Flow cytofluorimetric measurement of incorporated bromodeoxyuridine, using a double-stained cell population, allows the determination of the distribution of cells along the cell cycle (1). We have developed a simple computer program for the direct treatment of 64 x 64 channel histograms. This analysis appears to provide interesting data about the distribution of cells in the various phases of the cell cycle, namely the S phase.Two examples have been chosen to illustrate possible fields for the application of such a program. Comparison of two cell lines such as friend murine erythroleukemia cells (MELC) and fibroblasts FR3T3 cells has shown that this analysis can be used for cellcycle characterization of a given cell line.The program also allows the differential analysis of cell distribution along the cell cycle as a function of a given parameter. This possibility has been applied to study the vari- Flow cytofluorimetry has proved to be a reliable technique to measure rapidly, and with only minor perturbation of the cells, the distribution of a cell population along the cell cycle. Usually cell-cycle parameters are obtained from DNA histograms recorded from cells stained with a single dye, such as ethidium, propidium iodide, or other DNA-specific dyes. Computer methods (2, 3, 5) have been developed in order to deconvolve the histograms into their three basic components: the number of cells in the G1, S, and G2 + M phases.Nevertheless, these methods are based on the use of mathematical models and do not provide a physical means to distinguish cells belonging t o G1 from those belonging to early S and the G2 + M cells from the late S population.Recently, antibromodeoxyuridine monoclonal antibodies have been produced (7') and used in flow cytofluorometry to measure the incorporated BrdUrd. In order to improve this method, double-staining procedures have been developed using anti-BrdUrd antibodies to stain S cells labelled by BrdUrd in culture and conventional DNA staining to visualize GI and G2 + M cells (1, 4).Taking into account the good resolution of this staining procedure, we used the recorded data corresponding to such a double-stained cell population to establish the distribution of cells in a given phase of the cell cycle. This analysis is based on counting labelled or unlabelled cells, channel by channel, along the DNA scale.Such an analysis improves the quantitative treatment of data obtained by flow cytofluorimetry in two ways: ~ Address reprint requests to Jean-Jacques Lawrence, DRFBMCC,
The regulation of histone H1O content throughout the cell cycle of non‐synchronized Chinese hamster ovary (CHO) cells has been studied using double fluorescent staining and flow cytofluorometry. In exponentially growing cells, the amount of H1O was found to be proportional to the DNA content of the cells, indicating that the protein is synthesized throughout the cell cycle. However, when cells were arrested in G1 at saturation density the amount of H1O was greater than that found in G1 cells of the exponentially growing population. In contrast, the levels of H1‐1 were the same for G1 cells of both populations. These results show that the regulation of H1O accumulation differs from that of other histones.
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