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Human cells (HeLa) undergoing apoptosis after exposure to TNF. These cells express cytochrome fused to green fluorescent protein (GFP). After treatment, cytochrome-GFP (green) moves from mitochondria to the cytosol. The cells round, then bleb and externalize phosphatidylserine, identified by association with annexin V (red). Finally, a DNA dye (blue) stains the nuclei after the collapse of plasma-membrane integrity.