Purpose: To test the possible involvement of the XRCC2 gene in the control
of intra-versus interchromatid rearrangements leading to chromatid breaks i
n G(2) cells by studying the Colour-switch ratio (CSR) in harlequin-stained
Chinese hamster irs1 cells.
Materials and methods: The V79-1 mutant cell lines irs1 (XRCC2 mutation) an
d irs2 (XRCC8 mutation), two WT V79 lines and GT621-1 (irs1 transfected wit
h the XPLC2 gene) were labelled with BrdU through two cell cycles, irradiat
ed and sampled 1.5 h after exposure. Metaphase spreads were analysed for ch
romatid break frequency and frequencies of colour-switch (colour-switch bet
ween chromatids at the break point) and non-colour-switch breaks, from Whic
h the CSR was calculated.
Results: Chromatid breaks were induced linearly with dose in all lines, and
frequencies were elevated in irs1 and irs2 mutant Cell lines when Compared
with WT lines. An XRCC2 transfected line (GT621-1) showed full radiosensit
ivity complementation with respect to frequencies, of chromatid breaks. The
CSR was significantly higher in irs1 (13.9%) than in the parental V79-4 (7
.5%) or irs2 (4.9%) cells. GT621-1 cells showed partial, but significant co
mplementation with respect to CSR (9.2%).
Conclusions: It is concluded that the significantly higher CSR for the irs1
mutant than for the Wild-type parental V79-4 line indicates the involvemen
t of the XRCC2 gene product in the control of the rearrangement process lea
ding to chromatid breaks.