Cell Cycle Analysis by Flow Cytometry

Cell cycle is a series of events that takes place in cell duplication and disregulation of it may lead to tumor formation. So monitoring of cell cycle can provide much information for disease diagnosis and therapy prognosis.

G0 is a resting phase where the cell has left the cycle and has stopped dividing. Cell cycle can be devided to four phases as follows:

G1 phase: RNA, ribosomes and proteins are synthesized for preparation;
S phase: DNA is replicated;
G2 phase: During the gap between DNA synthesis and mitosis;
M phase: cells are divied into two daughter cells.

The principle of detection methods using flow cytometry

The principle of widely used detection methods using flow cytometry is DNA content differentiation in varies of phases. The ploidy of cells in G1, S, G2 and M is 2N, 2-4N, 4N and 4N, respectively. However, G0 and G1 phase, G2 and M phase, which both have an identical DNA content could not be discriminated based on their differences in DNA content.

Other methods have also been develped to detect cell cycle. One method based on the bivariate analysis of DNA content and proliferation-associated proteins, for exmaple, the expression of cyclin D, cyclin E, cyclin A, or cyclin B1. This approach can distinguish G0 from G1 cells, identify mitotic cells or relate expression of other intracellular proteins to the cell cycle phase. The other method relies on the detection of 5'-bromo-2'-deoxyuridine (BrdU) incorporation to label the DNA-replicating cells.