Fig. 4. Paxillin is enriched in adhesions of fibroblasts migrating on either 2D or 3D fibronectin matrices. Mouse embryonic fibroblasts (MEFs) were allowed to migrate for 16 hours in the presence of serum on (A) a 2D fibronectin-coated surface or (B) a 3D cell-derived fibronectin-rich matrix (CDM) that is more representative of the in vivo environment. Cells were fixed and stained for F-actin (red), paxillin (green) and fibronectin (blue). Although paxillin-rich adhesions are observed in both conditions, MEFs migrating on the 2D fibronectin are well-spread and exhibit robust actin stress fibers, whereas cells migrating within the 3D CDM display long, thin protrusions (arrows) and limited actin organization. Scale bar: 20 µm.