Postirradiation growth in HAT medium fails to eliminate the delayed appearance of 6-thioguanine-resistant clones in EJ30 human epithelial cells

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Abstract

The latent effects of radiation-induced damage include 'delayed' mutations that arise de novo in the progeny of nonmutant cells. We investigated the early stages of delayed mutagenesis at the HPRT locus of EJ30 human epithelial cells that were exposed to 4 Gy of 137Cs γ rays. To eliminate directly induced 'prompt' HPRT- mutants, cultures were grown in HAT medium before selection in 6-thioguanine was applied. Although irradiated cells were grown in HAT medium throughout the phenotypic expression period, mutant fractions some tenfold above spontaneous levels were observed subsequently; incubation in HAT medium did not cause an increase in mutations in unirradiated cells. We conclude that, in our experimental system, a significant proportion of induced mutation is of a delayed type. We speculate that the delayed induction is caused by an instability process that is a frequent and (typically) transient consequence of exposure of cells to ionizing radiation. The connection, if any, between this process and other manifestations of instability, including the acquisition of a 'mutator phenotype,' remains to be established.

Original languageEnglish (US)
Pages (from-to)171-178
Number of pages8
JournalRadiation Research
Volume149
Issue number2
DOIs
StatePublished - 1998

Fingerprint

Thioguanine
mutations
epithelial cells
Clone Cells
culture media
Epithelial Cells
clones
Hypoxanthine Phosphoribosyltransferase
Growth
cells
mutagenesis
Mutation
progeny
phenotype
loci
mutation
ionizing radiation
mutants
acquisition
Radiation Effects

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Radiology Nuclear Medicine and imaging
  • Biophysics
  • Radiation

Cite this

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title = "Postirradiation growth in HAT medium fails to eliminate the delayed appearance of 6-thioguanine-resistant clones in EJ30 human epithelial cells",
abstract = "The latent effects of radiation-induced damage include 'delayed' mutations that arise de novo in the progeny of nonmutant cells. We investigated the early stages of delayed mutagenesis at the HPRT locus of EJ30 human epithelial cells that were exposed to 4 Gy of 137Cs γ rays. To eliminate directly induced 'prompt' HPRT- mutants, cultures were grown in HAT medium before selection in 6-thioguanine was applied. Although irradiated cells were grown in HAT medium throughout the phenotypic expression period, mutant fractions some tenfold above spontaneous levels were observed subsequently; incubation in HAT medium did not cause an increase in mutations in unirradiated cells. We conclude that, in our experimental system, a significant proportion of induced mutation is of a delayed type. We speculate that the delayed induction is caused by an instability process that is a frequent and (typically) transient consequence of exposure of cells to ionizing radiation. The connection, if any, between this process and other manifestations of instability, including the acquisition of a 'mutator phenotype,' remains to be established.",
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T1 - Postirradiation growth in HAT medium fails to eliminate the delayed appearance of 6-thioguanine-resistant clones in EJ30 human epithelial cells

AU - Loucas, Bradford

AU - Cornforth, Michael

PY - 1998

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N2 - The latent effects of radiation-induced damage include 'delayed' mutations that arise de novo in the progeny of nonmutant cells. We investigated the early stages of delayed mutagenesis at the HPRT locus of EJ30 human epithelial cells that were exposed to 4 Gy of 137Cs γ rays. To eliminate directly induced 'prompt' HPRT- mutants, cultures were grown in HAT medium before selection in 6-thioguanine was applied. Although irradiated cells were grown in HAT medium throughout the phenotypic expression period, mutant fractions some tenfold above spontaneous levels were observed subsequently; incubation in HAT medium did not cause an increase in mutations in unirradiated cells. We conclude that, in our experimental system, a significant proportion of induced mutation is of a delayed type. We speculate that the delayed induction is caused by an instability process that is a frequent and (typically) transient consequence of exposure of cells to ionizing radiation. The connection, if any, between this process and other manifestations of instability, including the acquisition of a 'mutator phenotype,' remains to be established.

AB - The latent effects of radiation-induced damage include 'delayed' mutations that arise de novo in the progeny of nonmutant cells. We investigated the early stages of delayed mutagenesis at the HPRT locus of EJ30 human epithelial cells that were exposed to 4 Gy of 137Cs γ rays. To eliminate directly induced 'prompt' HPRT- mutants, cultures were grown in HAT medium before selection in 6-thioguanine was applied. Although irradiated cells were grown in HAT medium throughout the phenotypic expression period, mutant fractions some tenfold above spontaneous levels were observed subsequently; incubation in HAT medium did not cause an increase in mutations in unirradiated cells. We conclude that, in our experimental system, a significant proportion of induced mutation is of a delayed type. We speculate that the delayed induction is caused by an instability process that is a frequent and (typically) transient consequence of exposure of cells to ionizing radiation. The connection, if any, between this process and other manifestations of instability, including the acquisition of a 'mutator phenotype,' remains to be established.

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