Quantitative analysis of cell cycle progression of synchronous cells by flow cytometry

Chinese hamster ovary (CHO) cells were synchronized by the mitotic selection procedure and their subsequent progression through the cell cycle was monitored by flow cytometry. It is shown that our previously proposed method for DNA histogram analysis is applicable even to highly synchronous cell populations lacking significant G1 and G2/M components, provided an appropriate control is used as a reference standard. We have also obtained estimates of cell cycle parameters from the DNA histograms in this system, including phase durations, relative cellular DNA synthesis rates as a function of position in S, and synchrony indices. In particular, the rate of DNA synthesis appears to be very low in early S phase in this cell line, giving rise to an unexpected early S phase peak in the histogram of asynchronous, exponentially growing cells.