Fig. 4. (A) Overexpression of palladin isoforms in COS-7 cells results in striking, but distinct, actin organization phenotypes. Low-magnification images of COS-7 cells stained for F-actin and exogenous palladin 24 hours after transfection of the 90 kDa or 140 kDa isoforms. The overexpression of the 90 kDa isoform results in the formation of unusually robust actin-cables, whereas overexpression of the 140 kDa isoform results in the assembly of compacted star-like F-actin arrays. In the merged images, phalloidin staining is shown in green and myc-epitope staining is in red. Bars, 50 µm. (B) High-magnification images of single cells from the same fields. Bars, 50 µm. (C) Bar graph, indicating the differences between phenotypes overexpressing the 90 kDa and 140 kDa isoforms. For each transfection, 100 cells were scored blindly and F-actin phenotypes were grouped into one of three classes: stars-like assemblies, large bundles and small bundles (examples are given in supplementary material, Fig. S3). Overexpression of the 140 kDa isoform leads to more pronounced, compacted F-actin phenotype than overexpression of the 90 kDa isoform.