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

Abstract

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 established. These clones were defined as unstable if they contained three sub-populations of cells with unique rearrangements of HC4 as detected by FISH. Stable and unstable clones were analysed by FISH and Giemsa staining at various times post-irradiation. Results: While most of the stable clones continued to show chromosomal stability of HC4 over time, one became marginally unstable at approximately 45 population doublings postirradiation. Clones exhibiting chromosomal instability had one of several fates. Many of the unstable clones were showed similar levels of instability over time. However, one unstable clone became stable with time in culture, while another became even more unstable over time. Cytogenetic analyses of all clones after Giemsa staining indicated that in some clones the hamster chromosomes were rearranged independent of HC4, demonstrating increased frequencies of chromatid breaks and dicentric chromosomes. The majority of the unstable clones also had higher yields of chromatid gaps. Conclusions: These data demonstrate the dynamic nature of chromosomal instability as measured by two different cytogenetic assays.