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MMS induction of different types of genetic damage in Aspergillus nidulans: a comparative analysis in mutagenesis
Abstract:
Methyl methanesulphonate (MMS) was used to test the induction of gene mutation, somatic crossing-over and mitotic non-disjunction in A. nidulans. Gene mutation was tested by inducing mutants resistant to 8-azaguanine and revertants of methG1 in a haploid strain. Somatic crossing-over was tested in heterozygous diploids, both with a selective method, i.e. inducing homozygosis to FPA resistance in a heterozygous fpa A1/+ strain, and with a non-selective method, i.e. identifying the frequencies of colour sectors. This latter method was also used to estimate the induction of non-disjunction because additional markers were present which permitted us to distinguish the two types of colour segregant. Generally, 3 different experimental procedures were used, namely the "plate test", i.e. plating of conidia in agar media containing MMS, and two types of "liquid test", i.e. brief treatment of quiescent or pre-germinated conidia in MMS solution before they were plated on agar media. Point mutations were induced with about equal efficiency with each method, whereas crossing-over was induced preferentially when germinating conidia were exposed to MMS. On the other hand, non-disjunction was induced in germinating and quiescent spores with equal efficiency, but such segregants were not recovered with the selective (fpa) method. The results are discussed for both their practical use in the mutagenic testing procedure and their theoretical implication.
Insights
Methyl methanesulphonate (MMS) induces gene mutations, somatic crossing-over, and mitotic non-disjunction in A. nidulans. MMS exposure methods influenced the induction efficiency of these genetic events.
Area of Science:
- * Genetics
- * Molecular Biology
- * Toxicology
Background:
- * Methyl methanesulphonate (MMS) is a chemical mutagen.
- * Understanding mutagenic mechanisms is crucial for risk assessment.
- * Aspergillus nidulans is a model organism for genetic studies.
Purpose of the Study:
- * To investigate the induction of gene mutation, somatic crossing-over, and mitotic non-disjunction by MMS in A. nidulans.
- * To compare the efficiency of different MMS exposure methods (plate vs. liquid tests).
- * To evaluate the practical and theoretical implications of MMS mutagenicity.
Main Methods:
- * Gene mutation assessed via 8-azaguanine resistance and methG1 reversion in haploid strains.
- * Somatic crossing-over evaluated in heterozygous diploids using selective (FPA resistance) and non-selective (color sectoring) methods.
- * Mitotic non-disjunction analyzed using color segregants in non-selective assays.
- * Three experimental procedures: plate test, liquid test with quiescent conidia, and liquid test with pre-germinated conidia.
Main Results:
- * Point mutations were induced with similar efficiency across all tested MMS exposure methods.
- * Somatic crossing-over was preferentially induced when germinating conidia were exposed to MMS.
- * Mitotic non-disjunction was induced with equal efficiency in both germinating and quiescent spores.
- * Non-disjunctional segregants were not recovered using the selective fpa method.
Conclusions:
- * The method of MMS exposure significantly impacts the induction efficiency of different genetic events.
- * Germinating conidia are more susceptible to MMS-induced somatic crossing-over.
- * Non-disjunction induction is independent of spore germination status but requires specific detection methods.
- * Findings contribute to optimizing mutagenicity testing protocols and understanding MMS genotoxicity.