8-oxoguanine causes spontaneous de novo germline mutations in mice

Abstract

Spontaneous germline mutations generate genetic diversity in populations of sexually reproductive organisms, and are thus regarded as a driving force of evolution. However, the cause and mechanism remain unclear. 8-oxoguanine (8-oxoG) is a candidate molecule that causes germline mutations, because it makes DNA more prone to mutation and is constantly generated by reactive oxygen species in vivo. We show here that endogenous 8-oxoG caused de novo spontaneous and heritable G to T mutations in mice, which occurred at different stages in the germ cell lineage and were distributed throughout the chromosomes. Using exome analyses covering 40.9 Mb of mouse transcribed regions, we found increased frequencies of G to T mutations at a rate of 2 × 10−7 mutations/base/generation in offspring of Mth1/Ogg1/Mutyh triple knockout (TOY-KO) mice, which accumulate 8-oxoG in the nuclear DNA of gonadal cells. The roles of MTH1, OGG1, and MUTYH are specific for the prevention of 8-oxoG-induced mutation, and 99% of the mutations observed in TOY-KO mice were G to T transversions caused by 8-oxoG; therefore, we concluded that 8-oxoG is a causative molecule for spontaneous and inheritable mutations of the germ lineage cells.

Germline mutation rates and the long-term phenotypic effects of mutation accumulation in wild-type laboratory mice and mutator mice

“…These findings suggest that the mutation rate of the mutator mice was close to the upper limit for the practical maintenance of an inbred laboratory mouse population by natural full-sib mating. This value is supported by the finding that TOY-KO mice, which lack three genes involved in repairing oxidative DNA damage and preventing mutations, have a base-substitution mutation rate that is approximately twice that of the Pold1 exo/exo mice (Table 2) and become extinct within eight generations due to progressively decreasing fitness (Ohno et al 2014). On the other hand, cell population analysis suggested that a 10,000-fold increase in the mutation rate is the upper limit for cell proliferation in diploid yeast and, presumably, in mouse cells (Herr et al 2011(Herr et al , 2014.…”

Fertilization stimulates 8-hydroxy-2′-deoxyguanosine repair and antioxidant activity to prevent mutagenesis in the embryo

“…at the early stages of zygote development prior to the initiation of mitosis in order to prevent irreversible changes in genetic integrity including transversion mutations (Wood et al, 1992;Bruner et al, 2000;Ohno et al, 2014). As such, the limited availability of this crucial enzyme, OGG1, is likely a contributor to the vulnerability of early mammalian embryos to oxidative DNA damage (Meseguer et al, 2007).…”

“…In the absence of successful repair of oxidative lesions such as 8-hydroxy-2'-deoxyguanosine (8OHdG), G-C to T-A transversion mutations (Wood et al, 1992) can occur during DNA replication that not only alter the genetic profile of the zygote itself but also every cell generated by the rapid mitotic divisions that characterize embryogenesis. Thus, transversion mutations within the zygote have the propensity to irreversibly alter gene expression profiles and thence the fidelity of normal embryonic development (Bruner et al, 2000;Wu et al, 2013;Ohno et al, 2014). Despite the importance of repairing oxidative DNA damage at this early stage of development, gametes harboring high levels of 8OHdG at the time of fertilization are known to undergo inadequate DNA repair in the zygote, resulting in detrimental effects on the pre-implantation development of the embryo (Takahashi, 2012;Lane et al, 2014) and on fetal growth and development (Chabory et al, 2009;Lane et al, 2014), as well as defects in offspring, including cancer and a significant reduction in lifespan (Ronen and Glickman, 2001;Vinson and Hales, 2002;Aitken et al, 2009).…”

An engineered cell line lacking OGG1 and MUTYH glycosylases implicates the accumulation of genomic 8-oxoguanine as the basis for paraquat mutagenicity

“…In the case of 8OG, BER involves the activity of 8-oxoguanine DNA glycosylase (OGG1) and MutY homolog (MUTYH), enzymes responsible for removing 8OG (when paired with C) and the mismatched adenine across from 8OG (which leads to mutations), respectively [3, 7, 8]. Defects in these glycosylases lead to excessive accumulation of oxidative stress-induced mutations, and an elevated cancer incidence, as shown in several mouse knockout models ( Mutyh −/− Ogg1 −/− ) [3, 6, 9–11]. …”