Figure 4.

Live single-cell imaging of caspase-3 activity in HeLa cells. (A) Merged images of HeLa cells transfected with C3-BRET sensor, 48 h after transfection. At the initiation of the experiment caspase activity was induced by the addition of staurosporine (STS, 5 μM) and images were recorded after 2 (left) and 4 h (right) (Scale bar = 20 μm). (B) Percentage of HeLa cells showing caspase activity (emission ratio <0.8) over time. (C) Bioluminescent images showing cleavage of single cells in two channels, Nluc emission (420–460 nm) and mNeonGreen (510–550 nm) emission, 4 h after STS addition. Scale bar = 20 μm. (D) Bioluminescent emission ratio traces of three cells labeled in (C) showing caspase-3 activation. Measurements were done at 37 °C and 5% CO₂ in Dulbecco’s modified Eagle’s Medium, supplemented with 10% fetal bovine serum, under humidifying conditions.