Separation of cells at different times within G2 and mitosis by cyclin B1 flow cytometry.

Multivariate flow cytometry using specific cyclin proteins and DNA content can identify cell populations at different points within the cell cycle. Quantification of cyclin B1 and DNA content reveals that cells with high levels of cyclin B1 predominantly have a 4C DNA content and are therefore in G2 or mitosis. We have examined whether separation of cells by levels of cyclin B1 could be used to discriminate cells at discrete times within these phases. Post-replicative cells progressively enter into fractions with higher levels of cyclin B1, indicating that this protein can be used as a marker of time in G2. Furthermore, cells in particular phases of mitosis can be greatly enriched by separation based on cyclin B1 levels. This method can thus be used to isolate cells at specific times within G2 and mitosis, periods of the cell cycle that have been difficult to study by cell fractionation.