Studies on the inhibition and mutation of Aspergillus nidulans by acridines

Dyes in aquaculture and reference points for action

The European Commission requested EFSA to evaluate whether a series of dyes are covered by the ‘Guidance on methodological principles and scientific methods to be taken into account when establishing Reference Points for Action (RPAs) for non‐allowed pharmacologically active substances present in food of animal origin’ and to which group they should be attributed according to this guidance. Although these substances are not registered for use in food‐producing animals in the European Union, they may be used illegally in aquaculture for their antimicrobial properties. It was concluded that acriflavine, 3‐aminoacridine, aminoacridine, basic blue 7, brilliant green, leucobrilliant green, C.I. basic blue 26, chloranil, crystal violet, leucocrystal violet, dichlone, ethyl violet, methylene blue, new methylene blue, Nile blue, pararosaniline base, proflavine, proflavine hydrochloride, rhodamine 6G and trypan red are covered by the guidance document and belong to group I. A toxicological screening value of 0.0025 μg/kg body weight per day is applicable. Azure blue and potassium permanganate were excluded from the evaluation due to their inorganic nature.

Systems and results of tests for chemical induction of mitotic malsegregation and aneuploidy in Aspergillus nidulans

In Aspergillus several types of test systems have been developed for detection of chemicals which induce aneuploidy and/or malsegregation of chromosomes. Results from 23 papers were reviewed in which numerical data for 42 chemicals had been reported. The test systems fall into two groups. One group includes all purely genetic tests that detect euploid mitotic segregants from heterozygous diploids and identify these either as products of malsegregation of chromosomes or as products of crossing-over (13 papers, several reviewed in detail previously; Käfer et al. (1982) and Scott et al. (1982)). The other group includes tests that treat haploid or diploid strains and detect aneuploids as unstable abnormally growing segregants which can be identified as specific disomics or trisomics by their characteristic phenotypes. In addition, such tests characterize abnormal segregants from heterozygous diploids by correlating phenotypes with patterns of genetic segregation in spontaneous euploid sectors. This analysis makes it possible to distinguish between induced primary aneuploidy of whole chromosomes and partial tri- or monosomy resulting from chromosome breakage and secondary spontaneous malsegregation (10 papers). Based on results of both types of tests, it is postulated that chemicals which cause increases of euploid malsegregants, but not of crossovers, normally induce aneuploids as primary products (as shown for 7 of the 14 cases). These include compounds which damage spindles or membranes (especially the well-known haploidizing agents) and generally are effective only when growing cells are exposed. (8 chemicals that may belong in this category could not be classified for certain, because information was insufficient.) On the other hand, chemicals which cause increases of all types of euploid segregants (11 cases), mostly induce drastic mutations and aberrations as primary effects and cause spontaneous malsegregation or crossing-over only as secondary events (as demonstrated for radiation-induced abnormals). In addition, a few chemicals were negative, because they increased only crossing-over or showed no increased segregation at all at concentrations which reduced survival or growth rate (9 cases). Recommendations are made for standardization of methods and protocols. New tester strains and specific procedures are outlined which should be useful for conclusive tests of chemicals that may induce aneuploidy.

The effect of dose and time on the induction of genetic alterations in Saccharomyces cerevisiae by aminoacridines in the presence and absence of visible light irradiation in comparison with the dose-effect-curves of mutagens with other type of action

Aminoacridines induce frameshift mutations and are photodynamically active, depending on whether visible light is absent or present. Therefore, a test system which allows to compare quantitatively the genetic effects of aminoacridines irradiated or unirradiated by visible light ought to be susceptible to the different DNA alterations which can be induced by these substances. For this reason in most experiments mitotic gene conversion and only in some selected experiments reverse mutation was chosen as the indicator of genetic activity. In contrast to mutation systems mitotic gene conversion has never shown a response specific to only some types of mutagens. The three aminoacridine derivatives used-acridine orange (AO), proflavine (PF), and acridine yellow (AY)-were successful in the induction of convertants at two different loci. No locus-specificity could be observed. The time-dependent induction of convertants proceeds quickly but soon reaches-especially after treatment without light-a saturation point. The dose/effect-curve after treatment in the dark has a slope increasing with increasing concentration. Irradiation with visible light results in a dose/effect-curve consisting of three parts. Af first the increase of convertants is nearly linear extending one (AY) to three (AO) orders of magnitude. After a saturation effect begins at the point at which an effectiveness of the acridines in the dark is apparent. At high concentrations an induction of convertants can again be observed which is nearly the same as that after treatment in the dark. To determine whether the dose/effect-curves obtained for gene conversion refer to similar curves for gene mutations after treatment with AO at the same locus not only gene conversions but also reverse mutations were scored for. AO-treatment in the dark is ineffective in inducing reverse mutations. Irradiation with visible light results in a dose/effect-curve beeing parallel only in its first part to the dose/effect-curve obtained for gene conversion, while in its second part a mutation frequency decline can be observed. Comparing the dose/effect-curves of AO resulting from the induction of gene conversion and gene mutation, and taking into account that no mutants can be induced by AO-treatment in the dark, the increase in convertants at high acridine-concentrations can be explained as an addition of light-dependent and light-independent effects. That means, in mutation systems at low concentrations of aminoacridines irradiation with visible light should cause transitions, transversions and microlesions, at intermediate concentrations frameshift lesions should begin to appear, and at very high concentrations nearly exclusively frameshift lesions should occur. The dose/effect-curves of aminoacridines compared with those of other mutagens are very complex. The dose/effect-curves of the mutagens of other type of action tested are linear in a double logarithmic scale, and parallel for induced gene conversion and induced gene mutation...

Mitotic non-conformity in Aspergillus: successive and transposable genetic changes

Strains ofAspergillus nidulanswith, a duplicate chromosome segment are mitotically unstable; in addition to phenotypically improved variants, arising following deletions in either duplicate segment, they give morphologically deteriorated types, some with, enhanced stability. In one isolate, deterioration and increased instability were determined by mutation in a duplicate segment; a more stable derivative no longer had this mutation but had one in another linkage group. Another variant, too unstable for analysis, gave derivatives whose single, new mutations were in different linkage groups. It is proposed that deterioration and increased instability result from tandem duplications on either duplicate segment; transposition of these to non-duplicated regions reduces instability. Another 17 variants had a single new mutation each; mutations, possibly clustered, occurred in all linkage groups. In these strains perhaps transposition preceded analysis. Deteriorated variants gave lineages of types with morphological changes caused by further, superimposed mutations. This continued instability is explained as interaction, in fidelity of replication, of non-homologous chromosome segments.

Instability inA. nidulansstems from chromosome imbalance. As imbalance is known or suspected in other cases of instability it may be possible to show common mechanisms for apparently diverse phenomena.

Analysis of the genetic instability induced by nitrous acid in Schizosaccharomyces pombe

A pedigree analysis of several cell-colony generations following a mutagenic treatment with nitrous acid has shown that in S. pombe a genetic instability is produced that replicates several times and produces a mutation in independent lines.

It has been shown that the mutants isolated in the progeny of a mosaic colony all contain a genetic alteration that cannot be resolved by genetic analysis and therefore the mutations have occurred at the same genetic site. This finding is confirmed by interallelic complementation and phenotypic analyses.

Chromosome instability related to gene suppression in Aspergillus nidulans

A complicated system of chromosome instability related to gene suppression has been analysed. In addition, unstable genetic events analogous to those previously described inA. nidulansand in other organisms have been detected and one type of unstable variant recovered may be determined by V-type position effect. Furthermore, the selective systems used, clearly offer scope for analysis of genetic instability in general.