The nature of gene mutations induced by ionizing radiation in germ cells and transmitted to offspring remains one of the most important problems in radiation genetics of higher eukaryotes. The data accumulated in this field were obtained by different authors under different experimental conditions which does not give a complete insight about the nature of radiation-induced inherited mutations at different genome levels (chromosome, gene, DNA). We obtained new data in this field under the same experimental conditions for five different genes. This first allow us to get a fairly complete picture of the spectrum and frequency of inherited recessive gene mutations in Drosophila melanogaster sperm cells exposed to γ-rays and neutrons. The spectra of genetic alterations underlying inherited recessive gene mutations for γ-rays and neutrons closely coincide and can be divided into two main classes: (i) mutations associated with chromosomal aberrations of different types (so-called gene/structural mutations) and (ii) point intragenic mutations (gene/point mutations) having DNA changes of different nature. Substantially, neutrons are 2.5 times more efficient than γ-rays in induction of the gene/structural mutations (4.1 and 1.6 E-0.6 / locus / Gy, respectively). In the gene/point mutations induction, the efficiency of two radiation studied is almost the same (1.2 and 1.1 E-0.6 /locus/Gy for neutrons and γ-ray, respectively). Precise PCR assay of the gene/point mutations allows us to identify two main classes of these mutations: (i) mutations with DNA changes not detected by this method (PCR+ mutants) and (ii) a group of mutants with intragenic deletions of different sizes and localization, including mutants with clusters of such independent deletions. Further sequence analysis of γ-ray-induced PCR+ black mutations made it possible to identify variety of DNA changes among which base substitutions are predominant mutation lesions (45%) while vast majority (90%) of neutron-induced mutations had changes in the form of the gene conversion event. The significance of a new molecular data obtained (clusters of DNA changes within the gene and in one turn of the DNA double-stranded helix, gene conversion) for a better understanding of the fundamental mechanisms of radiation mutagenesis and for assessment of genetic hazard (risk) of ionizing radiation at the molecular level is discussed.
Neutrons, γ-rays, Drosophila melanogaster, Locus-specific mutations, Chromosomal aberrations, Point mutations, PCR assay, Sequencing