Identification of a DNA polymerase beta-like form in Drosophila melanogaster adult flies.

DNA polymerase beta is widely distributed in the eukariotes. So far, few examples are known in which a DNA polymerase alpha -like form alone is reported. Surprisingly, DNA polymerase beta was not detected in Drosophila embryos, while it is present in the cells of multicellular species from sponge to mammals. In view of the relevance of Drosophila as a model biological system for studying the role of the various DNA metabolism enzymes in vivo we have reinvestigated the presence of the DNA polymerase beta-like form in Drosophila adult flies.Here we report the occurrence in Drosophila melanogaster adult flies of a DNA polymerase activity that, for its NEM(1) resistance, template specificity, sensitivity to ddTTP, sedimentation coefficient and nuclear localization can be classified as a beta-like form.     

Expression of bovine superoxide dismutase in Drosophila melanogaster augments resistance of oxidative stress.

Superoxide dismutases (SOD) play a major role in the intracellular defense against oxygen radical damage to aerobic cells. In eucaryotes, the cytoplasmic form of the enzyme is a 32-kDa dimer containing two copper and two zinc atoms (CuZn SOD) that catalyzes the dismutation of the superoxide anion (O2-) to H2O2 and O2. Superoxide-mediated damage has been implicated in a number of biological processes, including aging and cancer; however, it is not certain whether endogenously elevated levels of SOD will reduce the pathological events resulting from such damage. To understand the in vivo relationship between an efficient dismutation of O2- and oxidative injury to biological structures, we generated transgenic strains of Drosophila melanogaster overproducing CuZn SOD. This was achieved by microinjecting Drosophila embryos with P-elements containing bovine CuZn SOD cDNA under the control of the Drosophila actin 5c gene promoter. Adult flies of the resulting transformed lines which expressed both mammalian and Drosophila CuZn SOD were then used as a novel model for evaluating the role of oxygen radicals in aging. Our data show that expression of enzymatically active bovine SOD in Drosophila flies confers resistance to paraquat, an O2(-)-generating compound. This is consistent with data on adult mortality, because there was a slight but significant increase in the mean lifespan of several of the transgenic lines. The highest level of expression of the active enzyme in adults was 1.60 times the normal value. Higher levels may have led to the formation of toxic levels of H2O2 during development, since flies that died during the process of eclosion showed an unusual accumulation of lipofuscin (age pigment) in some of their cells. In conclusion, our data show that free-radical detoxification has a minor by positive effect on mean longevity for several strains.     

The Drosophila genome

The past year has been a spectacular one for Drosophila research. The sequencing and annotation of the Drosophila melanogaster genome has allowed a comprehensive analysis of the first three eukaryotes to be sequenced-yeast, worm and fly-including an analysis of the fly's influences as a model for the study of human disease. This year has also seen the initiation of a full-length cDNA sequencing project and the first analysis of Drosophila development using high-density DNA microarrays containing several thousand Drosophila genes. For the first time homologous recombination has been demonstrated in flies and targeted gene disruptions may not be far off.     

Functional analysis of Drosophila melanogaster BRCA2 in DNA repair

The human BRCA2 cancer susceptibility protein functions in double-strand DNA break repair by homologous recombination and this pathway is conserved in the fly Drosophila melanogaster. Although a potential Drosophila melanogaster BRCA2 orthologue (dmbrca2; CG30169) has been identified by sequence similarity, no functional data addressing the role of this protein in DNA repair is available. Here, we demonstrate that depletion of dmbrca2 from Drosophila cells induces sensitivity to DNA damage induced by irradiation or treatment with hydroxyurea. Dmbrca2 physically interacts with dmrad51 (spnA) and the two proteins become recruited to nuclear foci after DNA damage. A functional assay for DNA repair demonstrated that in flies dmbrca2 plays a role in double-strand break repair by gene conversion. Finally, we show that depletion of dmbrca2 in cells is synthetically lethal with deficiency in other DNA repair proteins including dmparp. The conservation of the function of BRCA2 in Drosophila will allow the analysis of this key DNA repair protein in a genetically tractable organism potentially illuminating mechanisms of carcinogenesis and aiding the development of therapeutic agents.     

Modeling human neurodegenerative diseases in Drosophila: on a wing and a prayer

The ability of Drosophila genetics to reveal new insights into human neurodegenerative disease is highlighted not only by mutants in flies that show neuronal cell loss, but also by targeted expression of human disease genes in the fly. Moreover, study of Drosophila homologs of various human disease genes provides new insight into fundamental aspects of protein function. These recent findings confirm the remarkable homology of gene function in flies when compared with humans. With the advent of complete genomic sequencing on the horizon, Drosophila will continue to be an outstanding model system in which to unravel the complexities, causes and treatments for human neural degeneration.     

ATM is required for telomere maintenance and chromosome stability during Drosophila development

ATM is a large, multifunctional protein kinase that regulates responses required for surviving DNA damage: including DNA repair, apoptosis, and cell cycle checkpoints. Here, we show that Drosophila ATM function is essential for normal adult development. Extensive, inappropriate apoptosis occurs in proliferating atm mutant tissues, and in clonally derived atm mutant embryos, frequent mitotic defects were seen. At a cellular level, spontaneous telomere fusions and other chromosomal abnormalities are common in atm larval neuroblasts, suggesting a conserved and essential role for dATM in the maintenance of normal telomeres and chromosome stability. Evidence from other systems supports the idea that DNA double-strand break (DSB) repair functions of ATM kinases promote telomere maintenance by inhibition of illegitimate recombination or fusion events between the legitimate ends of chromosomes and spontaneous DSBs. Drosophila will be an excellent model system for investigating how these ATM-dependent chromosome structural maintenance functions are deployed during development. Because neurons appear to be particularly sensitive to loss of ATM in both flies and humans, this system should be particularly useful for identifying cell-specific factors that influence sensitivity to loss of dATM and are relevant for understanding the human disease, ataxia-telangiectasia.     

Effects of reduced natural background radiation on Drosophila melanogaster growth and development as revealed by the FLYINGLOW program

Natural background radiation of Earth and cosmic rays played a relevant role during the evolution of living organisms. However, how chronic low doses of radiation can affect biological processes is still unclear. Previous data have indicated that cells grown at the Gran Sasso Underground Laboratory (LNGS, L'Aquila) of National Institute of Nuclear Physics (INFN) of Italy, where the dose rate of cosmic rays and neutrons is significantly reduced with respect to the external environment, elicited an impaired response against endogenous damage as compared to cells grown outside LNGS. This suggests that environmental radiation contributes to the development of defense mechanisms at cellular level. To further understand how environmental radiation affects metabolism of living organisms, we have recently launched the FLYINGLOW program that aims at exploiting Drosophila melanogaster as a model for evaluating the effects of low doses/dose rates of radiation at the organismal level. Here, we will present a comparative data set on lifespan, motility and fertility from different Drosophila strains grown in parallel at LNGS and in a reference laboratory at the University of L'Aquila. Our data suggest the reduced radiation environment can influence Drosophila development and, depending on the genetic background, may affect viability for several generations even when flies are moved back to normal background radiation. As flies are considered a valuable model for human biology, our results might shed some light on understanding the effect of low dose radiation also in humans.     

Modeling human mitochondrial diseases in flies

Human mitochondrial diseases are associated with a wide range of clinical symptoms, and those that result from mutations in mitochondrial DNA affect at least 1 in 8500 individuals. The development of animal models that reproduce the variety of symptoms associated with this group of complex human disorders is a major focus of current research. Drosophila represents an attractive model, in large part because of its short life cycle, the availability of a number of powerful techniques to alter gene structure and regulation, and the presence of orthologs of many human disease genes. We describe here Drosophila models of mitochondrial DNA depletion, deafness, encephalopathy, Freidreich's ataxia, and diseases due to mitochondrial DNA mutations. We also describe several genetic approaches for gene manipulation in flies, including the recently developed method of targeted mutagenesis by recombinational knock-in.     

Automated analysis of courtship suppression learning and memory in Drosophila melanogaster

Study of the fruit fly, Drosophila melanogaster, has yielded important insights into the underlying molecular mechanisms of learning and memory. Courtship conditioning is a well-established behavioral assay used to study Drosophila learning and memory. Here, we describe the development of software to analyze courtship suppression assay data that correctly identifies normal or abnormal learning and memory traits of individual flies. Development of this automated analysis software will significantly enhance our ability to use this assay in large-scale genetic screens and disease modeling. The software increases the consistency, objectivity, and types of data generated.     

Drosophila homologs of FANCD2 and FANCL function in DNA repair

Fanconi anemia (FA) is a genetically heterogeneous disease characterized by developmental defects, progressive bone marrow failure and cancer susceptibility. Cells derived from patients with FA show spontaneous chromosomal aberrations and hypersensitivity to cross-linking agents, indicating a cellular defect in DNA repair. Among the 12 FA genes, only FANCD2, FANCL and FANCM have Drosophila homologs. Given this difference between the human and Drosophila FA pathways, it is unknown whether the fly homologs function in DNA repair. Here, we report that knockdown of Drosophila FANCD2 or FANCL leads to specific hypersensitivity to cross-linking agents. Further analysis revealed that FANCD2 and FANCL function in a linear pathway with FANCL being necessary for the monoubiquitination of FANCD2. FANCD2 mutants also exhibited the same defect in the ionizing radiation-inducible S-phase checkpoint that is seen in mammalian cells deficient for this gene. Finally, in an assay for inactivating mutations, FANCD2 mutants have an elevated mutation rate in response to nitrogen mustard, indicating that these flies are hypermutable. Taken together, these data demonstrate that Drosophila FANCD2 and FANCL play a critical role in DNA repair. Because of the lack of other FA genes, further studies will determine whether the conserved FA genes function as the minimal machinery or whether additional genes are involved in the Drosophila FA pathway.     

Circadian timekeeping in Drosophila melanogaster and Mus musculus

The discovery of the period gene mutants in 1971 provided the first evidence that daily rhythms in the sleep-wake cycle of a multicellular organism, the fruit fly Drosophila melanogaster, had an underlying genetic basis. Subsequent research has established that the biological clock mechanism in flies and mammals is strikingly similar and functions as a bimodal switch, simultaneously turning on one set of genes and turning off another set and then reversing the process every 12 h. In this chapter, the current model of the clock mechanism in Drosophila will be presented. This relatively basic model will then be used to outline the general rules that govern how the biological clock operates in mammals.     

The effects of age on radiation resistance and oxidative stress in adult Drosophila melanogaster

Drosophila melanogaster (fruit fly) is a well-established model organism for genetic studies of development and aging. We examined the effects of lethal ionizing radiation on male and female adult Drosophila of different ages, using doses of radiation from 200 to 1500 Gy. Fifty percent lethality 2 days postirradiation (LD(50/2)) in wild-type 1-day-old adult fruit flies was approximately 1238 Gy for males and 1339 Gy for females. We observed a significant age-dependent decline in the radiation resistance of both males and females. Radiation damage is postulated to occur by the generation of oxygen radicals. An age-related decline in the ability of flies to resist an agent that induces oxygen radicals, paraquat, was observed when comparing 10- and 20-day adults. Female flies are more resistant to paraquat than male flies. Oxidative stress mediated by paraquat was additive with sublethal exposures to radiation in young adults. Therefore, the ability to repair the damage caused by oxygen radicals seems to decline with the age of the flies. Because Drosophila adults are largely post-mitotic, our data suggest that adult Drosophila melanogaster can serve as an excellent model to study the factors responsible for radiation resistance in post-mitotic tissue and age-dependent changes in this resistance.     

Fruits and flies: a genomics perspective of an invertebrate model organism.

The increasing number of species for which a full genome sequence is available offers rich pickings for geneticists, but comparative analysis and assembly of information gathered across species does not always lead to answers about the function of a particular gene. This paper aims to place the invertebrate model system--the fly Drosophila melanogaster--into this playing field and to discuss how the organism arrived at its position in functional genetic analysis. Indeed, despite the wealth of knowledge on how a fly lives, breathes and flies, this organism is likely to remain a player in the analysis of biological, disease and pharmaceutical processes. The fast genetics Drosophila offers, combined with a well-annotated genome and a wealth of techniques facilitating gene function discovery, will ensure its place in functional genomics for some time to come. Although the fly cannot speak, it certainly can tell a tale.     

Research resources for Drosophila: the expanding universe

Drosophila melanogaster has been the subject of research into central questions about biological mechanisms for almost a century. The experimental tools and resources that are available or under development for D. melanogaster and its related species, particularly those for genomic analysis, are truly outstanding. Here we review three types of resource that have been developed for D. melanogaster research: databases and other sources of information, biological materials and experimental services. These resources are there to be exploited and we hope that this guide will encourage new uses for D. melanogaster information, materials and services, both by those new to flies and by experienced D. melanogaster researchers.     

Conservation of the expression of Dll, en, and wg in the eye-antennal imaginal disc of stalk-eyed flies

SUMMARY We studied the developmental basis of exaggerated eye span in two species of stalk-eyed flies ( Cyrtodiopsis dalmanni and Sphyracephala beccarri ). These flies have eyes laterally displaced at the end of eyestalks, and males have greatly exaggerated eye span, which they use as a sexual display. To investigate eye span development we have compared eye-antennal disc morphology and the expression of three key regulator genes of Drosophila head development, Distal-less ( Dll ) , engrailed ( en ), and wingless ( wg ), in the stalk-eyed flies and Drosophila . We found great similarity in the basic division of the disc into anterior-antennal and posterior-eye portions and in the general patterning of Dll, en , and wg . Unexpectedly, our results showed that although the eye and antenna are adjacent in adult stalk-eyed flies, their primordia are physically separated by the presence of an intervening region between the anterior and posterior portions of the disc. This region is absent from Drosophila eye-antennal discs. We chose two stalk-eyed fly species that differed in the degree of eyestalk exaggeration but surprisingly we found no corresponding difference in the size of the en-wg expression domains that mark the boundaries of the dorsal head capsule primordia. In summary, our expression data establish the regional identity of the eye-antennal disc and provide a framework from which to address the developmental genetics of hypercephaly.     

Identification of methylated sequences in genomic DNA of adult Drosophila melanogaster

The genome of Drosophila melanogaster contains methylated cytosines. Recent studies indicate that DNA methylation in the fruit fly depends on one DNA methyltransferase, dDNMT2. No obvious phenotype is associated with the downregulation of this DNA methyltransferase. Thus, identifying the target sequences methylated by dDNMT2 may constitute the first step towards understanding the biological functions of this enzyme. We used anti-5-methylcytosine antibodies as affinity column to identify the methylated sequences in the genome of adult flies. Our analysis demonstrates that components of retrotransposons and repetitive DNA sequences are putative substrates for dDNMT2. The methylation status of DNA encoding Gag, a protein involved in delivering the transposition template to its DNA target, was confirmed by sodium bisulfite sequencing.     

Structure-specific abnormalities associated with mutations in a DNA replication accessory factor in Drosophila

We have phenotypically and molecularly analyzed the cutlet locus in Drosophila. Homozygous cutlet flies exhibit abnormal development of a subset of adult tissues, including the eye, wing, and ovary. We show that abnormal development of these tissues is due to a defect in normal cell growth. Surprisingly, cell growth is affected in all developing precursor tissues in cutlet mutant animals, including those that give rise to phenotypically wild-type adult structures. The cutlet gene encodes a Drosophila homologue of yeast CHL12 and has similarity to mammalian replication factor C. In addition, cutlet genetically interacts with multiple subunits of Drosophila replication factor C. Our results suggest that the cutlet gene product acts as an accessory factor for DNA replication and has different requirements for the formation of various adult structures during Drosophila development.     

The mean and variance of environmental temperature interact to determine physiological tolerance and fitness

Global climate change poses one of the greatest threats to biodiversity. Most analyses of the potential biological impacts have focused on changes in mean temperature, but changes in thermal variance will also impact organisms and populations. We assessed the combined effects of the mean and variance of temperature on thermal tolerances, organismal survival, and population growth in Drosophila melanogaster. Because the performance of ectotherms relates nonlinearly to temperature, we predicted that responses to thermal variation (±0° or ±5°C) would depend on the mean temperature (17° or 24°C). Consistent with our prediction, thermal variation enhanced the rate of population growth (r(max)) at a low mean temperature but depressed this rate at a high mean temperature. The interactive effect on fitness occurred despite the fact that flies improved their heat and cold tolerances through acclimation to thermal conditions. Flies exposed to a high mean and a high variance of temperature recovered from heat coma faster and survived heat exposure better than did flies that developed at other conditions. Relatively high survival following heat exposure was associated with low survival following cold exposure. Recovery from chill coma was affected primarily by the mean temperature; flies acclimated to a low mean temperature recovered much faster than did flies acclimated to a high mean temperature. To develop more realistic predictions about the biological impacts of climate change, one must consider the interactions between the mean environmental temperature and the variance of environmental temperature.