Isolation and characterization of repair-deficient mutants of Drosophila melanogaster

DNA Repair in Drosophila: Mutagens, Models, and Missing Genes

The numerous processes that damage DNA are counterbalanced by a complex network of repair pathways that, collectively, can mend diverse types of damage. Insights into these pathways have come from studies in many different organisms, including Drosophila melanogaster Indeed, the first ideas about chromosome and gene repair grew out of Drosophila research on the properties of mutations produced by ionizing radiation and mustard gas. Numerous methods have been developed to take advantage of Drosophila genetic tools to elucidate repair processes in whole animals, organs, tissues, and cells. These studies have led to the discovery of key DNA repair pathways, including synthesis-dependent strand annealing, and DNA polymerase theta-mediated end joining. Drosophila appear to utilize other major repair pathways as well, such as base excision repair, nucleotide excision repair, mismatch repair, and interstrand crosslink repair. In a surprising number of cases, however, DNA repair genes whose products play important roles in these pathways in other organisms are missing from the Drosophila genome, raising interesting questions for continued investigations.

A germline clone screen on the X chromosome reveals novel meiotic mutants in Drosophila melanogaster

In an effort to isolate novel meiotic mutants that are severely defective in chromosome segregation and/or exchange, we employed a germline clone screen of the X chromosome of Drosophila melanogaster. We screened over 120,000 EMS-mutagenized chromosomes and isolated 19 mutants, which comprised nine complementation groups. Four of these complementation groups mapped to known meiotic genes, including mei-217, mei-218, mei-9, and nod. Importantly, we have identified two novel complementation groups with strong meiotic phenotypes, as assayed by X chromosome nondisjunction. One complementation group is defined by three alleles, and the second novel complementation group is defined by a single allele. All 19 mutants are homozygous viable, fertile, and fully recessive. Of the 9 mutants that have been molecularly characterized, 5 are canonical EMS-induced transitions, and the remaining 4 are transversions. In sum, we have identified two new genes that are defined by novel meiotic mutants, in addition to isolating new alleles of mei-217, mei-218, mei-9, and nod.

Proteomic analysis of honeybee (Apis mellifera L.) pupae head development

The honeybee pupae development influences its future adult condition as well as honey and royal jelly productions. However, the molecular mechanism that regulates honeybee pupae head metamorphosis is still poorly understood. To further our understand of the associated molecular mechanism, we investigated the protein change of the honeybee pupae head at 5 time-points using 2-D electrophoresis, mass spectrometry, bioinformatics, quantitative real-time polymerase chain reaction and Western blot analysis. Accordingly, 58 protein spots altered their expression across the 5 time points (13–20 days), of which 36 proteins involved in the head organogenesis were upregulated during early stages (13–17 days). However, 22 proteins involved in regulating the pupae head neuron and gland development were upregulated at later developmental stages (19–20 days). Also, the functional enrichment analysis further suggests that proteins related to carbohydrate metabolism and energy production, development, cytoskeleton and protein folding were highly involved in the generation of organs and development of honeybee pupal head. Furthermore, the constructed protein interaction network predicted 33 proteins acting as key nodes of honeybee pupae head growth of which 9 and 4 proteins were validated at gene and protein levels, respectively. In this study, we uncovered potential protein species involved in the formation of honeybee pupae head development along with their specific temporal requirements. This first proteomic result allows deeper understanding of the proteome profile changes during honeybee pupae head development and provides important potential candidate proteins for future reverse genetic research on honeybee pupae head development to improve the performance of related organs.

A large-scale screen for mutagen-sensitive loci in Drosophila

In a screen for new DNA repair mutants, we tested 6275 Drosophila strains bearing homozygous mutagenized autosomes (obtained from C. Zuker) for hypersensitivity to methyl methanesulfonate (MMS) and nitrogen mustard (HN2). Testing of 2585 second-chromosome lines resulted in the recovery of 18 mutants, 8 of which were alleles of known genes. The remaining 10 second-chromosome mutants were solely sensitive to MMS and define 8 new mutagen-sensitive genes (mus212-mus219). Testing of 3690 third chromosomes led to the identification of 60 third-chromosome mutants, 44 of which were alleles of known genes. The remaining 16 mutants define 14 new mutagen-sensitive genes (mus314-mus327). We have initiated efforts to identify these genes at the molecular level and report here the first two identified. The HN2-sensitive mus322 mutant defines the Drosophila ortholog of the yeast snm1 gene, and the MMS- and HN2-sensitive mus301 mutant defines the Drosophila ortholog of the human HEL308 gene. We have also identified a second-chromosome mutant, mus215(ZIII-2059), that uniformly reduces the frequency of meiotic recombination to <3% of that observed in wild type and thus defines a function required for both DNA repair and meiotic recombination. At least one allele of each new gene identified in this study is available at the Bloomington Stock Center.

Search for DNA repair pathways in Drosophila melanogaster

The knowledge about the existence of different pathways for the repairing of DNA lesions has made possible a better understanding of mutation processes. The double mutant method has been shown to be useful for grouping rad mutants in yeast. Through this method, three different groups of repair mechanisms were found: (a) RAD3 group corresponding to the excision repair of UV lesions, (b) RAD6 group corresponding to the translesion type of post-replication repair and (c) RAD52 group corresponding to the recombination type of post-replication repair. In this work, a search for a classification of Drosophila mus mutants in groups analogous to yeast RAD groups is done. Information obtained by double mutant studies was integrated with that obtained by biochemical, recombination, DNA damaging agent sensitivity and mutation studies. The following groups were found: (a) group of mei9 and mus201, analogous to RAD3, (b) group of mei41 and mus302 analogous to RAD52 and, (c) group of mus104 and mus101 analogous to RAD6. In addition, there are mutants that belong to a group corresponding to pre-replication repair of MMS lesions such as mus103, mus306 and mus207. As a peculiarity of Drosophila, it was found that interaction between pre- and post-replication repair mechanisms is indifferent and not synergistic as was found in yeast. A possible explanation could be a weaker control of post-replication repair mechanisms in Drosophila than in yeast. It is expected that this research could help for a better understanding of repair mechanisms in complex organisms.

Apurinic endonuclease activity remains constant during early Drosophila development

An endonuclease activity that acts on alkali-labile lesions in x-irradiated PM2 DNA and recognizes apurinic lesions in heat/acid treated DNA has been partially purified from Drosophila melanogaster embryos and its specific activity monitored throughout early development. The enzyme activity also showed a low level of activity on UV-irradiated DNA. The saturation kinetics observed with both x-irradiated and apurinic PM2 DNA substrates were similar. The endonuclease activity exhibited a broad pH optimum between pH 6 and 8.5 and was almost completely inhibited by 100 mM NaCl, 0.1 mM EDTA, 2 mM CaCl2 and 10 mM NEM. The reaction was not completely dependent on the presence of Mg++cation, but optimum activity was obtained at a concentration of 0.1 mM; concentrations greater than 1 mM Mg++ were inhibitory. The specific activity of the apurinic endonuclease, partially purified from several stages of embryonic and early larval development, remained the same. Unfertilized eggs exhibited a reduced level of this presumptive repair activity.

The DNA transposition system of hybrid dysgenesis in Drosophila melanogaster can function despite defects in host DNA repair

Genetic traits associated with the hybrid dysgenesis syndrome were quantified in strains deficient in two major host-coded DNA repair pathways, post-replication and excision repair. A defect in either (or both) pathway(s) fails to influence the frequency of male recombination or sex-linked recessive lethal mutations associated with hybrid dysgenesis, suggesting that the DNA transposable elements associated with this syndrome act independently of these cellular functions. However, when the post-replication repair pathway is blocked, the recovery of second chromosomes containing factors associated with hybrid dysgenesis activity is reduced. The decrease in recovery is associated with zygotic lethality.

Mutagen sensitivity of Drosophila melanogaster. V. Identification of second chromosomal mutagen sensitive strains

Six recessive second chromosomal mutants of Drosophila melanogaster exhibiting larval hypersensitivity to methyl methanesulfonate have been identified and assigned to six complementation groups. The strains have been analyzed for their sensitivities to UV, X-ray, nitrogen mustard and formaldehyde. Two classes of mutants not previously observed in Drosophila have been identified. The mus 204A1 and mus 205A1 mutants exhibit sensitivity to MMS and UV but not X-ray or nitrogen mustard, while the mus 206A1 and mus 207A1 mutants display sensitivity to MMS, UV, and nitrogen mustard. Four of the seven strains exhibit poor female fertility and two of these are shown to have a weak meiotic disjunctional defect. Biochemical studies of the mus 205A1 mutant suggest a defect in DNA synthetic ability associated with excision and postreplication repair performed on UV and alkylation-damaged templates (Boyd and Harris 1981; Brown and Boyd 1981 b; R.L. Dusenbery, manuscript in preparation).

Effects of radiation on the survival of excision-defective cells from Drosophila melanogaster

The effect of various doses of ultraviolet light and ionizing radiation on the survival of excision-defective Drosophila cells has been determined by cloning treated and untreated cells in agarose. Although excision-defective cells survive moderate amounts of DNA damage, they display a severe hypersensitivity to both types of radiation relative to excision-proficient cells. Exposure of ultraviolet-irradiated cells to fluorescent light results in a reduction of the density of pyrimidine dimers in cellular DNA and a 10-to 20-fold increase in survival. Parallel analysis of dimer density and survival, however, suggests that much of the lethal effect of ultraviolet light is due to nondimer damage. Cell proliferation was monitored in both excision-proficient and excision-defective cells exposed to doses of ultraviolet light that reduced survival by 90%. Under these conditions excision-proficient cells displayed exponential growth whereas excision-defective cells exhibited no cell proliferation for 12 days.

mus(3)312D1, A mutagen sensitive mutant with profound effects on female meiosis in Drosophila melanogaster

The third chromosome, mutagen sensitive mutant mus(3)312D1 impairs the meiotic process in females by increasing the frequency of first division nondisjunction and decreasing the frequency of meiotic crossing over. These genetic properties connote 312 to be defective in DNA replication and/or repair intimately associated with the crossing over exchange process. The mutant maps to the left arm of chromosome III between ru and h, and represents a new genetic site for a meiotic mutant.

Mutants partially defective in excision repair at five autosomal loci in Drosophila melanogaster

Primary cell cultures derived from mutants in seventeen different genes were analyzed for their ability to excise pyrimidine dimers from DNA. Five of these mutagen-sensitive mutants [mus(2)205A1, mus(3)302D1, mus(3)304D3, mus(3)306D1, mus(3)308D2] display a significantly reduced excision capacity relative to control cultured. In addition, two of the five [mus(3)306D2, mus(3)308D2] are defective in the accumulation of single-strand breaks normally seen after ultraviolet irradiation. This study, therefore, brings the total number of Drosophila mutants known to be defective in excision repair to seven. The results are discussed relative to other genetic and biochemical properties of these mutants.

Repair in fertilized eggs of mice and its role in the production of chromosomal aberrations

The fertilized egg may influence the yield of dominant-lethal mutations produced from chemical treatment of male postmeiotic germ cells to a small or large extent depending upon the mutagen used and the competence of the egg to repair the premutational lesions induced. The strain of females has little influence on the yield of dominant-lethal mutations induced by triethylenemelamine or ethyl methane-sulfonate in spermatids and spermatozoa, but it has a large influence in the case of isopropyl methanesulfonate. In addition to this difference, triethylenemelamine and ethyl methanesulfonate induce high levels of heritable translocations at these germ cell stages whereas isopropyl methanesulfonate is practically ineffective, even though doses of these chemicals produced comparable levels of dominant-lethal mutations. These differences between ethyl methanesulfonate and triethylenemelamine on one hand and isopropyl methanesulfonate on the other were hypothesized to be a function of the types of chromosomal lesions present at the time of repair activity and whether or not chromosomal aberrations were already fixed at the time of postfertilization pronuclear DNA synthesis.