Syk played a role in migration by stabilizing the leading edge. (A) Time-lapse microscopy of dHL-60 cells transiently transfected with EGFP-Syk, EGFP-Syk K402R, or EGFP-Syk Y348F constructs. Migration on immobilized fibrinogen in response to a gradient of 10 nM fMLP is shown. Images 1 through 8 were recorded at intervals of 30 seconds. EGFP-Syk was enriched at the leading edge of the migrating cell during the observed time period (arrow). In contrast, EGFP-Syk K402R or EGFP-Syk Y348F showed a homogenous distribution within the cell. Both mutants showed multiple unstable lamellipodia and impaired migration (arrowheads). Scale bar equals 10 μm. The series shown are representative for 3 independent experiments. Supplementary video sequences show migrating EGFP-Syk wild-type (Video S1), EGFP-Syk Y348F (Video S2), and EGFP-Syk K402R transfectants (Video S3). (B) Quantitative analysis of nonmigrating dHL-60 cells. Cells were defined as nonmigrating when there was no detectable movement of the uropod during the observed time period of at least 7 minutes. n = 29 (EGFP-Syk); n = 28 (EGFP-Syk K402R); n = 27 (EGFP-Syk Y348F). Analyzed cells were taken from 3 independent experiments. Means ± SD are shown. n.s. indicates not significant; *P < .02.