title: Development of a specific-locus assay in the ad-3 region of two-component heterokaryons of Neurospora: a review.
abstract: In recognition of the need for a more comprehensive data base for genetic risk assessment of human exposure to mutagenic agents in the environment, a model system was developed for specific-locus studies in Neurospora crassa. This lower eukaryotic organism permits the utilization of microbial techniques for recovery of large numbers of specific-locus mutations at two closely linked loci as well as their subsequent genetic analysis. In particular, this assay makes possible exploratory experiments with different environmental mutagens to obtain data on a wide variety of experimental conditions. Such data make it possible to study induction kinetics and mutational spectra in a manner that is not as yet feasible in higher eukaryotic organisms. The adenine-3 (ad-3) specific-locus assay was modeled after the 2-gene, morphological specific-locus assay in the dilute-short-ear region of the mouse, and it also detects forward-mutations at two closely linked loci, namely, ad-3A and ad-3B. Because ad-3 mutations are recovered by a direct method, based on the accumulation of a reddish-purple pigment in the vacuoles of the mycelium rather than their requirement for adenine, this system is both a morphological and biochemical specific-locus assay. The use of the ad-3 assay system in experiments with different environmental mutagens has provided precise dose-response curves not only for inactivation, but also the overall induction of ad-3 mutations. Genetic characterization of these ad-3 mutations by a series of 3 rapid and simple genetic tests permits the identification of 18 subclasses of gene/point mutations, and 12 subclasses of multilocus deletion mutations. These subclasses also include 3 different classes of multiple-locus mutations with separate sites of recessive lethal damage either in the immediately adjacent regions or elsewhere in the genome. In summary, this specific-locus assay provides a capability that is unique among eukaryotic organisms for the recovery and analysis of genetic damage at 2 closely linked loci.
authors.affiliation: Center for Life Sciences and Toxicology, Research Triangle Institute, Research Triangle Park, North Carolina 27709.
authors.forename: F J
authors.initials: FJ
authors.lastname: de Serres
mesh_terms: D000225:Adenine / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D004252:DNA Mutational Analysis / Q000379:methods*; D004260:DNA Repair; D004271:DNA, Fungal / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004785:Environmental Pollutants / Q000633:toxicity; D005800:Genes, Fungal / Q000187:drug effects; D005816:Genetic Complementation Test / Q000379:methods*; D008040:Genetic Linkage; D005838:Genotype; D006801:Humans; D008957:Models, Genetic; D016297:Mutagenesis, Site-Directed; D009152:Mutagenicity Tests / Q000379:methods*; D009492:Neurospora crassa / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D017354:Point Mutation; D012307:Risk Factors; D017384:Sequence Deletion; D013268:Stimulation, Chemical
chemical_list: D004271:DNA, Fungal; D004785:Environmental Pollutants; D002245:Carbon Dioxide; D000225:Adenine