Apoptosis: lessons from in vitro systems.

Although apoptosis is a major factor in metazoan morphogenesis and tissue homeostasis, its underlying biochemical mechanisms are poorly understood. This is now beginning to change as cell-free systems for the study of apoptosis start to reveal some of the activities involved. As suggested by earlier genetic analyses, a proteinase with properties resembling those of the interleukin-1-beta-converting enzyme (ICE) has been shown to initiate the apoptotic cascade in vitro. Curiously, results obtained with the cell-free systems suggest that essential downstream effectors of the apoptotic response may be intrinsic components of healthy nuclei.