Mutagen treatment of single Chinese hamster ovary cells produces colonies mosaic for glucose-6-phosphate dehydrogenase activity

Abstract

When populations of single Chinesee hamster ovary (CHO) cells were exposed to the mutagen ethyl methane sulfonate (EMS), allowed to grow into colonies, and stained for glucose-6-phosphate dehydrogenase (G6PD) activity, two types of unstained colonies were observed at a frequency of about on per thousand stained colonies. These negative-staining colonies consisted of (1) colonies uniformly deficient in staining activity (pure); and (2) colonies containing both stained and unstained sectors (mosaic) in various relative sizes and patterns. Unstained cells isolated from mosaic colonies were genetically stable and had significantly reduced or absent G6PD activity. Random cell aggregation or chromosome segregation from tetraploid cells is not a significant cause of the sectoring phenomenon. Also, mosaic colonies are not principally caused by mutation at one of two replicated G6PD genes and their subsequent segregation during division. The simplest explanation for this phenomenon is that EMS induces a mutational change in one of the two DNA strands and DNA replication then produces normal and mutant double-stranded DNAs which segregate into wild-type and G6PD-deficient cell types, producing a mosaic colony.

DNA damage, DNA repair, cell proliferation, and DNA replication: How do gene mutations result?

“…(Mutations induced in proliferating CHO cells by alkylating agents correlate with O 6 -G adducts and are primarily G:C3A:T transition mutations.) A novel in situ study of alkylation induced mutations at the glucose-6-phosphate dehydrogenase (G6PD) gene in CHO cells that allowed analysis of the mutant phenotype in single cell colonies showed both mosaic colonies, i.e., 50% mutant and 50% wild type, and pure colonies, i.e., 100% mutant (16,17). (The mosaic colonies are parallels to Bielas and Heddle's bacterial mutations, and the pure colonies parallel their cellular mutations.)…”

Mutation in G6PD gene leads to loss of cellular control of protein glutathionylation: Mechanism and implication

“…The clones were selected by histochemical stain for G6PD enzyme activity [Stamato et al, 1982]. The E89 clones were found to have no functional enzyme activity.…”