Fig. 1. BCR-mediated SRF activation requires Lyn, Syk, Btk and PLCγ₂. (A) WT DT40 B cells were transiently transfected with SRF– luciferase reporter plasmid along with empty vector, or increasing concentrations of plasmid carrying dominant negative SRF (SRFpm1, 10 and 20 µg DNA). The cells were then either stimulated with anti-IgM (black bar) or left unstimulated (open bar) then lysed for luciferase assay. *P < 0.05 versus empty vector control. (B) SRF transcriptional activity was determined in WT and mutant DT40 cells lacking Lyn, Syk, Btk and PLCγ₂. The cells were either stimulated with anti-IgM (black bars), 10 ng/ml PMA/100 nM ionomycin (gray bars) or left unstimulated (open bars). *P < 0.05 versus WT cells. (C) Lipase activity of PLCγ is required for activation of SRF. SRF transcriptional activity was determined in PLCγ^–/– DT40 cells transfected with empty vector, WT PLCγ, or lipase-deficient PLCγ, followed by stimulation with anti-IgM.