45. Radiation-Induced Mitotic Recombination in Human Lymphoblastoid Cells

Kouichi Tatsumi, Yuko Hoki, Akira Fujimori, Ikuko Furuno-Fukushi and Akira Tachibana^*
(^*Kyoto Univ., Radiation Biology Center)

Keywords: allelic loss, LOH, crossing-over, deletion, breakpoint

A selectable mutation assay accompanying the real-time detection PCR was developed to analyse the second step in loss-of-function mutations, employing a human lymphoblastoid cell line (LCL) derived from an obligate heterozygote of 2,8-dihydroxyadenine urolithiasis, adenine phosphoribosyltransferase (APRT) deficiency. The proportions of mutant clones with loss of heterozygosity (LOH) for spontaneous mutations and those induced by 2 Gy of gamma-rays were 68 % and 92%, respectively. Determination of the gene dosage revealed that about one half of the spontaneously arising mutant clones and two-thirds of those induced by gamma-rays showed reduction to homozygosity of the constitutionally inactivated APRT allele. The breakpoints of mitotic recombinations and deletions were not distributed randomly, but clustered at the border of the paracentromeric heterochromatin region of the chromosome 16. In an ataxia telangiectasia (AT) cell subline in which a new inactivation mutation had been introduced into an APRT allele by the treatment with ICR-191, mitotic recombination rarely occurred and deletion predominated in spontaneous and X-ray induced APRT mutations (Table 5).