INDUCED BACK-MUTATIONS IN A SPECIFIC GENE OF NEUROSPORA CRASSA

Genomic Sequencing To Identify Potential Causative Mutation(s) of Neurospora crassa col-4

In many cases, genes for commonly used genetic markers in model organisms have not been identified; therefore, it is of interest to identify the causative genes. Whole-genome sequencing was used to identify potential causative mutations for a col-4 allele of Neurospora crassa.

In many cases, genes for commonly used genetic markers in model organisms have not been identified; therefore, it is of interest to identify the causative genes. Whole-genome sequencing was used to identify potential causative mutations for a col-4 allele of Neurospora crassa.

The origins of the back-mutation assay method: a personal recollection

The back-mutation assay method for determining the mutagenicity of various treatments was first developed a little over 50 years ago and has been in continuous use ever since. Shortly after the method was first used it became evident that certain factors of cell density, composition of media, etc., had to be carefully controlled to preserve an acceptable reliability of the method. A factor of particular importance was the suppression of growth of back-mutant prototrophic cells by the large number of auxotrophic cells present, a phenomenon which later became known as the "Grigg Effect." This review describes the origins of the back-mutation method and of the confounding competitive suppression phenomenon, the cause of competitive suppression, methods of diagnosing whether it is likely to bias the interpretation of a particular back-mutation experiment, and an experimental design which removes it entirely as a possible source of error. A number of other phenomena, such as phenotypic lag and coincident mutation associated with back-mutation, are also discussed as possible sources of error.

Mutation tests in Neurospora crassa. A report of the U.S. Environmental Protection Agency Gene-Tox Program

Many mutation tests have been developed in Neurospora crassa during the almost 40 years of its use in mutation research. These tests detect two major classes of mutation: gene mutation and meiotic nondisjunction. Within the first class, forward- and reverse-mutation tests have been used. The forward-mutation tests include those that detect mutations at many loci and at specific loci. Both kinds of forward-mutation tests have been done in homokaryons (n) and heterokaryons (n + n'). From the publications that were not rejected by our pre-established criteria, data were extracted for 166 chemicals that had been tested for mutagenicity. Only 6 of the 166 chemicals have been tested in one or more gene mutation test and the meiotic nondisjunction test; these 6 chemicals were positive in the first and negative in the second. Of the 102 chemicals tested in one or more gene mutation tests, 94 were positive and 8 were negative. Of the 70 chemicals tested in the meiotic nondisjunction test, 7 were positive and 63 were negative. Two tests, the ad-3 forward-mutation test and the meiotic nondisjunction test, have been used most frequently. These two tests are especially important for hazard evaluation, because each detects a class of mutations that is likely to be deleterious or lethal in the F1 - disomics by the meiotic nondisjunction test and multilocus deletions by the ad-3 forward-mutation test in heterokaryons. Generally, direct-acting chemicals are mutagenic in the gene mutation tests, but few chemicals that required metabolic activation have been tested. Only 31 of the 166 chemicals tested in N. crassa have been tested for carcinogenicity. Among these chemicals, there is a good association between mutagenicity in gene mutation tests and carcinogenicity but a poorer association between meiotic nondisjunction and carcinogenicity; however, only a small number of chemicals has been tested in the meiotic nondisjunction test. Further use and development of certain mutation tests in N. crassa are desirable.

The use of Neurospora in the evaluation of the mutagenic activity of environmental chemicals

The utility of various assay systems developed with Neurospora for hazard identification, hazard evaluation, and risk estimation is discussed. The use of the ad-3 test system in a two-component heterokaryon is discussed in relation to its utility for hazard evaluation and risk estimation. This ad-3 assay provides information on those specific locus mutations that arise by multilocus deletions with regard to both frequency and relative size. Information on this class of specific locus mutations is particularly important because, as shown in Drosophila, mouse, and man, this type of damage can have immediate and undesirable effects on F1 progeny.

Surface tension activity and paramorphogenic effect of sorbose, sodium desoxycholate, and griseofulvin on the growth of colonies of Chaetomium aureum Chivers

Sorbose at 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0% levels, sodium-desoxycholate at 0.025, 0.050, 0.075, 0.1 and 0.125% levels, and griseofulvin at 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, and 0.010% levels restrict the growth of colonies of Chaetomium aureum, both at pH 6.5 and 7.0. Restriction of colonies was most effective with 0.7% sorbose, 0.1% sodium-desoxycholate, and 0.006% griseofulvin in the medium adjusted to pH 6.5. Surface tension activity of sorbose, sodium-desoxycholate, and griseofulvin in different concentrations was determined, following the usual standard method.