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Ionizing radiation induces transgenerational effects of DNA methylation in zebrafish

ABSTRACT: Ionizing radiation is known to cause DNA damage, yet the mechanisms underlying potential transgenerational effects of exposure have been scarcely studied. Previously, we observed effects in offspring of zebrafish exposed to gamma radiation during gametogenesis. Here, we hypothesize that these effects are accompanied by changes of DNA methylation possibly inherited by subsequent generations. We assessed DNA methylation in F1 embryos (5.5 hours post fertilization) with whole genome bisulfite sequencing following parental exposure to 8.7 mGy/h for 27 days and found 5658 differentially methylated regions (DMRs). DMRs were predominantly located at known regulatory regions, such as gene promoters and enhancers. Pathway analysis indicated the involvement of DMRs related to similar pathways found with gene expression analysis, such as development, apoptosis and cancers, which could be linked to previous observed developmental defects and genomic instability in the offspring. Follow up of 19 F1 DMRs in F2 and F3 embryos revealed persistent effects up to the F3 generation at 5 regions. These results indicate that ionizing radiation related effects in offspring can be linked to DNA methylation changes that partly can persist over generations. Monitoring DNA methylation could serve as a biomarker to provide an indication of ancestral exposures to ionizing radiation.

ORGANISM(S): Danio rerio

PROVIDER: GSE100470 | GEO | 2017/12/08

SECONDARY ACCESSION(S): PRJNA391914

REPOSITORIES: GEO

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Project description:Background: DNA methylation (DNAme) erasure and reacquisition occurs during prenatal male germ cell development; some further remodelling takes place after birth during spermatogenesis. Environmental insults during germline epigenetic reprogramming may affect DNAme, presenting a potential mechanism for transmission of environmental exposures across multiple generations. Objectives: We investigated how germ cell DNAme is impacted by lifetime exposures to diets containing either low or high, clinically relevant, levels of the methyl donor folic acid and whether resulting DNAme alterations were inherited in germ cells of male offspring of subsequent generations. Materials and Methods: Female mice were placed on a 7-fold folic acid deficient (7FD) and 10- or 20-fold supplemented (10FS and 20FS) diets before and during pregnancy. Resulting F1 litters were weaned on the respective diets. F2 and F3 males received control diets. Genome-wide DNAme was assessed in F1 spermatogonia, and in F1, F2 and F3 sperm. Results: In F1 germ cells, a greater number of differentially methylated cytosines (DMCs) was observed in spermatogonia as compared with F1 sperm for all folic acid diets. DMCs were lower in number in F2 versus F1 sperm, while an unexpected increase was found in F3 sperm. DMCs were predominantly hypomethylated, with genes in neurodevelopmental pathways commonly affected in F1, F2 and F3 male germ cells. While no DMCs were found to be inherited inter- or transgenerationally, we observed over-representation of repetitive elements, particularly young LINEs. Discussion and Conclusion: These results suggest that the prenatal window is the time most susceptible to folate-induced alterations in sperm DNAme in male germ cells. Altered methylation of specific sites in F1 sperm was not present in later generations. However, the finding of hypomethylated young LINE1 elements in sperm from F1 to F3 males provides insight into potential mechanisms of epigenetic inheritance of the effects of folate deficiency and supplementation.

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Ionizing radiation induces transgenerational effects of DNA methylation in zebrafish

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