Intracellular localization of cyclin B1 during the cell cycle in glioma cells.

We investigated cyclin B1 expression during the cell cycle in human glioma cells cultured under asynchronous growing condition by two cytometry techniques: flow cytometry (FCM) and laser scanning cytometry (LSC). FCM analysis revealed the specific accumulation of cyclin B1 in G2/M phase with a wide intercellular variation (Dunphy WG: Trend Cell Biol 4:202-207, 1994). It is noteworthy that LSC, which is characterized by rapid quantitative analysis followed by imaging, allows morphological observation of the intracellular distribution of cyclin B1 as a function of cell cycle position cell by cell (Hunter T: Cell 75:839-841, 1993). Cyclin B1 was virtually undetectable in cells from G0/G1 phase to mid S phase, but became visible in the cytoplasm in late S phase. As cells proceeded within G2 phase, the level of cyclin B1 rapidly increased in the perinuclear region of the cytoplasm, but cyclin B1 was still faintly present in the nucleus. Cyclin B1 appeared in the nucleus at the mitotic phase. Then the nuclear membrane was disrupted and cyclin B1 was distributed evenly in the cell. The level of cyclin B1 was maximum in metaphase. However, it abruptly degraded at the end of metaphase, and subsequently G1 cells were cyclin B1 negative.