Figure 7. Dependence of cell fusion activity on cell surface density of VAMP1.

(A) v-cells were cotransfected with tTA (1 µg per 10 cm² growth area) and increasing amount of the flipped VAMP1 plasmid (per 10 cm² growth area): 0.01, 0.02, 0.05, 0.1, 0.2 and 0.5 µg. After the v-cells were combined with the t-cells expressing syntaxin1/SNAP-25 for 24 h, cell fusion was quantified. In parallel experiments, the expression level of VAMP1 proteins at surface of the v-cells was determined by staining with the anti-Myc antibody and FACS analysis. A polynomial regression curve was generated to model the relationship between cell fusion activity (OD₄₂₀) and mean fluorescence intensity of VAMP1 staining. Error bars represent standard deviation of three independent experiments. (B) Log-log plot of cell fusion activity vs. mean fluorescence intensity of VAMP1 staining. The solid line shows a linear regression, which yields a slope of 0.52 with a correlation coefficient of 0.901.