Multiplex polymerase chain reaction-based deletion analysis of spontaneous, gamma ray- and alpha-induced hprt mutants of CHO-K1 cells

Independent Chinese hamster ovary (CHO)-K1 cell mutants at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus were isolated from untreated, ⁶⁰Co γ ray-and ²¹²Bi α-exposed cells and the genetic changes underlying the mutation determined by multiplex polymerase chain reaction (PCR)-based exon deletion analysis. In the 71 spontaneous mutants analyzed, 77.5% of the clones showed no change in exon number or size, 15.5% showed a loss of a single exon, 4.2% showed a loss of 2-8 exons, and 2.8% showed loss of all nine hprt exons (total gene deletion). Exposure to 6 Gy of γ rays, which reduced survival levels to 10%, produced a significantly different deletion spectrum that was shifted toward deletions with 45% of the 20 mutants analyzed showing a loss of a single exon and 30% showing a loss of all nine exons. Exposure to 2 Gy α radiation from ²¹²Bi, a ²²⁰Rn daughter, a dose which also reduced survival levels to about 10%, resulted in a deletion spectrum similar to the γ-ray spectrum in that more than 75% of the 49 mutants analyzed were deletions. The α spectrum, however, was significantly different from both the spontaneous and γ spectra with 55.1% of the α mutants showing a loss of all nine exons, 10.2% showing loss of a single exon, and 14.3% showing loss of 2-8 exons. Thus, α-radiation appears to produce larger intragenic deletions than γ radiation. The results suggest that intragenic deletion size should be considered when low- and high linear energy transfer (LET) mutation spectra are compared.