Gamma radiation induces locus specific changes to histone modification enrichment in zebrafish and Atlantic salmon

Ionizing radiation is a recognized genotoxic agent, however, little is known about the role of the functional form of DNA in these processes. Post translational modifications on histone proteins control the organization of chromatin and hence control transcriptional responses that ultimately affect the phenotype. The purpose of this study was to investigate effects on chromatin caused by ionizing radiation in fish. Direct exposure of zebrafish (Danio rerio) embryos to gamma radiation (10.9 mGy/h for 3h) induced hyper-enrichment of H3K4me3 at the genes hnf4a, gmnn and vegfab. A similar relative hyper-enrichment was seen at the hnf4a loci of irradiated Atlantic salmon (Salmo salar) embryos (30 mGy/h for 10 days). At the selected genes in ovaries of adult zebrafish irradiated during gametogenesis (8.7 and 53 mGy/h for 27 days), a reduced enrichment of H3K4me3 was observed, which was correlated with reduced levels of histone H3 was observed. F1 embryos of the exposed parents showed hyper-methylation of H3K4me3, H3K9me3 and H3K27me3 on the same three loci, while these differences were almost negligible in F2 embryos. Our results from three selected loci suggest that ionizing radiation can affect chromatin structure and organization, and that these changes can be detected in F1 offspring, but not in subsequent generations.

电离辐射（ionizing radiation）是公认的遗传毒性因子，然而目前对于DNA功能构象在这类过程中所发挥的作用仍知之甚少。组蛋白的翻译后修饰（post translational modifications）可调控染色质（chromatin）的空间组织形式，进而控制转录应答，最终影响生物体表型。本研究旨在探究电离辐射对鱼类染色质造成的影响。将斑马鱼（Danio rerio）胚胎直接暴露于γ射线（gamma radiation）下（剂量率10.9 mGy/h，持续3小时）后，其hnf4a、gmnn与vegfab基因位点的H3K4me3修饰出现显著富集。大西洋鲑（Salmo salar）受照射胚胎的hnf4a基因位点也观察到了类似的相对富集现象，照射条件为30 mGy/h，持续10天。对在配子发生阶段接受照射的成年斑马鱼卵巢中的目标基因进行检测后，发现其H3K4me3修饰富集水平出现下降，且该现象与组蛋白H3的表达量降低存在相关性。亲代受照射个体的F1胚胎在上述三个基因位点上均出现H3K4me3、H3K9me3与H3K27me3的高富集，而F2胚胎中这类差异几乎可以忽略不计。基于三个目标基因位点的研究结果表明，电离辐射可改变染色质的结构与组织形式，且这类改变可在F1子代中检测到，但无法传递至后续世代。