Rapid cell cycle analysis. II. Phase durations and dispersions from computer analysis of RC curves

In this paper, we present a procedure for the rapid, quantitative estimation of the G1, S, and G2 + M phase durations and dispersions and the growth fraction for asynchronously growing cell populations. In this procedure, the cell population is pulse-labelled with a radioactive DNA precursor at the beginning of the analysis and then sampled periodically. The samples are dispersed, stained with a DNA specific dye, and processed through a cell sorter where cells from mid-S phase and G1 phase are sorted. The radioactivity per cell (RC) is determined for each sorted sample. In addition, the variation in the rate of incorporation of the radioactive DNA precursor across S phase is determined and the fractions of cells in the G1, S, and G2 + M phase are estimated from DNA distributions measured during sorting. We also describe an automatic computer analysis procedure for estimation of the G1, S, and G2 + M phase durations and dispersions and growth fraction by simultaneous analysis of the variations with time in the radioactivity per cell in G1 (RCG1) and radioactivity per cell in mid-S phase (RCS) curves, the G1, S, and G2 + M phase fractions and the variation in the rate of incorporation of radioactive DNA precursor uptake across S phase. The experimental and analytical aspects of the RC procedure are applied in the cell cycle analysis of Chinese hamster M3-1 cells grown in vitro. The parameters estimated by RC analysis agree well with similar parameters estimated by fraction-of-labelled-mitoses analysis.