Fig. 7. Altering PAK4 expression alters EF motility. (A) Morphology of fibroblasts with altered PAK4 levels. Phase-contrast images of 3T3 cells stably transfected with PAK4 (a) or empty vector (b) show that most PAK4 transfectants were flatter and more bipolar than controls, in which 20-25% of cells appear spherical before EF application. Primary fibroblasts from mouse embryos whose PAK4 expression was knocked out by homologous recombination (PAK4^-/-; c) and PAK4-expressing heterozygotes (PAK4^+/-; d) were morphologically indistinguishable. Scale bar, 40 µm. (B) Altered PAK4 expression alters EF-motility speed. EF-motility speed of PAK4 transfectants (2 hours; 6 V cm^-1) was significantly greater than control 3T3 cells (P<0.05, marked with ^*). Embryonic fibroblasts from PAK4-null mice (PAK4^-/-) migrated significantly less rapidly than fibroblasts from PAK4-heterozygous littermates (PAK4^+/-) (P<0.05). At least 17 cells were tested in each of three experiments for each comparison.