Fig. 2. Tau expression causes changes in actin reorganization following PDGF stimulation. 3T3 cells transiently transfected with tau were stimulated with PDGF for 10 minutes or 7 hours, fixed and labeled with phalloidin-Alexa594. Panels A-C show the actin morphology of non-transfected control cells following PDGF treatment as indicated. Panels D-F show the actin morphology in tau-expressing cells similarly treated. Tau-transfected cells were identified by labeling with the polyclonal tau antibody CR (G-I). (J) Quantification of cells showing PDGF-induced actin fiber breakdown in the presence and absence of tau. Percentage of non-transfected cells (open bars) and tau-transfected cells (black bars) showing actin stress fiber breakdown was determined after either 10 minutes or 7 hours PDGF treatment as described in Materials and Methods. (K-L) Expression of a constitutively active form of Src also disorganized the actin cytoskeleton. Labeling for activated Src (phospho-Y416) (K) and phalloidin (L) are shown. Bar in A, 10 µm (applies to panels A, B, D-I). Bar in C, 10 µm.