Cell cycle analysis

Cell cycle analysis by DNA content measurement is a method that most frequently employs flow cytometry to distinguish cells in different phases of the cell cycle. Before analysis, the cells are and treated with a fluorescent dye that stains DNA quantitatively, such as propidium iodide (PI) or 4,6-diamidino-2-phenylindole (DAPI). The fluorescence intensity of the stained cells correlates with the amount of DNA they contain. As the DNA content doubles during the S phase the DNA content (and thereby intensity of fluorescence)of cells in the G₀ phase and G₁ phase (prior to-S), in the S phase, and in the G₂ phase and M phase (post-S) identifies the cell cycle-phase position in the major phases (G₀/G₁ versus S- versus G₂/M phase) of the cell cycle. The cellular DNA content of individual cells is often plotted as their frequency histogram which then is deconvoluted by the respective computer algorithms to provide information about relative frequency (percentage) of cells in the major phases of the cell cycle.

Cell cycle anomalies revealed on the DNA content frequency histogram are often observed after different types of cell damage, for example such DNA damage that interrupts the cell cycle progression at certain checkpoints. Such an arrest of the cell cycle progression can lead either to an effective DNA repair which may prevent transformation of normal into a cancer cell (carcinogenesis), or to cell death, often by the mode of apoptosis. An arrest of cells in G_0< or G₁ is often seen as a result of lack of nutrients (growth factors), for example after serum deprivation. Cell cycle analysis was first described in 1969 at Los Alamos Scientific Laboratory by a group from the University of California using the Feulgen staining technique. The first protocol for cell cycle analysis using propidium iodide staining was presented in 1975 by Awtar Krishan from Harvard Medical School and is still widely cited today.

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