Fig. 1. Involvement of Abl PxxP motifs in regulating filopodium formation during attachment. (A) Expression of Abl and variants in Abl-double-knockout cells detected by western blotting with anti-Abl antibody [K-12, recognizing residues 521-531 in kinase domain (Woodring et al., 2001)], which binds equally to wild-type and mutated forms of Abl used in this study (data not shown). Numbers to the left of blots indicate relative molecular mass in kDa. (B) Serum-starved Abl-double-knockout (DKO) cells stably expressing various forms of Abl were plated on coverslips coated with 10 µg/ml fibronectin and fixed at 20 minutes. The fixed cells were stained for DNA (blue), F-actin (red), and Abl (green) with Hoechst 33342, Texas-Red-labelled phalloidin and Alexa Fluor 488-labeled anti-Abl (8E9), respectively. Scale bar: 10 µm. (C) The number of filopodia was counted on fixed Abl-double-knockout cells. Graph represents mean ± s.e.m. number of filopodia per cell. The number of cells examined is shown above the bars. P<0.05 when compared with Abl-double-knockout cells re-expressing Abl.