Chromosome analysis of small and large L5178Y mouse lymphoma cell colonies: comparison of trifluorothymidine-resistant and unselected cell colonies from mutagen-treated and control cultures.

ABSTRACT

Mutagenesis assays at the thymidine kinase (TK) locus in L5178Y mouse lymphoma cells frequently yield mutant colonies with a bimodal size distribution. The objectives of this study were to determine whether a relationship exists between mutant colony size and chromosomal aberrations and whether the colony-size distributions obtained from this assay can indicate the clastogenic activity of a test chemical. Cells from 8 different types of L5178Y mouse lymphoma cell colonies were examined for chromosomal abnormalities within 10 cell generations after colony isolation. The colonies included small (sigma) and large (lambda) unselected cell (UC) and trifluorothymidine-resistant (TFTr) colonies derived from TK +/- cell cultures treated with the solvent dimethyl sulfoxide (DMSO) or hycanthone methanesulfonate (HYC). Chromosome abnormalities were present in cells from 12% (7/60) of the UC colonies, but there was no apparent relationship between colony diameter and the presence of chromosomal abnormalities. Abnormalities affecting chromosome 11, which is believed to be the site of the TK gene, were not observed in cells from UC colonies. Abnormalities affecting chromosome 11 were observed only in cells from sigma-TFTr colonies irrespective of whether they were spontaneous (5/15 colonies) or induced by HYC (4/15 colonies). Overall, 30% (9/30) of sigma-TFTr colonies had cells with an abnormal chromosome 11 and 10% (3/30) had abnormalities affecting other chromosomes. Abnormalities affecting chromosome 11 were not observed in cells from lambda-TFTr colonies (0/30 colonies). The observation of only 30% of sigma-TFTr colonies with chromosome damage affecting chromosome 11 indicates that other mechanisms, in addition to chromosome damage at the level of resolution used in this study (i.e., 200-300 chromosome bands). contribute to small TFTr colony size.