Influence of homologous recombinational repair on cell survival and chromosomal aberration induction during the cell cycle in γ-irradiated CHO cells

Paul F. Wilson, John M. Hinz, Salustra S. Urbin, Peter B. Nham, Larry H. Thompson

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The repair of DNA double-strand breaks (DSBs) by homologous recombinational repair (HRR) underlies the high radioresistance and low mutability observed in S-phase mammalian cells. To evaluate the contributions of HRR and non-homologous end-joining (NHEJ) to overall DSB repair capacity throughout the cell cycle after γ-irradiation, we compared HRR-deficient RAD51D-knockout 51D1 to CgRAD51D-complemented 51D1 (51D1.3) CHO cells for survival and chromosomal aberrations (CAs). Asynchronous cultures were irradiated with 150 or 300 cGy and separated by cell size using centrifugal elutriation. Cell survival of each synchronous fraction (∼20 fractions total from early G1 to late G2/M) was measured by colony formation. 51D1.3 cells were most resistant in S, while 51D1 cells were most resistant in early G1 (with survival and chromosome-type CA levels similar to 51D1.3) and became progressively more sensitive throughout S and G2. Both cell lines experienced significantly reduced survival from late S into G2. Metaphases were collected from every third elutriation fraction at the first post-irradiation mitosis and scored for CAs. 51D1 cells irradiated in S and G2 had ∼2-fold higher chromatid-type CAs and a remarkable ∼25-fold higher level of complex chromatid-type exchanges compared to 51D1.3 cells. Complex exchanges in 51D1.3 cells were only observed in G2. These results show an essential role for HRR in preventing gross chromosomal rearrangements in proliferating cells and, with our previous report of reduced survival of G2-phase NHEJ-deficient prkdc CHO cells [Hinz et al., DNA Repair 4, 782-792, 2005], imply reduced activity/efficiency of both HRR and NHEJ as cells transition from S to G2.

Original languageEnglish (US)
Pages (from-to)737-744
Number of pages8
JournalDNA Repair
Issue number7
StatePublished - Jul 1 2010
Externally publishedYes



  • Cell cycle
  • Chromosomal aberrations
  • Complex exchange
  • Homologous recombinational repair
  • Non-homologous end-joining
  • Radiosensitivity

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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