Biological effects of low-dose γ-ray irradiation on chromosomes and DNA of Drosophila melanogaster.

While the damage to chromosomes and genes induced by high-dose radiation (HDR) has been well researched in many organisms, the effects of low-dose radiation (LDR), defined as a radiation dose of ≤100 mSv, are still being debated. Recent research has suggested that the biological effects of LDR differ from those observed in HDR. To detect the effect of LDR on genes, we selected a gene of Drosophila melanogaster, known as the multiple wing hair (mwh) gene. The hatched heterozygous larvae with genotype mwh/+ were irradiated by γ-rays of a 60Co source. After eclosion, the wing hairs of the heterozygous flies were observed. The area of only one or two mwh cells (small spot) and that of more than three mwh cells (large spot) were counted. The ratio of the two kinds of spots were compared between groups irradiated by different doses including a non-irradiated control group. For the small spot in females, the eruption frequency increased in the groups irradiated with 20-75 mGy, indicating hypersensitivity (HRS) to LDR, while in the groups irradiated with 200 and 300 mGy, the frequency decreased, indicating induced radioresistance (IRR), while in males, 50 and 100 mGy conferred HRS and 75 and 200 mGy conferred IRR. For the large spot in females, 75 mGy conferred HRS and 100-800 mGy conferred IRR. In conclusion, HRS and IRR to LDR was found in Drosophila wing cells by delimiting the dose of γ-rays finely, except in the male large spot.

Endoreduplication in Drosophila melanogaster progeny after exposure to acute γ-irradiation.

The purpose of this investigation was to study the effect of acute γ-irradiation of parent adults on the endoreduplication of giant chromosomes in F1 generation of Drosophila melanogaster Meig. A wild-type Oregon-R strain was used as the material. Virgin females and males of Drosophila adults at the age of 3 days were irradiated with doses of 8, 16 and 25 Gy. Giant chromosomes were studied by cytomorphometry on squashed preparations of Drosophila salivary glands stained with acetoorsein. The preparations were obtained at late third instar larvae. The mean values of the polyteny degree of chromosomes (PDC) in males increased after 8 Gy by 10.6%, after 25 Gy by 7.4%, and did not change after the dose of 16 Gy. In females, the PDC did not differ from the control irrespective of the irradiation dose. An increase in endoreduplication was also evidenced by the accelerated development of offsprings of both sexes after irradiation of parents with 25 Gy, and in males also at a dose of 16 Gy. The statistical impact of power of radiation on polyteny was 26.8%, while the impact of sex was 4.9%. The impact of power of radiation on the developmental rate of offspring was 4.4% in males and 7.5% in females. The enhancement of endoreduplication is considered as a consequence of increasing selection pressure after irradiation. The possible involvement of epigenetic effects in the effect of ionizing radiation on endoreduplication is discussed.

A new role for Drosophila Aurora-A in maintaining chromosome integrity.

Aurora-A is a conserved mitotic kinase overexpressed in many types of cancer. Growing evidence shows that Aurora-A plays a crucial role in DNA damage response (DDR) although this aspect has been less characterized. We isolated a new aur-A mutation, named aur-A949, in Drosophila, and we showed that it causes chromosome aberrations (CABs). In addition, aur-A949 mutants were sensitive to X-ray treatment and showed impaired γ-H2Av foci dissolution kinetics. To identify the pathway in which Aur-A works, we conducted an epistasis analysis by evaluating CAB frequencies in double mutants carrying aur-A949 mutation combined to mutations in genes related to DNA damage response (DDR). We found that mutations in tefu (ATM) and in the histone variant H2Av were epistatic over aur-A949 indicating that Aur-A works in DDR and that it is required for γ-H2Av foci dissolution. More interestingly, we found that a mutation in lig4, a gene belonging to the non-homologous end joining (NHEJ) repair pathway, was epistatic over aur-A949. Based on studies in other systems, which show that phosphorylation is important to target Lig4 for degradation, we hypothesized that in aur-A949 mutant cells, there is a persistence of Lig4 that could be, in the end, responsible for CABs. Finally, we observed a synergistic interaction between Aur-A and the homologous recombination (HR) repair system component Rad 51 in the process that converts chromatid deletions into isochromatid deletions. Altogether, these data indicate that Aur-A depletion can elicit chromosome damage. This conclusion should be taken into consideration, since some anticancer therapies are aimed at reducing Aurora-A expression.

Genetics and biology of Anastrepha fraterculus: research supporting the use of the sterile insect technique (SIT) to control this pest in Argentina.

Two species of true fruit flies (taxonomic family Tephritidae) are considered pests of fruit and vegetable production in Argentina: the cosmopolitan Mediterranean fruit fly (Ceratitis capitata Wiedemann) and the new world South American fruit fly (Anastrepha fraterculus Wiedemann). The distribution of these two species in Argentina overlaps north of the capital, Buenos Aires. Regarding the control of these two pests, the varied geographical fruit producing regions in Argentina are in different fly control situations. One part is under a programme using the sterile insect technique (SIT) for the eradication of C. capitata, because A. fraterculus is not present in this area. The application of the SIT to control C. capitata north of the present line with the possibility of A. fraterculus occupying the niche left vacant by C. capitata becomes a cause of much concern. Only initial steps have been taken to investigate the genetics and biology of A. fraterculus. Consequently, only fragmentary information has been recorded in the literature regarding the use of SIT to control this species. For these reasons, the research to develop a SIT protocol to control A. fraterculus is greatly needed. In recent years, research groups have been building a network in Argentina in order to address particular aspects of the development of the SIT for Anastrepha fraterculus. The problems being addressed by these groups include improvement of artificial diets, facilitation of insect mass rearing, radiation doses and conditions for insect sterilisation, basic knowledge supporting the development of males-only strains, reduction of male maturation time to facilitate releases, identification and isolation of chemical communication signals, and a good deal of population genetic studies. This paper is the product of a concerted effort to gather all this knowledge scattered in numerous and often hard-to-access reports and papers and summarize their basic conclusions in a single publication.

Characterization of TTAGG telomeric repeats, their interstitial occurrence and constitutively active telomerase in the mealybug Planococcus lilacinus (Homoptera; Coccoidea).

We confirmed the occurrence of the insect TTAGG telomeric repeats in the mealybug Planococcus lilacinus, a radiation-resistant coccid, by single primer polymerase chain reaction (PCR) and Southern hybridization. Analysis of Bal31 nuclease-digested DNA by Southern hybridization and chromosomes by FISH suggests that these repeats occur mainly at the ends of the chromosomes. However, sequence analysis of the PCR products of TTAGG-associated sequences from genomic DNA showed their interstitial occurrence and association with certain unrelated low-copy repeats. Because of their shorter length, the interstitial TTAGG sequences were detectable by primed in situ hybridizations but not by FISH. Analysis of chromosomes recovered after irradiation by fluorescent in situ hybridization suggested acquisition of TTAGG repeats at a majority of the healed ends. We also observed mild telomerase activity in unirradiated insects which was further enhanced after irradiation. Taken together, these results suggest that the mealybug has an efficient mechanism of formation of TTAGG repeats at radiation-induced chromosome ends and constitutively active telomerase may be a feature associated with rapid recovery of chromosome ends damaged by ionizing radiation.