Cell Cycle

The cell cycle refers to the whole process of a cell undergoing from the completion of one division to the end of the next, and the cell cycle is divided into two phases, interphase and mitosis.

The regulation of the cell cycle is mainly achieved by the arrest in the G1 phase. G0 phase refers to the state in which cells are in the arrest. Cells are divided in M phase, some can continue to divide for cycle cycling, and some jump into G0 phase to arrest. The G0 phase is a phase away from the cell cycling which temporarily stops dividing. But upon certain stimulation, the cell can again enter the cell cycle, synthesize DNA and undergo division.

The G0 phase is characterized by: ① unstimulated G0 cells, where the potential for DNA synthesis and cell division remains, and ② when G0 cells are stimulated to proliferate, they can synthesize DNA and undergo cell division.

Propidium iodide (PI) is a fluorescent dye that can be integrated into and bound to base pairs of double-stranded DNA and RNA with no base specificity. PI can produce fluorescence after binding to double-stranded DNA, and the fluorescence intensity and the content of double-stranded DNA are directly proportional. After the DNA inside the cells is stained with PI, the cells can be measured by flow cytometry for DNA content, and then, depending on the distribution of DNA content, analysis of the cell cycle can be performed.

Due to the different DNA content in each phase of the cell cycle, generally, normal cells have a DNA content (2n) of diploid cells in the G1 / G0 phase, and in G2 / M phase cells have a DNA content (4N) of tetraploid cells, and in S phase, the DNA content of the cells is between diploid and tetraploid. PI can bind to DNA, and its fluorescence intensity directly reflects the intracellular DNA content. Therefore, when the intracellular DNA content is examined by flow cytometry combined with PI staining, each phase of the cell cycle can be distinguished into G1 / G0, S, and G2 / M phases. The obtained flow histograms corresponding to each cell cycle can be analyzed by special software and therefore the cell% on each cell cycle can be calculated.