Measurement of DNA synthesis by flow cytometry

Cells were stained for DNA content with Hoechst 33258 combined with propidium iodide and analyzed on an epi-fluorescence flow cytometer. Scatterplots of red versus blue fluorescence of control cells showed a straight line indicating that both dyes were measuring proportional amounts of cellular DNA. Scatterplots of cells incubated with the thymidine analog bromodeoxyuridine, however, showed a displacement from the control straight line that increased with longer exposure time to bromodeoxyuridine. These results suggest that bromodeoxyuridine incorporation in DNA can be detected by flow cytometry.