The evolution of chromosomal instability in Chinese hamster cells: a changing picture?

Purpose: To investigate the kinetics of chromosomal instability induced in clones of Chinese hamster cells following X-irradiation. Materials and methods: X-irradiated clones of GM10115, human-hamster hybrid cells containing a single human chromosome 4 (HC4), have been previously e stablished. These clones were defined as unstable if they contained greater than or equal to three subpopulations of cells with unique rearrangements of HC4 as detected by FISH. Stable and unstable clones were analysed by FIS H and Giemsa staining at various times post-irradiation. Results: While most of the stable clones continued to show chromosomal stab ility of HC4 over time, one became marginally unstable at approximately 45 population doublings postirradiation. Clones exhibiting chromosomal instabi lity had one of several fates. Many of the unstable clones were showed simi lar levels of instability over time. However, one unstable clone became sta ble with time in culture, while another became even more unstable over time . Cytogenetic analyses of all clones after Giemsa staining indicated that i n some clones the hamster chromosomes were rearranged independent of HC4, d emonstrating increased frequencies of chromatid breaks and dicentric chromo somes. The majority of the unstable clones also had higher yields of chroma tid gaps. Conclusions: These data demonstrate the dynamic nature of chromosomal insta bility as measured by two different cytogenetic assays.