Extranuclear Apoptosis: The Role of the Cytoplasm in the Execution Phase

The execution phase is the “active” phase of apoptosis occurring immediately after a cell commits to the death program. It lasts about an hour and is characterized by the hallmark morphologic features of apoptosis (e.g., membrane blebbing, chromatin condensation, and DNA fragmentation) culminating with disassembly and packaging of the cell for phagocytosis. Most studies of the execution phase have focused on elucidating nuclear events with the identification of important mechanisms responsible for nuclear execution such as the link between release of cytochrome c, activation of caspase 9/3, and DNA fragmentation (Li et al. 1997; Liu et al. 1997; Enari et al. 1998). Study of cytoplasmic or extranuclear events, on the other hand, has lagged. However, within the past two years, insights into underlying mechanisms and biochemical regulation have led to greatly increased interest in...