[Radiation biology of structurally different Drosophila genes. Report 2. The vestigial gene: molecular characteristics of chromosome mutations].

The results of the PCR-assay of mutation lesions at each of 16 fragments overlapping the entire vestigial (vg) gene of Drosophila melanogaster in 52 gamma-ray-, neutron- and neutron + gamma-ray-induced vg mutants having the inversion or translocation breakpoint within the vg microregion are presented. 4 from 52 mutants studied were found to have large deletions of about 200 kb covering the entire vg gene and adjacent to sca and l(2)C gene-markers as well. 23 mutants from 48 (47.9%) were found to have a wild-type gene structure showing that the exchange breakpoints are located outside of the vg gene. 25 others display the intragenic lesions of different complexity detected by PCR as the absence of(i) either one fragment or (ii) two or more (6-7) adjacent fragments and (iii) simultaneously several (i) or (i) and (ii) types separated by normal gene regions. It is important that 6 from 25 mutants have the breakpoint inside the vg gene and display the (i) or (ii) type of lesions at the gene regions containing the putative break whereas 5 others from 25 with the above lesions have the exchange breakpoint outside the vg gene. Therefore, the breakpoints underlying either inversions or translocations induced by low- and high-LET radiation are likely to be located within and outside the gene under study. Thereby, the formation of exchanges is accompanied by DNA deletions of various sizes at the exchange breakpoints. The molecular model of formation of such exchange-deletion rearrangements is elaborated and presented. Also, conception of the predominately clustered action of both low- and high-LET radiation on the germ cell genome is suggested as the summing-up of the presented results. The ability of ionizing radiation to induce the clusters of genetic alterations in the form of hidden DNA damages as well as gene/chromosome mutations is determined by the track structure and hierarchical organization of the genome. To detect the quality and frequency patterns of all components of the cluster, joint molecular, genetic and cytological techniques need to be used.

[Molecular genetics of radiation-induced chromosome breaks in a gene area in Drosophila: "position" effect of gene mutation?]. / Molekuliarnaia genetika radiatsionno-indutsirovannykh khromosomnykh razryvov v oblasti gena u Drosophila: "éffekt polozheniia" ili mutatsii gena?

On the sample of 43 gamma-ray and neutron-induced inversion or translocation exchanges with the vestigial (vg) phenotype, the molecular cytogenetic analysis of distribution of exchange breakpoints on the molecular map of Drosophila vg region (subsection 49D3-4 on the polytene chromosome 2R) was performed using hybridisation in situ technique. Simultaneously, PCR-assay of DNA alterations in all exons and introns (except for intron 4) of the vg gene for 18 mutants with exchange breakpoints outside of the gene was carried out. The results obtained by these molecular genetic techniques have shown that 1) radiation-induced breaks under chromosome exchanges with the vg phenotype were regularly located inside of the vg gene (19 cases out of 43 studied ones or 44.2%) passing through the large introns; 2) breakpoints were frequently flanked by deletions of the gene as whole (3 exchanges) or of its major part (3 exchanges); 3) many of the breaks (18/43 or 41.8%) are situated outside (distal or proximal) of the gene although such mutants have got the vg phenotype; 4) 2/3 (12/18 or 66.7%) vg mutants with the breakpoint outside of gene show the intragenic DNA lesions (microdeletions, microinversions) occurring obviously independently and simultaneously with the neighbor chromosome breaks; 5) only each third vg mutant with break outside of the gene (6/18 or 33.3%) have the unchanged gene subregions under study and presents obviously the result of "position effect" which appear to manifest itself for a distance of 2-30 kb (more near and farther locations of the proximal and distal breakpoints, respectively, relative to the vg gene). Our findings showing regular induction of the multiple genetic lesions (chromosome breaks and mutations of the adjacent genes) on the both ends of chromosome exchange induced by single track produced by gamma-rays or neutrons were discussed as a scientific basis for the conceptually new approaches to the assessment of both genetic damage numbers in the cell genome with chromosome exchange (the multiple genetic lesions) and radiation genetic risk (our molecular genetic approach showing the need for an increase of risk levels at least on a factor of 3 for the heritable chromosome alterations detected by the ordinary cytogenetic monitoring).

[Relative genetic effectiveness of fission neutrons in inducing various types of recessive mutation in Drosophila melanogaster]. / OGE neitronov deleniia pri induktsii retsessivnykh mutatsii raznogo tipa u Drosophila melanogaster.

The RCR-analysis of 53 gamma-Ray- and neutron-induced vg recessive mutations of Drosophila melanogaster combined with complementation assay with the vg[nw83b27] deletion mutation is used to detect precisely the RGE values of neutrons (0.85 MeV) under the chromosome and point (at the DNA level) mutation induction. Simultaneously, the induction-kinetics of gamma-ray- and neutron-induced macrodeletion as well as recessive lethal mutations in the X-chromosome were studied. The results obtained have shown that all genetic end-points increase linearly with gamma-ray or neutron dose. Thereby, the efficacy of neutrons is found to be twice (and more) as large as that of gamma-rays under the all macro- and micro-aberration mutation induction (macrodeletions and recessive lethals in the X-chromosome, multilocus deletions and intragenic deletions as well). Unlike that, the RGE of neutrons are more than twice as low as that of gamma-rays under the gene/point mutation induction. This feature of neutrons have been predicted as far back as in the early days of the radiation genetics (N.W. Timofeeff-Ressovsky, K.G. Zimmer, 1938), but experimentally supported at the DNA level just now.