Analysis of mutational effects at the HPRT locus in human G(0) phase lymphocytes irradiated in vitro with gamma rays

The mutational effects of ionising radiation at the hypoxanthine-guanine ph osphoribosyl transferase (HPRT) locus were studied in human peripheral bloo d G(0) phase lymphocytes irradiated in vitro with gamma rays. The presence of radiation induced mutants was assessed by selecting the HPRT mutants eve ry week on the basis of 6-thioguanine resistance up to 1 month after irradi ation. A dose-related increase of 14.25 x 10(-6) mutants/Gy was measured af ter an expression time of 7 days. After 2 weeks from culture starting the f raction of clonable cells in irradiated and control cell populations decrea sed, limiting the measurements of mutant frequency. The mutational spectrum of the HPRT gene was determined by PCR analyses in a total of 99 mutant cl ones derived from irradiated lymphocytes. The independent origin of mutant clones carrying the same mutation was assessed by analysing the TCR gamma g ene rearrangements. The results showed a dose-related increase of deletion mutants up to 3 Gy, whereas point mutation frequency increased only up to 2 Gy. Two preferentially deleted regions were identified; one involving the HPRT exon 3, and another one the 3'-terminal and the 3'-flanking region of the gene. One complex mutation involving a non-contiguous deletion of exons 2-5 and 7/8 was observed among the mutants isolated after 3 Gy irradiation . (C) 2001 Elsevier Science B.V. All rights reserved.