Fig. 6. Podosome formation is initiated at discrete sites at the insertion point of actin fibers into focal adhesions. (A) The overview shows a DsRed SM22 and GFP-zyxin co-transfected cell before (0') and after PDBu treatment (40'). Note the formation of SM22-rich early podosomes in the transition zone between stress fibers and focal adhesions (arrows in enlargement, 2 minutes), and later reassembling podosomes proximal to stress fibers, which are separated from adhesions (enlargement, 38 minutes). (B) Similar data set as in A for a DsRed SM22 and GFP--actinin co-transfected cell. Podosomes formation (inset, 11 minutes) and re-assembly (enlargement, 25 minutes) is initiated within the -actinin-enriched region (arrows). (C) Enlarged view of the rectangular boxed area in B. Note the functional uncoupling of stress fibers (SF) and focal adhesion (FA) and the parallel decrease of adhesion sites (arrows). (D) Selected examples of podosome formation and subsequent adhesion disassembly in DsRed zyxin and GFP--actinin co-transfected cells (ellipses). Note that -actinin is incorporated at early stages of podosomes formation and stays associated with the structures until the complete disassembly of focal adhesion.