Assessment of chemical mutagenicity is essential to protecting human health from genetic disease. Current assays are limited in their ability to provide mechanistic insight into the endogenous and exogenous processes involved in mutagenesis. Duplex Sequencing (DS), a novel error-corrected sequencing technology, overcomes many of the limitations faced by conventional mutagenicity assays. DS could be used to eliminate reliance on standalone reporter assays and provide mechanistic information alongside mutation frequency (MF) data. Furthermore, customizable panels enable assessment of the endogenous genomic features that drive mutagenesis. However, the performance of DS must be thoroughly assessed before it can be routinely implemented for standard testing. The objectives of this study were to demonstrate the potential of DS as a robust in vivo mutagenicity test and to explore its rich data to gain a better understanding of spontaneous and chemically-induced mutagenicity in somatic and germ cells. We used DS to study spontaneous and procarbazine (PRC)-induced mutations in the bone marrow (BM) and germ cells of MutaMouse males across a panel of 20 diverse genomic targets. Mice were exposed to 0, 6.25, 12.5, or 25 mg/kg-bw/day for 28 days by oral gavage and tissues were sampled at least 28 days post-exposure. Results were compared with those obtained using the conventional lacZ viral plaque assay on the same samples. DS detected significant increases in MF and distinct spectra consistent with the known mutagenic mechanisms of PRC in both tissues. Mouse PRC doses at which significant effects were observed are in range with those used for chemotherapy, suggesting that similar effects may be observed in human patients. This supports the contribution of PRC towards secondary cancers following treatment. DS results were comparable to those obtained using the gold-standard lacZ TGR assay, with DS showing greater sensitivity to detect smaller changes in MF. Analysis of mutation spectra and the genomic features that drive the mutational response revealed intrinsic differences between BM and germ cells that may underlie differences in endogenous mutagenic mechanisms and/or DNA repair pathways. The results suggest that germ cells may have intrinsic mechanisms to reduce mutation burden relative to somatic cells. While historically analysis of germ cell mutagenicity has been neglected in favour of somatic cells, our work supports the independent assessment of germ cell mutagenicity during regulatory testing. Finally, we conducted power analyses to inform the optimal DS study designs for the two tissues. We found that low intra-group variability within BM samples allows a reduction in sample size to three animals per group whilst still maintaining 80% power to detect an effect. In contrast, the relatively high intra-group variability and low background MF in germ cells suggests a minimum of eight animals per group to detect an effect. Overall, our results support the use of DS as a mutagenicity test and highlight many of the advantages it holds over conventional assays. Moreover, our study reveals the potential for mutagenic effects in PRC-treated cancer patients. Further work to test DS with more chemicals and across a wider range of tissues is recommended for future implementation as a mutagenicity test.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/45290 |
| Date | 15 August 2023 |
| Creators | Dodge, Annette |
| Contributors | Yauk, Carole, Marchetti, Francesco |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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