Drosophila p53 preserves genomic stability by regulating cell death

When animal cells are exposed to stressful conditions, the tumor suppressor protein p53 restrains growth by promoting an arrested cell cycle or initiating a cell death program. How these distinct fates are specified through the action of a single protein is not known. To study its functions in vivo we produced a targeted mutation at the Drosophila p53 (Dmp53) locus. We show that Dmp53 is required for damage-induced apoptosis but not for cell-cycle arrest. Dmp53 function is also required for damage-induced transcription of two tightly linked cell death activators, reaper and sickle. When challenged by ionizing radiation, Dmp53 mutants exhibit radiosensitivity and genomic instability. Hence, elevated mutant loads were not caused by defective checkpoint functions but instead correlated with failures in p53-associated cell death. Our studies support the notion that core ancestral functions of the p53 gene family are intimately coupled to cell death as an adaptive response to maintain genomic stability.

Distinct pathways mediate UV-induced apoptosis in Drosophila embryos

Cell death in Drosophila is regulated by many of the same signals that control apoptosis in mammalian systems. For all the three major cell death pathways that have been described in humans, homologous components have been identified in Drosophila. Here we report that distinct pathways mediate UV-induced apoptosis at different developmental stages in the Drosophila embryo. In midstage embryos, UVC irradiation induces reaper expression and cell death through a mei-41(dATM)-dependent pathway; UVB does not have the same effect. In contrast, in pregastrulation embryos, both UVB and UVC promote apoptosis via transcriptional induction of the Drosophila Apaf-1/ced-4 homolog. This early UV response requires E2F but not mei-41 function and appears to be independent of DNA damage.

[Adaptation processes in natural Drosophila populations in radiation contaminated Belarus regions before and after radiation exposure removal]

We have shown that natural drosophila populations from the settlement Vetka of Gomel region with increased radiation background are more adapted to mutagenic effect of radiation than drosophila populations from Berezinsky reserve (the control). After the populations were placed into laboratory thermostat adaptation of Vetka population remained within 6-8 generations without irradiation. However the control population became more resistant too. So, the keeping of natural drosophila populations under laboratory conditions was a stress and led to unspecific adaptation the same as a low level of radiocontamination did. These facts should be considered in studying dynamics of the mutation level during radionuclide removal in animals caught in radiocontaminated regions and placed in vivaria conditions.

[The role of reaper-dependent apoptosis in radiation-induced life-span alterations in Drosophila melanogaster]

This is the result of studying on a problem of radio-induced ageing. From the point of view of radiation genetics it is perspective to investigate influence of low doze irradiation on individuals with the mutant phenotypes that allows to assume a role of separate genes and mechanisms controllable by them in determination of life span and ageing. The role of a reaper-dependent way of apoptosis regulation in the induced change of life span is shown. The assumption is put forward that apoptosis has the important role during ageing an animal organism.

Circadian light input in plants, flies and mammals

The rotation of our planet results in daily changes in light and darkness, as well as seasons with characteristic photoperiods. Adaptation to these daily and seasonal changes in light properties (and associated changes in the environment) is important to the sustained survival of higher life forms on our planet. Many organisms use their intrinsic circadian oscillator or clock to orchestrate daily rhythms in behaviour and physiology to adapt to diurnal changes. Some higher organisms use the same oscillator to monitor day length in selecting the appropriate season for reproductive behaviour. Organisms have developed irradiance measurement mechanisms to ignore photic noise (lightning, moonlight), and use the light of dusk and dawn for circadian photoentrainment. They have also devised multiple photoreceptors and signalling cascades to buffer against changes in the spectral composition of natural light. The interaction of the clock with ambient light is, therefore, quite intricate.

[Characteristic features of induced mutagenesis in hybrid dysgenesis systems of Drosophila melanogaster]

The mutagenic effect of low-dose gamma-irradiation was studied in Drosophila melanogaster systems of hybrid dysgenesis by estimating polytene chromosome rearrangements, recombination frequency, and viability at the embryonic and postembryonic developmental stages. A dose of gamma-irradiation which had no effect detectable by routine line crossing proved to significantly reduce the number of recombinants in the H-E and P-M systems and mortality at postembryonic stages. However, this combined effect was obtained if irradiation followed transposition, i.e., it depended on the application sequence of the mutagenic factors. The reverse order of the mutagenic treatment led to summation of the effects: as compared to either control, the frequencies of the dominant allele mutations as well as the larval and pupal mortality in F2 increased significantly (at the level of 99.9%). This allowed us to estimate the contribution of extremely low-dose gamma-irradiation into the mutagenic effect, which was impossible under routine conditions.

Chk2 regulates irradiation-induced, p53-mediated apoptosis in Drosophila

The tumor suppressor function of p53 has been attributed to its ability to regulate apoptosis and the cell cycle. In mammals, DNA damage, aberrant growth signals, chemotherapeutic agents, and UV irradiation activate p53, a process that is regulated by several posttranslational modifications. In Drosophila melanogaster, however, the regulation modes of p53 are still unknown. Overexpression of D. melanogaster p53 (Dmp53) in the eye induced apoptosis, resulting in a small eye phenotype. This phenotype was markedly enhanced by coexpression with D. melanogaster Chk2 (DmChk2) and was almost fully rescued by coexpression with a dominant-negative (DN), kinase-dead form of DmChk2. DN DmChk2 also inhibited Dmp53-mediated apoptosis in response to DNA damage, whereas overexpression of Grapes (Grp), the Drosophila Chk1-homolog, and its DN mutant had no effect on Dmp53-induced phenotypes. DmChk2 also activated the Dmp53 transactivation activity in cultured cells. Mutagenesis of Dmp53 amino terminal Ser residues revealed that Ser-4 is critical for its responsiveness toward DmChk2. DmChk2 activates the apoptotic activity of Dmp53 and Ser-4 is required for this effect. Contrary to results in mammals, Grapes, the Drosophila Chk1-homolog, is not involved in regulating Dmp53. Chk2 may be the ancestral regulator of p53 function.

Genetic effects of balloon flight in Drosophila melanogaster

Drosophila males were flown in balloons and crossed, after recovery, in order to investigate possible genetic effects of cosmic rays. No significant effect was observed in the lethal and dominant mutation rate.

Influence of the period-dependent circadian clock on diurnal, circadian, and aperiodic gene expression in Drosophila melanogaster

We measured daily gene expression in heads of control and period mutant Drosophila by using oligonucleotide microarrays. In control flies, 72 genes showed diurnal rhythms in light-dark cycles; 22 of these also oscillated in free-running conditions. The period gene significantly influenced the expression levels of over 600 nonoscillating transcripts. Expression levels of several hundred genes also differed significantly between control flies kept in light-dark versus constant darkness but differed minimally between per(01) flies kept in the same two conditions. Thus, the period-dependent circadian clock regulates only a limited set of rhythmically expressed transcripts. Unexpectedly, period regulates basal and light-regulated gene expression to a very broad extent.

Results of biological experiments carried out under conditions of "Vostok" flights with the participation of cosmonauts A.G. Nikolajev, P.R. Popovich and V.F. Bykovsky

The data are presented on a study of the effect of space flight factors, particularly of weightlessness and radiation, on the fertilization, growth and development of Drosophila melanogaster and on the mechanism of heredity in Tradescantia paludosa. Copulation, oviposition and development of Drosophila are shown to be possible under 4-day weightless conditions. A distortion in the sex ratio has been registered in the cultures of flies grown in flight. Three types of changes in Tradescantia microspores brought about by flight factors have been revealed, i.e. chromosome rearrangements, distortions in the mitotic mechanism and stimulation of growth processes in the cell. It is suggested that rearrangements of chromosomes are caused by the action of vibrations and accelerations while distortions in the mechanism of mitosis are mainly related to the weightlessness effect.

Satellite biological experiments--major results and problems

The data on the results of biological experiments carried out on Vostok 5 and Vostok 6 are presented. Space flight factors are shown to cause in hereditary structures of some biological objects (seeds of higher plants, lysogenic bacteria, Tradescantia microspores, etc.) distortions of a small but statistically significant value. Changes in physiological functions of certain objects (seeds of higher plants, etc.) have been also detected. These data are in good agreement with the results of flight experiments carried out in 1960-1962. Prospects of research of the biological effect of cosmic radiation and weightlessness are considered with respect to flight experiments.

Light wavelength dependency of mating activity in the Drosophila melanogaster species subgroup

The action spectra of mating activity among the six species of the Drosophila melanogaster species subgroup were compared to understand how light wavelength affects mating activity. The species fell into three groups with respect to the action spectrum of mating activity. We chose one representative species from each of the three types for detailed study: D. melanogaster, D. sechellia and D. yakuba. The mating activities were investigated under three different light intensities of three monochromatic lights stimulus. Each species showed a unique spectral and intensity response. To know the evolutionary meaning of the light wavelength dependency of mating activity, we superimposed the type of action spectrum of mating activity in these six species on a cladogram. Mating inhibition under UV was conserved in evolution among these species. Furthermore we clarified that D. melanogaster showed low mating activity under UV because males courted less under UV.

Variations in the recombination rate of Drosophila melanogaster induced by balloon flight

Drosophila males, heterozygous for b, pr, cn and en genes, were submitted to balloon flights, ceiling time ranging from about 8 hours (flights performed in France) to 22 hours (transmediterranean flight). Effects on recombination were investigated on progeny after breeding with females homozygous for the same genes. The transmediterranean flight and one flight performed in France resulted in a significantly higher recombination rate.

Molecular characterization and developmental expression of the TFIIH factor p62 gene from Drosophila melanogaster: effects on the UV light sensitivity of a p62 mutant fly

TFIIH is a multiprotein complex that has a central role in the RNA pol II mediated transcription, in DNA repair and in the control of the cell cycle. Mutations in some components of TFIIH are associated with three hereditary human syndromes: xeroderma pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD). The p62 protein is a structural component of the TFIIH core and no syndromes have been identified up to date by mutations in this human gene. In this work we report the molecular and genetic characterization of the Drosophila melanogaster p62 gene (Dmp62). The Dmp62 gene product shows high identity with its human and mouse homologues. Using computer analysis we identified several common motifs in the p62 proteins from different organisms, suggesting that these motifs could be involved in possible protein-protein interactions within the TFIIH complex or with other transcription and DNA repair factors. The Dmp62 transcript is expressed at similar levels throughout development, although there is a significant increase of the transcript level during the late embryogenesis and in the adult male. The analysis of a Drosophila line with a P-element enhancer trap insertion at the Dmp62 5'-UTR that directs the lac-Z expression from the Dmp62 promoter, showed a high level of expression in the gut, the testis and the pericardial cells. A P-element that disrupts the Dmp62 gene (Dmp62mut) produces early embryo lethality in homozygous flies. Heterozygous Dmp62mut larvae are more sensitive to UV light irradiation, and those individuals that are able to develop into adults have severe abdominal cuticular damage after UV light irradiation.

[Effect of low intensity pulsed laser radiation of basic parameters of aging in Drosophila melanogaster]

The effect of the low-intensive impulse laser radiation (LILR) on the life span of Drosophila melanogaster has been studied. The flies at various stages of their life (larvae and imago) were exposed to LILR. The estimation of the effect of LILR was carried out on the basis of the analysis of the basis parameters of aging. We found out increasing as well as shortening effects of the life span. The direction of the effect depends on parameters of radiation, stage of development of irradiated individuals and their sex.

Biosatellite II--physiological and somatic effects on insects

Interesting physiological and somatic effects of space flight have been observed in a variety of insects on board Biosatellite II. Wasps, beetles and fruit flies have demonstrated positive effects of the space flight alone or in combination with irradiation. In the flour beetle, Tribolium confusum, the incidence of a developmental wing abnormality was measured. This abnormality, which mimics the mutation known as "split", was significantly increased in beetles which were flown as young pupae, pre-irradiated with X rays to bring them into their sensitive dose range and gamma irradiated during flight. Wing abnormalities increased from a ground value of 29.9 per cent to a value of 44.8 per cent. The length of the pupal period was also measured. Although there was a significant increase of the flight pupal period over that of the ground control, the most likely explanation seems to be the temperature drop of the flight samples between separation and retrieval of the flight capsule. In the parasitic wasp, Habrobracon juglandis, flown in the adult stage, several interesting results have been obtained in terms of reproductive performance, life span and enzyme activity. Reproductive performance, measured by the average number of eggs laid/female/day, was unaffected by flight for control unirradiated wasps. However, for females X rayed with 2000 R prior to flight, the characteristic depression of egg-laying at 10 days post-irradiation was negligible in the flight animals. A more pronounced effect was observed in those females which received the chronic 2667 R gamma ray dose in flight; egg production actually progressively increased to twice the level of the ground sample. It was observed that males were disoriented in their mating behavior for 2 days after the flight. When the dose level data was pooled, the life span of females was found to be significantly longer in the flight group. Upon analysis of the activity of the enzyme, xanthine dehydrogenase (XDH), adult flight males were found to have a significantly decreased XDH activity compared with ground controls. No significant difference was found between female F1 progeny of flight and ground males. XDH activity was also analyzed in F1 progeny of Drosophila melanogaster, orbited as adults and larvae. For the F1 male progeny of adult males, there was a significantly depressed average XDH activity compared with ground controls for the highest irradiation dose. For F1 male progeny of flight larvae, there was a statistically decrease of XDH activity only between the off-spring of irradiated flight and ground larvae. Further somatic changes were observed in Drosophila larvae, in which chromosome aberrations were studied.

[Study on genetic radioresistance of natural Drosophila Melanogaster population from radionuclide contaminated regions of Byelarus]

Over the period from 1998 to 2000 adaptation to unfavorable ecological factors was revealed to be formed in natural Drosophila melanogaster populations from various regions of Belarus with increased radiation background due to the Chernobyl accident. This adaptation was shown to be of non-specific character, since the populations from radiation regions were more resistant to the effect of not only factors of physical nature (irradiation), but also to that of chemical mutagen ethylmethanesulphonate. Assessment of population resistance was carried out by means of tests of dominant lethal mutations and recessive sex-linked lethal mutations.

Genetic effects induced by neutrons in Drosophila melanogaster I. Determination of absorbed dose

A method to obtain the absorbed dose in Drosophila melanogaster irradiated in the thermal column facility of the Triga Mark III Reactor has been developed. The method is based on the measurements of neutron activation of gold foils produced by neutron capture to obtain the neutron fluxes. These fluxes, combined with the calculations of kinetic energy released per unit mass, enables one to obtain the absorbed doses in Drosophila melanogaster.

[Role of apoptotic cell death in radioinduced aging in Drosophila melanogaster]

The attempt in made to estimate a role of programmed cell death (apoptosis) in radio-induced life span alteration and aging. It was shown with the use of mutant Drosophila melanogaster laboratory strains, that the disfunction of a reaper-dependent apoptosis pathway, together with the action of ionizing radiation and/or apoptosis inductor etoposide, could lead to change of life span and a pace of aging. In Drosophila strain with defect of proapoptosis gene reaper, the increase of life span after irradiation and etoposide treatment was observed. At the same time the strain with overexpression of a protease dcp-1 gene and the strain with the defect of antiapoptosis diap-1/th gene decreased the life span after irradiation and etoposide treatment. The obtained facts are discussed from a position of participation of apoptosis deregulation in radio-induced and natural aging of whole organisms.

Mechanism of the fluorescent light induced suppression of Curly phenotype in Drosophila melanogaster

A dominant mutation Curly (Cy), frequently used as a marker on the second chromosome in Drosophila melanogaster, was previously shown to be suppressed by several factors, including larval crowding, low temperature, and fluorescent light. While the first two factors affect this mutation only partially, fluorescent tube exposed flies exhibit an almost completely suppressed (wild type) phenotype. This suppressive effect is the result of a combination of the electric field and light, both factors being produced by common fluorescent tubes. In this study, experiments were carried out to clarify the basic mechanism of this unique phenomenon. Two fluorescent tube sensitive stages of Drosophila development were found in the second half of embryonic development and first half of the pupal stage. Riboflavin, which is administered to Drosophila larvae with yeast, and decomposed by light, seems to play a key role in this phenomenon. In a medium lacking riboflavin caused by light exposure, Cy expression is inhibited by the action of electric field. Positive results of experiments with lithium ions, which block the opening of Ca(2+) channels, support the hypothesis that electromagnetic fields may alter ion currents during ontogenic development of Drosophila, and thus influence, expression of the Cy gene. Also, fluorescent light induces an overexpression of a specific protein in the imaginal wing disc of Cy pupae.

[Radioinduced change in life span of laboratory strains of Drosophila melanogaster]

Chronic irradiation (accumulated dose 0.6-0.8 Gy) was shown to change the life span in male Drosophila melanogaster. Death was retarded in wild-type strains and accelerated in mutant strains defective in DNA repair and displaying a higher sensitivity to induction of apoptosis.

[Drosophila gene rad201 controls cell cycle arrest in irradiated cells]

Mitotic activity of larval neuroblasts was studied in the wild-type Oregon R and mutant rad201G1 and mei-41D5 Drosophila melanogaster at different intervals after gamma-irradiation at a dose of 6 Gy. The data obtained suggest that the rad201 gene is involved in the control of the cell cycle.

[Relative genetic effectiveness of fission neutrons in inducing various types of recessive mutation in 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.

Increased UV light sensitivity in transgenic Drosophila expressing the antisense XPD homolog

The XPD gene is required for excision repair of UV-damaged DNA and is an important component of nucleotide excision repair (NER). Mutations in the XPD gene generate the cancer-prone syndrome xeroderma pigmentosum, Cockayne's syndrome, and trichothiodystrophy. XPD is a component of the TFIIH transcription factor, which is essential for RNA polymerase II elongation. In this work, we report the construction of transgenic flies overexpressing the antisense RNA of the Drosophila melanogaster XPD homolog (DmXPD). These flies show an increased sensitivity to UV radiation compared with the wild-type. This is an expected phenotype if the XPD function is affected and indicates that the antisense approach may be an alternative in the study of TFIIH functions in Drosophila.

[Prolongation of MGE 412 transposition induction after gamma-irradiation in an isogenic line of 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.