The effects of in utero irradiation on mutation induction and transgenerational instability in mice

Abstract

It is well known that the developing embryo is especially sensitive to ionising radiation. However, to date little is known about the long-term effects of in utero exposure on mutation rates during adulthood. To evaluate the effects of in utero irradiation on mutation induction and transgenerational instability, BALB/c pregnant mice (Theiler stage 20, 12 days of gestation) were exposed to 1 Gy of acute X-rays. The in utero exposed 8-week-old males and females were mated to control partners. To evaluate the effects of in utero irradiation on mutation induction in the germline of exposed mice, all parents and offspring were profiled using two mouse-specific expanded simple tandem repeat (ESTR) probes Ms6-hm and Hm-2. The results of our study show that ESTR mutation rates in the germline of in utero irradiated male and female mice remain highly elevated during adulthood. Using single-molecule PCR, the frequency of ESTR mutation was established in DNA samples prepared from sperm, bone marrow and brain taken from the in utero irradiated animals. In all animals, a statistically significant ∼2.8-3.7 fold increase in the mean mutation frequency was found in all tissues of the in utero irradiated animals. The results of our study show that the mutagenic effects of in utero irradiation in mice are well manifested during adulthood and therefore suggest that the susceptibility of early stages of mouse development to ionising radiation may be higher than previously thought. To analyse the effects of parental irradiation on transgenerational instability, the frequency of ESTR mutation was established in DNA samples prepared from sperm, bone marrow and brain taken from the first-generation offspring of in utero irradiated male and female mice. The results of our study show that in the offspring of in utero exposed males the frequency of ESTR mutation is considerably elevated across multiple tissues, whereas in the offspring of irradiated females it does not significantly differ from that in controls. A comparison with the results of our previous studies on transgenerational in stability among the offspring of BALB/c male mice irradiated during adulthood showed that that the magnitude of transgenerational effects is not affected by the stage of paternal exposure. This work has therefore established that an instability signal induced in the germline of in utero irradiated males is manifested during adulthood. The potential implications of our findings to for further understanding of the possible mechanisms of transgenerational genomic instability will be discussed.

Exposure to anticancer drugs can result in transgenerational genomic instability in mice

“…These data are in line with the results of previous studies on the transgenerational effects of paternal irradiation showing significantly increased ESTR mutation frequencies in the germline and somatic tissues in the offspring of irradiated male mice (8,9,24); the same tissue-wide destabilization of the F 1 genome has been demonstrated in the present study. Moreover, other recent studies have shown a similarly elevated mutation rate in the offspring of irradiated male mice at the alleles derived from exposed and nonexposed parents (7,8,25); the same holds for the offspring of anticancer drug-treated males.…”

“…Finally, according to the results of our previous studies, transgenerational instability in the offspring of irradiated male mice is an epigenetic phenomenon (7)(8)(9)). This conclusion is based mainly on the fact that vast majority of the F 1 offspring show similar levels of instability in numerous tissues (8).…”

“…Recent mouse studies have shown that the genetic effects of exposure to ionizing radiation and some chemical mutagens might not be restricted to the directly affected parental germ line, but also can manifest in their offspring (6)(7)(8)(9)(10). One of the key aspects of transgenerational effects is destabilization of the offspring's genomes, detectable across at least two generations.…”

Direct and delayed X‐ray‐induced DNA damage in male mouse germ cells

“…This phenomenon has also been observed in male germ cells [de Boer et al, 2010]. Spermatogonial irradiation causes delayed genomic instability in descendant sperm [Sailer et al, 1995;Haines et al, 2001Haines et al, , 2002Cordelli et al, 2003] as well as in the progeny of irradiated male parents in rodents [Baulch and Raabe, 2005;Barber and Dubrova, 2006;Barber et al, 2009] and humans [Aghajanyan et al, 2011]. Remodeling of chromatin domains and nuclear matrix during spermiogenesis and in the zygote has been suggested to play a role in these phenomena [de Boer et al, 2010], but how and when they operate is still unclear.…”

The effects of methyl-donor deficiency on mutation induction and transgenerational instability in mice

“…When tissues from the offspring of the directly irradiated animals were investigated, it was revealed that in contrast to paternal irradiation, maternal exposure did not affect the genomic stability of their offspring. It is possible that even though the epigenetic marks of foetal irradiation can survive developmental reprogramming in both males and females, and lead to genomic instability during adulthood, the failure of irradiated females to pass an instability signal to their offspring to be associated with early postfertilisation events (Barber et al, 2009). …”