Fig. 4. Cortactin tyrosine phosphorylation induced by N. meningitidis is required for the formation of actin-rich cell projections promoting bacterial uptake. HBMECs transiently transfected with GFP alone, wild-type GFP-cortactin or a GFP-tagged cortactin mutant deficient in tyrosine phosphorylation (GFP-cortactin_Y/F), as indicated, were infected for 3 hours with the 2C43 wild-type strain of N. meningitidis. (A) Cells were then double stained for actin and ezrin, and analysed by confocal microscopy. (right) Higher magnification of the inset in the middle panels. (B) The frequency of formation of either actin-rich cell projections or bundles of actin filaments at bacterial entry sites in cells expressing high levels of both GFP-cortactin and GFP-cortactin_Y/F was determined by counting 40 cells. Average values (± s.e.m.) are presented from four independent experiments.