Tandem repeat DNA: applications in mutation analysis

Abstract

Non-coding tandem repeat DNA sequences have high rates of mutation that facilitate the measurement of induced mutation in small sample sizes. It has been suggested that these loci may be useful biomarkers for heritable genetic mutation induced by exposure to genotoxic agents. Significant induction of mutation is quantifiable in the germline of mice exposed to mutagens. The primary focus of this work has been on exposure to radiation. The data suggest that meiosis or DNA replication/repair may be required for induction of mutation in the germline at tandem repeats. Mutations arise via indirect mechanisms rather than by direct damage to the repeat locus itself, therefore reflecting genomic instability rather than targeted DNA damage. These markers have also been used to measure induced germline mutations in animals exposed to ambient levels of urban air pollution. The mutagenicity is associated with particulate matter in the air but the exact chemical nature of the mutagens is unknown. Lack of knowledge of the relationship between ESTR instability and gene mutation, and lack of understanding of the mechanisms resulting in instability prevent inference on the health-related implications of induced tandem repeat mutation. We have developed single-molecule PCR approaches to study ESTR instability in vitro. This method circumvents the requirement of sub-cloning and allows for many more individual ESTR alleles to be examined. These types of laboratory-based experiments will be crucial in clarifying the types of chemicals that can generate tandem repeat instability and thereby provide insight into the mechanisms of action and the putative mutagens found in complex environmental matrices.