Fig. 1. MEKK1-deficient fibroblasts show increased adherence characteristic of a defect in rear-end detachment. (A) Wild-type or MEKK1–/– MEFs were serum starved for 8 h, then treated with media with or without 10% fetal bovine serum (FBS). The plates were then inverted and centrifuged at 2300 g for 5 min. Adherent cells remaining attached to the well surface were stained with Wright’s stain and quantitated. Cell adherence is represented as the percent of the total serum-treated cells compared with the non-treated cells; 100% was taken as the number of wild-type cells in the dish before serum challenge, inversion and centrifugation. MEKK1–/– cells with serum challenge is >100% because more cells are retained after centrifugation than for the non-serum-stimulated wild-type cells, indicative of the increased adherence of MEKK1–/– cells. Results shown are the mean ± SEM of at least three independent experiments, and the statistical significance was determined by Student’s t-test. (B) Fibroblasts were resuspended in complete media and allowed to attach to either untreated or fibronectin-coated tissue culture plates. Cells were monitored for 2 h and the number of attached cells determined by phase microscopy. A digital movie of migrating MEKK1+/+ and MEKK1–/– fibroblasts is available as Supplementary data.