Fig. 4. Arp2/3 engagement precedes translocation of SM22 to early sites of podosome formation. (A) DsRed SM22 and GFP-p20 co-transfected cells before (A) and after 40 minutes of 1 µM PDBu treatment (A'). Note the presence p20-rich dots in both panels. (B) Selected region of the PDBu-treated cell in A' showing p20 and SM22; merged image is shown in the left panel. SM22 is not concentrated in small p20 foci (large arrows), but co-localizes in larger, p20-positive patches proximal to stress fibers (small arrows). (C) Dynamics of GFP-p20 and DsRed-SM22 during a podosome life cycle. Time of PDBu treatment is indicated in minutes and seconds. Note that p20 is concentrated in the spot before, during and after SM22 accumulation.