The high abundance of chemical pollutants in the environment represents a genetic risk to humans. The development of reliable and sensitive tests for the analysis of the genetic effects of exposure to chemical mutagens is required. Previous work has shown that expanded simple tandem repeat (ESTR) loci provide a sensitive system for monitoring radiation-induced mutation in the mouse germline.\ud Here, the results of the first systematic study on germline mutation induction at mouse ESTR loci by chemical mutagens are presented. Mutation rates at two ESTR loci were studied in the germline of male mice exposed to two monofunctional alkylating agents, ethyl-nitrosourea (ENU) and isopropyl methanesulfonate (iPMS), as well as to the topoisomerase-II inhibitor, etoposide (ET). Pre-meiotic exposure to alkylating agents resulted in a highly significant increase in ESTR mutation rate, but did not alter post-meiotically exposed cells. Pre-meiotic mutation induction by ENU and iPMS was linear within the interval of doses from 12.5 mg/kg to 25 mg/kg and reached a plateau at higher concentrations. Paternal exposure to etoposide resulted in ESTR mutation induction at meiotic stages but did not affect post- or pre-meiotic cells. The pattern of ESTR mutation induction after pre-meiotic and meiotic exposure to chemical mutagens was similar to that previously obtained by various traditional approaches for monitoring germline mutation in mice.\ud Using microarrays, the analysis of the pattern of changes in gene expression in the testis of male mice exposed to ENU was studied. This analysis revealed that exposure to this chemical mutagen does not result in detectable changes in gene expression.\ud The results of this study show that ESTR loci provide a new and efficient biomonitoring system for assessing the genetic effects of chemical mutagens, capable of detecting increases in mutation rates at very low doses and in small sample sizes
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