公益財団法人 セコム科学技術振興財団
研究成果報告書

研究課題名
生活習慣病による生殖細胞のエピジェネティック変化およびゲノム変異の発生機序
Mechanisms for Epigenetic and genetic alterations in male germ cells by lifestyle diseases

研究期間
平成 29 年 10 月 ～ 令和 4 年 3 月

報告年月
令和 4 年 8 月

名古屋大学

研究代表者
大学院生命農学研究科
一柳 健司

動物科学専攻教授

Kenji Ichiyanagi
Professor, Department of Animal Sciences,
Graduate School of Bioagricultural Sciences, Nagoya University

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Abstract
Epigenetics is a phenomenon and mechanism, in which and by which altered phenotypes aremaintained without a change in the DNA sequence. Epigenetics, involving a long-term
regulation of gene expression, are regulated by DNA methylation, histone modifications andsmall RNAs. For example, when DNA in promoter regions becomes methylated, the gene
expression becomes shut off. Epigenome is a term to explain the entire epigenetic information
in a cell.
In the case of mammals, epigenetic phenomena are observed within an individual but not
between parents and their offspring. Recently, however, studies in humans and mice havereported that lifestyle-related diseases, such as diabetes, of a parent can increases the risk ofthe disease in the offspring. A possible explanation for this inter-generational transmission isthat lifestyle-related diseases change the methylation pattern of gametes' DNA and thosechanges are inherited. However, it is known that the methylation state of sperm DNA is largely
erased after fertilization. Therefore, the "epigenetic inheritance hypothesis of lifestyle-relateddiseases" remains under hot debate.
In this study, using deep sequencing, we studied epigenomic abnormalities in sperm due todiabetes and their heritability in a mouse model. By taking advantage of our establishedmethod to purify different stages of male germ cells by FACS, we aimed to clarify at what stageof development epigenetic abnormalities emerge. On the other hand, we also analyzed theoffspring of diabetic fathers to elucidate the molecular mechanisms of epigenetic inheritance.
To this end, a group of mice were treated with a beta-cell-killing agent serving as the diabeticmodel, while the other group of mice were untreated.
Our results showed that, in the parental germ cells, no major changes were observed at thelevel of gene expression, but DNA methylation was altered in thousands of genomic regions.
Inspection of these sequences revealed the enrichment of several transcription-factor-binding
motifs, including that of ZFP57. Next, we studied their offspring. We found that offspring of
diabetic fathers showed an abnormal response to insulin. Then, we determined thetranscriptomes and DNA methylomes of their islets and liver. We found decreased expression of
the insulin genes in the islets and increased expression of gluconeogenesis-related genes in theliver of the offspring of diabetic fathers. In addition, DNA methylation differences were againobserved in thousands of genomic regions in the islets and liver, respectively. Although many ofthese are not promoters of differentially expressed genes, many DNA methylation changes
occurred in known enhancer regions, which may therefore alter the expression of genes.
Importantly, some of the DNA methylation differences seen in the parental sperm were also
seen in the offspring organs. The sequences in these regions were enriched with the ZFP57
binding motif. These results suggest that the abnormal DNA methylation that occurred insperm is protected by ZFP57 from extensive reprogramming, and thus transmitted to theoffspring. Future studies, including DNA methylation analysis in early embryos and histone
modification analysis, will hopefully reveal the nature of epigenetic inheritance in mammals.

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