Mutagen sensitivity of Drosophila melanogaster. I. Isolation and preliminary characterization of a methyl methanesulphonate-sensitive strain

Sensitivity to the monofunctional alkylating agent methyl methanesulfonate (MMS) has been tested as a selection technique to isolate mutant strains which can provide insights into the genetic control of DNA replication, DNA repair and recombination in the complex eucaryote, Drosophila melanogaster. The successful isolation of an X-linked MMS-sensitive strain, mut^s, has suggested that mutagen sensitivity is a feasible methodology for the selection of mutant strains of Drosophila which will be useful in the genetic and biochemical analysis of these cellular functions. Preliminary characterization of this mutant strain indicates that: (A) it is extremely sensitive to killing by MMS; (B) it is more mutable by MMS than the parent wildtype strain; and (C) it appears to possess mutator gene activity.     

The relationship between reaction kinetics and mutagenic action of monofunctional alkylating agents in higher eukaryotic systems. IV. The effects of the excision-defective mei-9L1 and mus(2)201D1 mutants on alkylation-induced genetic damage in Drosophila

Repair-defective mutants of Drosophila melanogaster which identify two major DNA excision repair loci have been examined for their effects on alkylation-induced mutagenesis using the sex-linked recessive lethal assay as a measure of genotoxic endpoint. The alkylating agents (AAs) chosen for comparative analysis were selected on the basis of their reaction kinetics with DNA and included MMS, EMS, MNU, DMN, ENU, DEN and ENNG. Repair-proficient males were treated with the AAs and mated with either excision-defective mei-9L1 or mus(2)201D1 females or appropriate excision-proficient control females. The results of the present work suggest that a qualitative and quantitative relationship exists between the nature and the extent of chemical modification of DNA and the induction of of genetic alterations. The presence of either excision-defective mutant can enhance the frequency of mutation (hypermutability) and this hypermutability can be correlated with the Swain-Scott constant S of specific AAs such that as the SN1 character of the DNA alkylation reaction increases, the difference in response between repair-deficient and repair-proficient females decreases. The order of hypermutability of AAs with mei-9L1 relative to mei-9+ is MMS greater than MNU greater than DMN = EMS greater than iPMS = ENU = DEN = ENNG. When the percentage of lethal mutations induced in mei-9L1 females are plotted against those determined for control females, straight lines of different slopes are obtained. These mei-9L1/mei-9+ indices are: MMS = 7.6, MNU = 5.4, DMN = 2.4, EMS = 2.4 and iPMS = ENU = DEN = ENNG = 1. An identical order of hypermutability with similar indices is obtained for the mus(2)201 mutants: MMS(7.3) greater than MNU (5.4) greater than EMS(2.0) greater than ENU(1.1). Thus, absence of excision repair function has a significant effect on mutation production by AAs efficient in alkylating N-atoms in DNA but no measurable influence on mutation production by AAs most efficient in alkylating O-atoms in DNA. The possible nature of these DNA adducts has been discussed in relation to repair of alkylated DNA. In another series of experiments, the effect on alkylation mutagenesis of mei-9L1 was studied in males, by comparing mutation induction in mei-9L1 males vs. activity in Berlin K (control). Although these experiments suggested the existence of DNA repair in postmeiotic cells during spermatogenesis, no quantitative comparisons could be made.(ABSTRACT TRUNCATED AT 400 WORDS)     

A yeast strain for simultaneous detection of induced mitotic crossing over,mitotic gene conversion and reverse mutation

A diploid yeast strain is described which can be used to study induction of mitotic crossing over, mitotic gene conversion and reverse mutation.Mitotic crossing over can be detected visually as pink and red twin sectored colonies which are due to the formation of homozygous cells of the genotype ade240/ade240 (deep red) and ade-2-119/ade2-119 (pink) from the originally heteroallelic condition ade2-40/ade2-119 which forms white colonies.Mitotic gene conversion is monitored by the appearance of tryptophan non-requiring colonies on selective media. The alleles involved are tryp5-12 and trp5-27 derived from the widely used strain D4.Mutation induction can be followed by the appearance of isoleucine non-requiring colonies on selective media. D7 is homoallelic ilv1-92/ilv1-92. The isoleucine requirement caused by ilv1-92 can be alleviated by true reverse mutation and allele non-specific suppressor mutation.The effects of ethyl methanesulfonate (EMS), nitrous acid, ultraviolet light and hycanthone methanesulfonate were studied with D7 stationary phase cells. Mitotic crossing over as monitored by red/pink twin sectored colonies was almost equally frequent among normal and convertant cells. This showed again that mitotic recombination is not due to the presence fo a few cells committed to meiosis in an otherwise mitotic cell population.The dose-response curves for induction of mitotic gene conversion and reversion of the isoleucine requirement were exponential. In contrast to this, the dose-response curve for induction of twin sectored red and pink colonies reached a plateau at doses giving about 30% cell killing. This could partly be due to lethal segregation in the progeny of treated cells.None of the agents tested would induce only one type of mitotic recombination, gene conversion or crossing over. There was, however, some mutagen specificity in the induction of isoleucine prototrophs.     

Mutagenic responses of five independent geentic loci in CHO cells to a variety of mutagens: Development and characteristics of a mutagen screening system based on selection of multiple drug-resistant markers

With the aime of developing a sensitive mutagen screening system, teh responses of 15 different chemical mutagens at 5 independent genetic loci in Chinese hamster ovary (CHO) cells have been determined. The genetic markers which have been employed include resistance to thioguanine (Thg^r), ouabain (Oua^R), the protein syntheis inhibitor emetime (Emt^r, the plyamine synthesis inhibitor methylglyoxal bisguanylhydrazone (Mbg^r) and the nucleoside analog 5,6-dichlororibofuranosyl benzimidazole (Drb^R). The optimal selection conditions for all of these genetic markers in CHO cells have been described. The chemicals whose response was investigated in these studies include direct-acting alkylating agents (ethyl methanesulfonate, methyl methanesulfonate, β-propiolactone, ethyleneimine,N-nitrosomethylurea and 4-nitroquinolineN-oxide), DNA intercalating and cross-linking agents (ICR-170, acridine orange, ethidium bormide, mitomycin C and actinomycine D), polycyclic hydrocarbons (benzo[a]pyrene (B(a)P) and 7,12-dimethylbenz[a]anthracene (DMBA)) and aromatic amines (benzidine and β-naphthylamine). Simultaneous examination of the response of the set of genetic markers to these chemicals revealed that although all of these chemicals caused a dose-dependent increase in the frequency of mutations at many of the above genetic loci, the magnitude of the mutagenic response at different genetic loci varied greatly depending upon the chemical. Of the genetic loci examined, no one single locus showed higher response to all of the above chemicals, instead, depending upon the chemical, specific loci were found to be more responsive than other. The polycyclic hydrocarbons and aromatic amines were weakly mutagenic in this system at several genetic loci even without any exogenous microsomal activation, although in the presence of a rat liver S9 fraction similar toxic and mutagenic effects of B(a)P and DMBA were observed at 5–20-fold lower concentrations. These results indicate that CHO cells may possess significant capacity for the metabolic activation of many procarnicogens, and also underscore the merits of measuring the mutagenic response at multiple genetic loci in mutagen screening studies.     

Synergistic effect of an Escherichia coli mutator gene on mutagenesis by ultraviolet radiation and by alkylating agents

E. coli strains differing in a gene responsible for high spontaneous mutability (mut HI) were compared for their mutability by UV radiation and by the alkylating agents ethyl methanesulfonate and methyl methanesulfonate. All three exogenous mutagenic agents induced significantly higher frequencies of mutants with impaired carbohydrate-fermenting ability when the mutator allele rather than the wild-type allele was present. Thus the mut HI gene product possibly increases the probability of replication error due to alterations in the structure of the template strand of DNA. An attempt to detect an synergistic effect for UV-induced suppressor mutations was unsuccessful. The failure may have been due to the particular method used for scoring this type of mutation.     

Variation in the physiological sensitivity of maize inbreds to EMS a possible correlation with alcohol dehydrogenase activity

Three inbred lines of maize, AD-1, AD-7 and AD-19, showed significant differences in their physiological sensitivity to ethyl methanesulfonate (EMS). Among the seedling parameters tested, the width of the leaves was the most sensitive and showed the best correlation with the results obtained at maturity. Plant weight was also a good seedling parameter. The physiological sensitivity to EMS was negatively correlated with alcohol dehydrogenase (ADH) activity in the scutellum of the three lines. A possible explanation for this correlation is discussed; however, it may have been due to chance.     

Comparison of radiation-and chemically-induced dominant lethal mutations in male mice

Ionizing radiation-induced dominant lethal mutations in all spermatogenic stages. After irradiation of male mice with 200 R the yield of induced mutations in early spermatids was twice the yield in spermatozoa, late spermatids, and spermatocytes. After irradiation with 400 R or 800 R the spermatocytes were the most sensitive stage for the induction of dominant lethal mutations. The frequency of radiation-induced dominant lethal mutations in postspermatogonial stages was dose-dependent. The yield of dominant lethal mutations in spermatogonia was independent of the dose.     

Complete genome sequence of Beutenbergia cavernae type strain (HKI 0122)

Beutenbergia cavernae (Groth et al. 1999) is the type species of the genus and is of phylogenetic interest because of its isolated location in the actinobacterial suborder Micrococcineae. B. cavernae HKI 0122(T) is a Gram-positive, non-motile, non-spore-forming bacterium isolated from a cave in Guangxi (China). B. cavernae grows best under aerobic conditions and shows a rod-coccus growth cycle. Its cell wall peptidoglycan contains the diagnostic L-lysine ← L-glutamate interpeptide bridge. Here we describe the features of this organism, together with the complete genome sequence, and annotation. This is the first completed genome sequence from the poorly populated micrococcineal family Beutenbergiaceae, and this 4,669,183 bp long single replicon genome with its 4225 protein-coding and 53 RNA genes is part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Permanent draft genome sequence of Dethiosulfovibrio peptidovorans type strain (SEBR 4207)

Dethiosulfovibrio peptidovorans Magot et al. 1997 is the type species of the genus Dethiosulfovibrio of the family Synergistaceae in the recently created phylum Synergistetes. The strictly anaerobic, vibriod, thiosulfate-reducing bacterium utilizes peptides and amino acids, but neither sugars nor fatty acids. It was isolated from an offshore oil well where it was been reported to be involved in pitting corrosion of mild steel. Initially, this bacterium was described as a distant relative of the genus Thermoanaerobacter, but was not assigned to a genus, it was subsequently placed into the novel phylum Synergistetes. A large number of repeats in the genome sequence prevented an economically justifiable closure of the last gaps. This is only the third published genome from a member of the phylum Synergistetes. The 2,576,359 bp long genome consists of three contigs with 2,458 protein-coding and 59 RNA genes and is part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Metronidazole (Flagyl): lack of induction of sister-chromatid exchanges in CHO-K1 cells

328 X-linked recessive lethal mutations induced in late spermatids by hycanthone methanesulfonate were tested for coverage by duplications that comprised, in total, about 24% of the euchromatic X chromosome; 78 lethals appeared to be covered. Crossover localization tests of a random sample of 38 non-covered lethals revealed 4 chromosomes carrying a lethal within a duplicated segment. Lethals localized to a particular region were crossed to reference deficiencies and single-locus mutations, and inter se, to ascertain their genetic extent. The proportion of multi-locus deletions among these 78 covered and 4 non-covered lethals was 3/48, 1/10 and 13/24 for the distal, medial and proximal regions, respectively. A storage period of 9 days did not noticeably influence these proportions. In the sample of 38 non-covered lethals, and among 17 of the covered single-site lethals, 4 cases of strong crossover suppression were detected. Comparison of these results with data obtained with other mutagens suggests that induction of multi-locus deletions, and possibly of other types of chromosome rearrangement, could in part depend on other mechanisms than those acting in the formation of translocations and chromosome loss. For the purpose of mutagen testing, these findings imply that, in Drosophila, results in the regular genetic tests for chromosome breakage events do not always accurately predict the capacity of a mutagen to induce multi-locus deletions. This is of importance since transmissible multi-locus deletions have been considered a significant source of genetic damage in man.     

Estimation of the effects of chemical mutagens: Lessons from radiation genetics

Years of work with ionizing radiations have given us a wealth of data on radiation-induced mutations. These data, which have given insights regarding the mutational processes, should form the background for all mutagenesis work. In chemical mutagenesis, as in radiation mutagenesis, it is important to know the shape of the dose-effect curve in order to make further interpretations and calculations. It is also important to be on the constant alert for new relations that can be explored.     

Comparative proteogenomic analysis of the Leptospira interrogans virulence-attenuated strain IPAV against the pathogenic strain 56601

The virulence-attenuated Leptospira interrogans serovar Lai strain IPAV was derived by prolonged laboratory passage from a highly virulent ancestral strain isolated in China. We studied the genetic variations of IPAV that render it avirulent via comparative analysis against the pathogenic L. interrogans serovar Lai strain 56601. The complete genome sequence of the IPAV strain was determined and used to compare with, and then rectify and reannotate the genome sequence of strain 56601. Aside from their highly similar genomic structure and gene order, a total of 33 insertions, 53 deletions and 301 single-nucleotide variations (SNVs) were detected throughout the genome of IPAV directly affecting 101 genes, either in their 5' upstream region or within their coding region. Among them, the majority of the 44 functional genes are involved in signal transduction, stress response, transmembrane transport and nitrogen metabolism. Comparative proteomic analysis based on quantitative liquid chromatography (LC)-MS/MS data revealed that among 1 627 selected pairs of orthologs, 174 genes in the IPAV strain were upregulated, with enrichment mainly in classes of energy production and lipid metabolism. In contrast, 228 genes in strain 56601 were upregulated, with the majority enriched in the categories of protein translation and DNA replication/repair. The combination of genomic and proteomic approaches illustrated that altered expression or mutations in critical genes, such as those encoding a Ser/Thr kinase, carbon-starvation protein CstA, glutamine synthetase, GTP-binding protein BipA, ribonucleotide-diphosphate reductase and phosphate transporter, and alterations in the translational profile of lipoproteins or outer membrane proteins are likely to account for the virulence attenuation in strain IPAV.     

Complete genome sequence of Nakamurella multipartita type strain (Y-104)

Nakamurella multipartita (Yoshimi et al. 1996) Tao et al. 2004 is the type species of the monospecific genus Nakamurella in the actinobacterial suborder Frankineae. The nonmotile, coccus-shaped strain was isolated from activated sludge acclimated with sugar-containing synthetic wastewater, and is capable of accumulating large amounts of polysaccharides in its cells. Here we describe the features of the organism, together with the complete genome sequence and annotation. This is the first complete genome sequence of a member of the family Nakamurellaceae. The 6,060,298 bp long single replicon genome with its 5415 protein-coding and 56 RNA genes is part of the Genomic Encyclopedia of Bacteria and Archaea project.     

The effects of radiation exposure-rate and exposure fractionation on the frequencies of recessive and dominant lethals in immature oocytes of Drosophila melanogaster

A measure of seedling viability was used to estimate the homozygous geneticc load of seedlings from mutagenized populations of Oenothera. The breeding protocol forced genomes to homozygosity. Pollen from control and mutagenized Oenothera hookeri T. and G. strain Johansen, a seven-paired lethal-free stock, was used to pollinate a translocation stock with balanced lethals. The hybrid formed a complete translocation ring and upon selfing yielded two types of plants, a translocation heterozygote similar to its hybrid parent and a seven-paired plant homozygous for the 7 chromosomes obtained from Johansen. Genetic markers allowed the identification of seven-paired seedlings in the cotyledon stage. Control hybrids averaged a recovery of 57.5% seven-paired seedlings. Hybrids obtained from plants that had been mutagenized by seed treatment with 15000 R X-rays, 0.04 M ethyl methanesulfonate (EMS), and 0.08 M EMS averaged 48.3%, 19.2%, and 6.0% recovery of seven-paired forms, respectively. The data are used to estimate the genetic load and lethal equivalents in each population. The implications of these results are evaluated with reference to mutation breeding of plant populations.     

Hydroxylamine-induced purple adenine (ad-3) mutants in Neurospora crassa. I. Characterization of mutants by genetic tests

The genetic effects of hydroxylamine (HA) on Neurospora crassa were studied in an effort to understand the difference between the results obtained on very simple prokaryotic systems and those obtained with mammalian systems. A 2-component heterokaryon was used to study the inactivation of conidia and the induction of recessive lethal mutations at specific loci and over the entire genome. The heterokaryon is heterozygous for 2 closely linked loci, ad-₃A and ad-₃B, in the ad-₃ region. Specific locus mutations can result from either point mutation or chromosome deletion. The results were as follows: (1) Both homokaryotic and heterokaryotic conidia had multi-hit survival curves, and there was no difference between the survival levels of the two as a function of treatment time. (2) The frequency of recessive lethal mutations in the ad-₃ region increased as the square of treatment time.     

Mutagenesis at the ad-3A and ad-3B loci haploid UV-sensitive strains of Neurospora crassa. III. Comparison of dose-response curves for inactivation and mutation induced by gamma-rays

Gamma-Ray-induced inactivation and induction of mutations at the ad-3A and ad-3B loci of Neurospora crassa have been compared among 6 different UV-sensitive strains and a standard wild-type strain. The 6 strains show varying degrees of sensitivity to gamma-ray-induced inactivation, with the relative sensitivity at 37% survival being uvs-6 greater than upr-1 greater than uvs-2 greater than uvs-3 greater than wild-type greater than uvs-5 greater than uvs-4. Studies on the induction of ad-3 mutants by gamma-rays show that when the dose-response curve (expressed in terms of ad-3 mutants among the surviving colonies) of the UV-sensitive strains are compared with wild-type, the 2 excision-repair-deficient mutants uvs-2 and upr-1 exhibit enhanced ad-3 mutant frequencies, uvs-3 exhibits reduced ad-3 mutant frequencies whereas both uvs-4 and uvs-5 show lower mutant frequencies than wild-type.