Double staining of nuclei (DAPI blue) and mitochondria (JC-1). Left panel: control cells with intact nuclei, where JC-1 aggregates inside healthy mitochondria and fluoresces red (arrows). Right panel: apoptotic HT1376 bladder cancer cells with fragmented nuclei, where the monomeric form of JC-1 diffuses into the cytoplasm and fluoresces green (arrows). Cells in the right panel were treated with docetaxel (1 hour followed by a 96-hour wash-out). The aggregation of JC-1 in the mitochondria is driven by the transmembrane potential. Aggregated extracellular dye deposits (stars) are artifactual.