Interspecific comparison of ethyl methanesulfonate-induced mutation rates in relation to genome size

Influence of the presence of B chromosomes on DNA damage in Crepis capillaris

The sensitivity of different plant species to mutagenic agents is related to the DNA content and organization of the chromatin, which have been described in ABCW and bodyguard hypotheses, respectively. Plant species that have B chromosomes are good models for the study of these hypotheses. This study presents an analysis of the correlation between the occurrence of B chromosomes and the DNA damage that is induced by the chemical mutagen, maleic hydrazide (MH), in Crepis capillaris plants using comet assay. The presence of B chromosomes has a detectable impact on the level of DNA damage. The level of DNA damage after MH treatment was correlated with the number of B chromosomes and it was observed that it increased significantly in plants with 3B chromosomes. We did not find evidence of the protective role from chemical mutagens of the constitutive heterochromatin for euchromatin in relation to DNA damage. The DNA damage involving the 25S rDNA sequences was analyzed using the comet-FISH technique. Fragmentation within or near the 25S rDNA involved the loci on the A and B chromosomes. The presence of B chromosomes in C. capillaris cells had an influence on the level of DNA damage that involves the 25S rDNA region.

A comparative study of the antimutagenic effects of antioxidants on chemical mutagenesis in Drosophila melanogaster

The 1,4-dihydropyridine derivative 2,6-dimethyl-3,5-diethoxycarbonyl-4-(Na carboxylate)-1,4-dihydropyridine (1,4-DHP) was studied for antimutagenic effects in the dominant lethal test and in the sex-linked recessive lethal test of Drosophila melanogaster. The observed effects were compared with those of the radioprotectors cysteine and cysteamine and with those of the phenolic antioxidant butylated hydroxytoluene (BHT). In a wide range of concentrations, including low ones, 1,4-DHP reduces the frequency of EMS-induced genetic damage (point mutations and chromosome breakage). A reduction of the mutation rate induced by EMS in adults could be observed independently of the developmental stages (larvae or imago) pretreated with 1,4-DHP. The protective effect of this new antimutagen against the alkylating agent depended on both the 1,4-DHP dose and the level of the EMS-induced mutation rate. The effect of 1,4-DHP was more pronounced than that of the studied radioprotectors. It is concluded that dihydropyridine-type compounds are able to protect eukaryote germs cells from genetic damage produced by direct-acting mutagens such as EMS.

Apparent resistance to mutagenesis by ionizing radiation, and some other unusual responses

It is pointed out that in some species it is very difficult or even apparently impossible to get genetic visible marker mutants by means of ionizing radiation. Such results are not as a rule published. Species in which no mutants at all could be obtained, after what seem to be adequate efforts by several geneticists are Limnaea peregra, Rhynchosciara angelae, Coelopa frigida, Oncopeltus fasciatus, Dermestes maculatus. Published data on Sciara, Tribolium, Blattella, in which a relative difficulty in getting mutants is reported, are discussed and compared to many other forms in which obtaining marker mutants is on the contrary easy. What appears to be very abnormal mutagenesis is described in Drosophila busckii, which yielded an unusual frequency of autosomal dominants, and Drosophila nebulosa, in which only very poor mutants could be obtained. Possible reasons for all these departures from the usual are discussed. No firm conclusions are reached, but one is led to consider the possible effects of overall chromosome structure, presence or absence of heterochromatin, and multiplicity at the single locus or single polytene band level. There seems to be no relation between the rates of induction of dominant lethality and of point mutation for visible markers.

Radiation equivalence of genotoxic chemicals. Validation in cultured mammalian cell lines

Published data on mutations induced by ionizing radiation and 6 monofunctional alkylating agents, namely EMS, MMS, ENNG, MNNG, ENU and MNU, in different cell lines (Chinese hamster ovary, Chinese hamster lung V79, mouse lymphoma L5178 and human cells) were analysed so that radiation-equivalent chemical (REC) values could be calculated. REC values thus obtained for a given alkylating agent with different cell lines fall within a narrow range suggesting its validation in cultured mammalian cell systems including human.

Induction of nuclear anomalies (micronuclei) in the peripheral blood erythrocytes of the eastern mudminnow Umbra pygmaea by ethyl methanesulphonate

In a short feasibility study, we detected the induction of nuclear anomalies in the peripheral blood erythrocytes of fish by the genotoxic compound ethyl methanesulphonate. Exposure of the eastern mudminnow Umbra pygmaea to the compound gave rise to nuclear segments resembling the particles found in mammalian micronucleus tests, but also to irregular Feulgen-positive structures in the cytoplasm. Further studies with fish erythrocytes are recommended for investigating whether the monitoring of nuclear anomalies is a suitable and rapid method for the detection of genotoxic compounds in the aquatic environment.

EMS- and radiation-induced mutation frequencies at individual loci in Arabidopsis thaliana (L.) Heynh

Average mutation frequencies per locus per dose of mutagen - EMS, X-rays and fast neutrons - were estimated from 15 different loci of Arabidopsis thaliana. These loci relate to clearly distinguishable phenotypic mutant groups, each affected by a limited number of loci. There were significant differences in mutation rate between individual loci. The proposition of a linear relationship between DNA content and mutation frequency per locus is rejected.