Fig. 6. The activation of Rac1 GTPase is required for cortactin recruitment and the formation of actin-rich cell projections promoting bacterial uptake. (A) The upper row (a) shows a cell expressing the GFP-Rac1-DN and the lower row (b) shows a nontransfected control cell. Both were infected with the bacterial wild-type strain. HBMECs transiently transfected with the dominant-negative form of Rac1 coupled to GFP (GFP-Rac1DN) were infected for 3 hours with the 2C43 wild-type strain of N. meningitidis. Cells were then double stained for actin (red) and cortactin (blue), and were analysed by confocal microscopy. (right) Merged images (overlay) of the same fields. (B) The frequency of formation of either actin-rich cell projections or bundle of actin filaments at bacterial entry sites in both control and Rac1-DN-expressing cells was determined by counting 40 cells. Average values (± s.e.m.) are presented from three independent experiments.