Oxidative and radiation stress induces transposable element transcription in Drosophila melanogaster.

It has been shown that stressors are capable of activating transposable elements (TEs). Currently, there is a hypothesis that stress activation of TEs may be involved in adaptive evolution, favouring the increase in genetic variability when the population is under adverse conditions. However, TE activation under stress is still poorly understood. In the present study, we estimated the fraction of differentially expressed TEs (DETEs) under ionizing radiation (144, 360 and 864 Gy) and oxidative stress (dioxin, formaldehyde and toluene) treatments. The stress intensity of each treatment was estimated by measuring the number of differentially expressed genes, and we show that several TEs families are activated by stress whereas others are repressed. The proportion of DETEs was positively related to stress intensity. However, even under the strongest stress, only a small fraction of TE families were activated (9.28%) and 17.72% were repressed. Considering all treatments together, the activated proportion was 19.83%. Nevertheless, as several TEs are incomplete or degenerated, only 10.55% of D. melanogaster mobilome is, at same time, activated by the stressors and able to transpose or at least code a protein. Thus, our study points out that although stress activates TEs, it is not a generalized activation process, and for some families, the stress induces repression.

Sexually dimorphic DNA damage responses and mutation avoidance in the mouse germline.

Germ cells specified during fetal development form the foundation of the mammalian germline. These primordial germ cells (PGCs) undergo rapid proliferation, yet the germline is highly refractory to mutation accumulation compared with somatic cells. Importantly, while the presence of endogenous or exogenous DNA damage has the potential to impact PGCs, there is little known about how these cells respond to stressors. To better understand the DNA damage response (DDR) in these cells, we exposed pregnant mice to ionizing radiation (IR) at specific gestational time points and assessed the DDR in PGCs. Our results show that PGCs prior to sex determination lack a G1 cell cycle checkpoint. Additionally, the response to IR-induced DNA damage differs between female and male PGCs post-sex determination. IR of female PGCs caused uncoupling of germ cell differentiation and meiotic initiation, while male PGCs exhibited repression of piRNA metabolism and transposon derepression. We also used whole-genome single-cell DNA sequencing to reveal that genetic rescue of DNA repair-deficient germ cells (Fancm-/- ) leads to increased mutation incidence and biases. Importantly, our work uncovers novel insights into how PGCs exposed to DNA damage can become developmentally defective, leaving only those genetically fit cells to establish the adult germline.

[Effects of Chronic Irradiation at Low Doses on Morphological Indicators of Reproductive System of Dysgenic Female Drosophila melanogaster].

In this paper the contribution of chronic irradiation at low doses (0.42 mGy/h) and dysgenesis to changing morphological parameters (gonadal atrophy/sterility and ovarian reserve) of the reproductive system of female Drosophild melanogaster is rated. It is shown that the sterilizing effect of dysgenesis is enhanced predominantly by irradiation of the maternal line. The level of ovarian reserve of irradiated females depends on the type of dysgenic system. Unlike I-R females in whom the level of radiation-induced ovarian reserve does not differ from the control, both decrease (in P-M females) and increase (in H-E females) is observed in the ovariole number. The results indicate the important role of mobile genetic elements destabilizing the genome in the modification of reproductive functions of females exposed to chronic-action of low-intensity γ-radiation.

Response of transposable elements to environmental stressors.

Transposable elements (TEs) comprise a group of repetitive sequences that bring positive, negative, as well as neutral effects to the host organism. Earlier considered as "junk DNA," TEs are now well-accepted driving forces of evolution and critical regulators of the expression of genetic information. Their activity is regulated by epigenetic mechanisms, including methylation of DNA and histone modifications. The loss of epigenetic control over TEs, exhibited as loss of DNA methylation and decondensation of the chromatin structure, may result in TEs reactivation, initiation of their insertional mutagenesis (retrotransposition) and has been reported in numerous human diseases, including cancer. Accumulating evidence suggests that these alterations are not the simple consequences of the disease, but often may drive the pathogenesis, as they can be detected early during disease development. Knowledge derived from the in vitro, in vivo, and epidemiological studies, clearly demonstrates that exposure to ubiquitous environmental stressors, many of which are carcinogens or suspected carcinogens, are capable of causing alterations in methylation and expression of TEs and initiate retrotransposition events. Evidence summarized in this review suggests that TEs are the sensitive endpoints for detection of effects caused by such environmental stressors, as ionizing radiation (terrestrial, space, and UV-radiation), air pollution (including particulate matter [PM]-derived and gaseous), persistent organic pollutants, and metals. Furthermore, the significance of these effects is characterized by their early appearance, persistence and presence in both, target organs and peripheral blood. Altogether, these findings suggest that TEs may potentially be introduced into safety and risk assessment and serve as biomarkers of exposure to environmental stressors. Furthermore, TEs also show significant potential to become invaluable surrogate biomarkers in clinic and possible targets for therapeutic modalities for disease treatment and prevention.

Effects of heat and UV radiation on the mobilization of transposon mariner-Mos1.

There are many complex interactions between transposable elements (TEs) and host genomes. Environmental changes that induce stressful conditions help to contribute for increasing complexity of these interactions. The transposon mariner-Mos1 increases its mobilization under mild heat stress. It has putative heat shock elements (HSEs), which are probably activated by heat shock factors (HSFs). Ultraviolet radiation (UVC) is a stressor that has been suggested as able to activate heat shock protein genes (Hsp). In this study, we test the hypothesis that if UVC induces Hsp expression, as heat does, it could also promote mariner-Mos1 transposition and mobilization. The Drosophila simulans white-peach is a mutant lineage that indicates the mariner-Mos1 transposition phenotypically through the formation of mosaic eyes. This lineage was exposed to UVC or mild heat stress (28 °C) in order to evaluate the induction of mariner-Mos1 expression by RT-qPCR, as well as the mariner-Mos1 mobilization activity based on the count number of red spots in the eyes. The effects of both treatments on the developmental time of flies and cell cycle progression were also investigated. Both the analysis of eyes and mariner-Mos1 gene expression indicate that UVC radiation has no effect in mariner-Mos1 transposition, although heat increases the expression and mobilization of this TE soon after the treatment. However, the expression of Hsp70 gene increased after 24 h of UVC exposure, suggesting different pathway of activation. These results showed that heat promotes mariner-Mos1 mobilization, although UVC does not induce the expression or mobilization of this TE.

[Peculiar features of forming radiation effects in inbred populations of Drosophila melanogaster differing in cytotype].

A comparative evaluation of the sensitivity of inbred wild-type flies differing in the cytotype to the action of low-intensity radiation of different duration was conducted taking into account the integral parameters of survival. The strong dependence of the frequency of radiation-induced DNA damage (in the neutralpH version) to the cells of individuals on the dose of low-intensity radiation and stages of spermatogenesis was established. The hyper-radiosensitivity was found in the individuals of Charolles (R-cytotype), Harwich (P-cytotype), and Oregon-R (H-cytotype) strains irradiated during the early stages of spermatogenesis (spermatogonia-spermatocytes) and containing in their genotype transposons Bari 1, P and hobo, respectively. While drosophila line Canton-S exhibited dysgenetic properties against the background of several cytotypes (E, I and M), the effect of hormesis was identified under the same experimental conditions. With the increase in the dose of low-intensity irradiation, the frequency of the DNA damage either increased (for Canton-S) or reduced (for Harwich and Charolles). At that, the profile of fertility and. survival of wild-type stocks studied was maintained at a significantly high level. The important role of the cytotype and mobile genetic elements responsible for its formation in the modification of the effects of low-intensity γ-radiation is shown.

[Induction of transpositions of hobo-elements in chronically irradiated cells of dysgenetic and non-dysgenetic individuals of Drosophila melanogaster].

This paper studies the effect of chronic γ-radiation of different intensities on the induction of hobo-elements in cells ofdysgenetic and non-dysgenetic drosophila species. The level of gonadal atrophy, DNA damage, and mutability of the mini-white locus is estimated. It is shown that the frequency of displacements of the hobo-elements increases with the increase in the chronic irradiation dose, where an essential role belongs to the maternal effect. The level of DNA damage in the cells of embryos and larvae varies and depends on the conditions of induction of hobo-transposons. Analysis of the PCR products showed that chronic irradiation in a certain range of accumulated doses is able to induce formation of new copies of the hobo-elements. At the same time, the structure of deleted hobo-sequences may vary in response to higher doses of irradiation.

[Estimation of the levels of radiation-induced P-element transposition in Drosophila melanogaster experimental populations and laboratory strains].

When experimental P + M populations were exposed to chronic gamma-irradiation (0.31 mGy/h), the highest instability level of the singed-weak (sn(w)) locus was observed in F3-F10 with a subsequent decrease and stabilization of the mutation rate. The sn(w) mutation rate was within the range of spontaneous variation in conditions of P-M hybrid dysgenesis and irradiation of males of the Harwich laboratory strain with active P elements at 1.61 mGy/h. The instability of the sn(w) locus was significantly higher at lower dose rates (0.23 and 0.31 mGy/h), suggesting a nonlinear dose-effect relationship.

RNA silencing: Mechanism, biology and responses to environmental stress.

Much early work on environmental stress, including ionizing radiation and environmental toxins, emphasised their action on DNA and subsequent mutagenesis in long term effects including germ cell mutagenesis, carcinogenesis and trans-generational effect. However, recent studies are increasingly pointing a complementary role of epigenetic effects in these processes. While a substantial part of the literature focuses on DNA methylation, there is increasing recognition of the role of non-coding RNAs, including small-, micro-, and pi-RNAs, as well as transposable elements. These play key roles in carcinogenesis, and in germ cell changes including trans-generational effects.

Irradiation-induced Deinococcus radiodurans genome fragmentation triggers transposition of a single resident insertion sequence.

Stress-induced transposition is an attractive notion since it is potentially important in creating diversity to facilitate adaptation of the host to severe environmental conditions. One common major stress is radiation-induced DNA damage. Deinococcus radiodurans has an exceptional ability to withstand the lethal effects of DNA-damaging agents (ionizing radiation, UV light, and desiccation). High radiation levels result in genome fragmentation and reassembly in a process which generates significant amounts of single-stranded DNA. This capacity of D. radiodurans to withstand irradiation raises important questions concerning its response to radiation-induced mutagenic lesions. A recent study analyzed the mutational profile in the thyA gene following irradiation. The majority of thyA mutants resulted from transposition of one particular Insertion Sequence (IS), ISDra2, of the many different ISs in the D. radiodurans genome. ISDra2 is a member of a newly recognised class of ISs, the IS200/IS605 family of insertion sequences.

[The radiationally induced change of level of double-stranded breaks DNA in neuroblasts of larvae and frequency of lethal mutations in sex cells of males Drosophila melanogaster].

The level of damage DNA in neyroblastes of larvae and frequency of recessive sex-linked lethal mutations of males from chronically irradiated populations Drosophila melanogaster, differing on mobile P-elements patterns, was estimated. Received results testify, that exposition in conditions a chronic gamma-radiation (absorbed radiation dose at one generation is compounds 10 mGy) result to increase of significance of parameters and change of sensitivity of cells to following of an acute irradiation in a dose of 3 Gy.

[The dynamics of P-mobile Drosophila melanogaster element activation in controlled terms of protracted irradiation].

Verification of hypothesis about mobile element activation radiosensitivity change in the conditions of the prolonged irradiation was the research goal. The estimation of orientation of these changes depending on the accumulated dose and their characteristic times were conducted. Two Drosophila melanogaster strains (Canton-S and P-lines) for 20 generations were in the controlled terms of chronic irradiation with 3-dose rate (1.2 x 10(-8), 0.6 x 10(-8) and 0.12 x 10(-8) Gy/c). The dynamics of hybrid dysgenese frequency was explored for each generation of F1 descendants from Canton-S and P-lines crossing. The gradual change of dose response of hybrid disgenesis depending on duration of irradiation of ancestors and dose rate was shown. The complex dynamics of hybrid dysgenese frequency depending on irradiation duration of ancestors and dose rate was shown. The cumulative effect of the prolonged irradiation shows up as adaptation at the lowest dose rate and as exhaustion at the highest dose rate. Question comes into discussion about the features of transitional process and including of protective and adaptive reactions hierarchy at the conditions of radiation factor chronic action.

PCR-based detection of Pol III-transcribed transposons and its application to the rodent model of ultraviolet response.

Cellular levels of RNAs containing transposable elements increase in response to various stresses. Polymerase III (Pol III)-dependent transcripts of transposons are different from transposon-containing RNAs generated by read-through Pol II-dependent transcription. Until now, Pol III transcripts were detected by primer extension followed by time-consuming gel electrophoresis. In this paper, we describe a more sensitive PCR-based method for the selective detection of Pol III-transcribed RNAs. The method is based on the difference in sequences at the 5' ends of the Pol II- and Pol III-dependent transcripts. We employed this method to quantify Pol III transcripts of transposon B1 in rodent cells and revealed that their levels are affected by UV irradiation. We therefore conclude that the abundance of the Pol III-transcribed fraction of cellular RNA may serve as marker of stress response and can be conveniently quantified by the method described.

[The effect of gamma-radiation on induction of the hobo element transposition in Drosophila melanogaster].

The transposition frequency of the hobo mobile element in four successive generations of Drosophila melanogaster strain y2-717 after an acute gamma-irradiation with a dose of 30 Gr amounted to 7.5 x 10(-4) per site per genome per generation. Under the same conditions, PCR analysis of the genomic DNA of y2-717 flies detected new variants of defective hobo sequence. No changes in the hobo localization and PCR products compared with the control were detected in the case of single irradiation with doses of 3 and 30 Gr. The localizations of hobo element on polytene chromosomes of y2-717 strain did not change during 11 generations after five exposures of flies to 30 Gr. Irradiation of a highly unstable D. melanogaster strain y+743 did not increase the number of families with mutant progeny, yet increased the total number of mutant descendants almost twofold, from 5 to 9%.

Pre-exposure to UV irradiation increases the transfer frequency of the IncJ conjugative transposon-like elements R391, R392, R705, R706, R997 and pMERPH and is recA+ dependent.

The enteric conjugative transposon-like IncJ elements R391, R392, R705, R706 and pMERPH, all demonstrated increased conjugative transfer upon UV irradiation. The transfer frequency increased on average from its basal rate of 10(-5) to 10(-3) per recipient, upon pre-exposure to UV irradiation. However, the transfer frequency of R997, which was higher than the other IncJ elements at 10(-3) per donor, showed a smaller increase. This effect was shown to be recA+ dependent in all cases. Using PCR primers directed outwards from the ends of the integrated R391 element it was observed that a circular intermediate of the element forms within the host, which has been proposed to be a transfer intermediate. Using real-time PCR, it was determined that the amount of the circular intermediate produced increased substantially upon UV irradiation.

[Induction of the Tn10 precise excision in E. coli cells after accelerated heavy ions irradiation]. / Induktsiia tochnoi ékspozitsii transpozona Tn10 v kletkakh E. coli pri obluchenii uskorennymi ionami s raznoi lineinoi peredachei énergii.

The influence of the irradiation of different kinds on the induction of the structural mutations in the bacteria Escherichia coli is considered. The regularities of the Tn10 precise excision after accelerated 4He and 12C ions irradiations with different linear energy transfer (LET) were investigated. Dose dependences of the survival and relative frequency of the Tn10 precise excision were obtained. It was shown, that the relative frequency of the Tn10 precise excision is the exponential function from the irradiation dose. Relative biological efficiency (RBE), and relative genetic efficiency (RGE) were calculated, and were treated as the function of the LET.

Various effects on transposition activity and survival of Escherichia coli cells due to different ELF-MF signals.

Previous assays with weak sinusoidal magnetic fields (SMF) have shown that bacteria that had been exposed to a 50 Hz magnetic field (0.1-1 mT) gave colonies with significantly lower transposition activity as compared to sham-exposed bacteria. These experiments have now been extended by using a pulsed-square wave magnetic field (PMF) and, unexpectedly, it was found that bacteria exposed to PMF showed a higher transposition activity compared to the controls. The increase of the transposition activity was positively correlated with the intensity of the magnetic fields (linear dose-effect relation). This phenomenon was not affected by any bacterial cell proliferation, since no significant difference was observed in number and size of PMF-exposed and sham-exposed colonies. In addition, the cell viability of E. coli was significantly higher than that of the controls when exposed to SMF, and lower than that of the controls when exposed to PMF. Under our experimental conditions it was shown that exposure to PMF stimulates the transposition activity and reduces cell viability of bacteria, whereas exposure to SMF reduces the transposition mobility and enhances cell viability. These results suggest that the biological effects of magnetic fields may critically depend on the physical characteristics of the magnetic signal, in particular the wave shape.

Extremely low frequency magnetic fields affect transposition activity in Escherichia coli.

The aim of this study was to verify whether extremely low frequency (ELF) magnetic fields (MF) could affect transposition activity like some environmental stress factors such as heat shock or UV irradiation. Using an Escherichia coli Lac Z(-) strain transformed with a plasmid containing a Tn 10 derivative element expressing beta-galactosidase only after transposition, it was possible to determine the events of transposition evaluating the rate at which the colonies developed dark coloured papillae (Lac Z(+)). We found that those bacteria that had been exposed for a long time (58 h) to a 50 Hz low intensity MF (0.1-1 mT) gave colonies with significantly lower transposition activity compared to sham-exposed bacteria. Such reduction in transposition activity was positively correlated to the intensity of the MF, in a dose-effect manner. This phenomenon was not affected by bacterial cell proliferation, since no significant differences were observed in number, diameter and perimeter between sham-exposed and MF-exposed colonies.

[Prolongation of MGE 412 transposition induction after gamma-irradiation in an isogenic line of Drosophila melanogaster]]. / Prolongatsiia induktsii transpozitsii MGE 412 posle gamma-oblucheniia v izogennoi linii Drosophila melanogaster.

The dose dependence of the rate of gamma-induced transpositions and consequent dynamics of the MGE 412 pattern after gamma-irradiation were investigated in isogenic line 49 in generations F1, F12, F140, and F170. It was shown that the results on dose dependence of transpositions was very similar with the corresponding results of the classic works by Timofeeff-Ressovsky et al. (1935). It is suggested that the transcribed copies of retrotransposon 412 "cure" gamma-radiation-induced double-strand DNA breaks. The phenomenon of prolongation of MGE transposition induction during early generations after treatment was shown. In this period (F1-F12), the maximum transposition rate (lambda approximately equal to 2 x 10(-2) events per MGE copy, per haploid genome, per generation) and the maximum number of heterozygous MGE copies were achieved. In the late generations (F140 and F170), the reduced induction level (lambda approximately 10(-3) was established. In the population of effective size Ne = 2000 individuals, this corresponds to the state when lambda >> 1/4Ne, i.e., when the transposition flow prevails over the MGE copy loss by genetic drift. These data together with some indirect evidence argue for the hypothesis that the spontaneous transposition rate is proportional to the average number of heterozygous MGE copies per diploid genome.

Magnetic field exposure stimulates transposition through the induction of DnaK/J synthesis.

Like some naturally occurring environmental stress factors such as heat shock and UV irradiation, magnetic field exposure is also stimulatory to transposition activity. This feature could be illustrated by a bacterial conjugation study using an Escherichia coli strain that carries the transposable element Tn5 as the donor. When the donor cultures were exposed to a low-frequency (50 Hz) magnetic field of 1.2 mT, Tn5 located on the bacterial chromosome was stimulated to transpose and settled on the extrachromosomal episome, and eventually transferred to the recipient cell through conjugation. Such transposition activity stimulation was mediated by the induced synthesis and accumulation of the heat shock proteins DnaK/J.