Bromodeoxyuridine (BrdUrd) is a thymidine analog, and can be labeled with anti-BrdUrd monoclonal antibodies conjugated to a fluorochrome. Together with propidium iodide (PI, a fluorescent DNA stain), this combination directly discriminates three phases of cell cycle (G0/G1, S, and G2/M) without the need for mathematically modeling. When cells are pulse-labeled with BrdUrd, cell cycle parameters can be determined.
In this example, Dr. Joseph Fontana investigates the S-phase arrest of normal mammary epithelial cells (see reference below). Pictured above is untreated cells labeled with anti-BrdUrd antibody conjugated to fluorescein isothiocynate (FITC) counterstained with propidium iodide (PI) for DNA content. Under the culture conditions, a large number of cells are proliferating, as can be seen by the large S-, G2-, and M-phase cell populations. Only the S-phase cells have incorporated BrdUrd, allowing easy enumeration of the S-phase fraction.
Zhang, Y., Rishi, A., Dawson, M., Tschang, R., Farhana, L., Boyanapalli, M., Reichert, U., Shroot, B., Van Buren, E., Fontana, J. S-phase arrest and apoptosis induced in normal mammary epithelial cells by a novel retinoid. Cancer Res. 60: 2025-32, 2000.