FIGURE 5.

FGFRL1ΔCΔ12 rapidly fuses HEK293 and CHO-PgsA cells and induces apoptotic cell death. A, kinetics of the FGFRL1-induced cell-cell fusion. HEK293 cells were transfected with FGFRL1ΔCΔ12-eGFP and seeded together with CHO-PgsA cells. The time of initial attachment was taken as the starting point. The figure displays snapshots taken every 40 min after the initial attachment of the cells. The first syncytial, multinucleated cells appeared after 40 min and rapidly expanded until, after 160 min, the entire field of vision was one continuous syncytium. 24 h after the onset of fusion, cells detached and appeared to be dying. Bar, 100 μm. B, activity of caspase 3/7 in the fusing HEK293 and CHO-PgsA cells. A luminometric caspase 3/7 activity kit was used to determine the activity of these effector caspases in the fusing cells. The asterisks indicate significant (p < 0.05) increases in caspase activity relative to unfused cells.