Mitochondria participate in apoptosis through a range of mechanisms that vary between vertebrates and invertebrates. In vertebrates, they release intermembrane space proteins, such as cytochrome c, to promote caspase activation in the cytosol. This process is the result of the loss of integrity of the outer mitochondrial membrane caused by proapoptotic members of the Bcl-2 family. This event is always accompanied by a fissioning of the organelle. Fission of mitochondria has also been reported to participate in apoptosis in Drosophila and Caenorhabditis elegans. However, in these organisms, mitochondrial membrane permeabilization does not occur and the mechanism by which mitochondrial dynamics participates in cell death remains elusive.