Apoptosis Detection Assays

Many apoptosis assays are available since there are many proteins regulated at multiple points and involved in apoptosis signaling cascade. To detect apoptosis accurately, two or more assays should be used since there are many overlapped features between apoptosis and necrosis. There are six major groups of available assays to detect apoptosis: membrane alteration, mitochondrial assays, cytomorphological alterations, DNA fragmentation, detection of caspase, cleaved substrate, inhibitors and regulators, and detection of apoptosis in whole mounts. Among those assay, early apoptosis could be detected through annexin V, which is based on the loss of the cellular membrane integrity. Also, there are many assays that can detect midphase of apoptosis using caspase activation and molecular processing including PARP degradation. Late phase of apoptosis could be detected with DNA fragmentation assays. Combinations of these assays allow us to identify the mechanisms of apoptosis induction after specific stimulus. This chapter will introduce three apoptosis detection assays including annexin assay, DNA/chromatin condensation assays, and TUNEL assay.