia/retraction fiber formation upon readdition of macrophage medium. (A) The Rac activity is shown of macrophages that were either unstarved (steady state) or starved (basal) for 2 hours in the absence of M-CSF and serum, and then stimulated with macrophage medium. Rac activity was normalized to total Rac expression, and data are expressed as fold stimulation of Rac activity relative to basal (starved) macrophages. (B) Data are expressed as the percentage of total transfected cells with filopodia/retraction fibers. The actin structures of between 50 and 150 transfected cells were examined for each condition. Data represent two independent experiments. (C) Macrophages plated on coverslips were transfected with pIRES2-EGFP expression constructs for empty vector, Rac2^wt or Rac2^D57N and starved for 2 hours in the absence of M-CSF and serum. Cells were either unstimulated or stimulated for 30 minutes in macrophage medium containing 10% serum and 20% L cell medium containing M-CSF. Actin was visualized with rhodamine-phalloidin. Scale bar, 10 µm.