The zebrafish YSL contains inducible apoptotic machinery. (A) Western blotting detection of cytochrome C from purified YSL mitochondria treated with tBid (20 nM) for increasing time durations (0–60 min). After treatment, mitochondria were pelleted by centrifugation; at 60 min, released cytochrome C due to outer membrane permeabilization was eventually found in the supernatant. The same western blot was probed with anti-F0/F1 ATPase antibody for calibration purpose (top panels). (B) Images of Mitotracker Red-stained embryos injected with control (left panel) or zBax mRNA (right panel). White arrowheads show YSL mitochondria location; zBax-injected embryos exhibit dramatic decrease of the labeling of the YSL mitochondria belt. (C) Immunostaining of activated caspase-3 in zBax-injected embryos (top panels). Embryos were counterstained with nuclear Hoescht33342. Nrz knock-down embryos coinjected with dextran-FITC were treated with ML-7 for 3 h prior staining (bottom panels). Active caspase-3 is mainly found in the YSL (white arrowheads).