Schematic overview of markers for detection of proliferation and apoptosis. (A) Markers for detection of proliferation include Ki-67, MCM-2, and proliferating cell nuclear antigen (PCNA); quantification of DNA content using intercalating DNA dyes such as propidium iodide (PI) and DRAQ5; and immunostaining for incorporated 5-bromo-2′-deoxyuridine (BrdU), 5-iodo-2′-deoxyuridine (IdU), and 5-ethynyl-2′-deoxyuridine (EdU). (B) Markers for detection of apoptosis include annexin V, DNA fragmentation as determined by the terminal deoxynucleotidyltransferase (TdT)–mediated dUTP nick end labeling (TUNEL) assay, FAS detection, and detection of members of the Bcl-2 protein family or caspase activation.