University/British Heart Foundation Centre for Cardiovascular Science, University of Edinburgh, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh, EH16 4TJ, UK.
MRC Computational Genomics Analysis and Training Programme, University of Oxford, MRC WIMM Centre for Computational Biology, The Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headley Way, Oxford, OX3 9DS, UK.
Genome Biol. 2018 Apr 10;19(1):50. doi: 10.1186/s13059-018-1422-4.
Early life exposure to adverse environments affects cardiovascular and metabolic systems in the offspring. These programmed effects are transmissible to a second generation through both male and female lines, suggesting germline transmission. We have previously shown that prenatal overexposure to the synthetic glucocorticoid dexamethasone (Dex) in rats reduces birth weight in the first generation (F1), a phenotype which is transmitted to a second generation (F2), particularly through the male line. We hypothesize that Dex exposure affects developing germ cells, resulting in transmissible alterations in DNA methylation, histone marks and/or small RNA in the male germline.
We profile epigenetic marks in sperm from F1 Sprague Dawley rats expressing a germ cell-specific GFP transgene following Dex or vehicle treatment of the mothers, using methylated DNA immunoprecipitation sequencing, small RNA sequencing and chromatin immunoprecipitation sequencing for H3K4me3, H3K4me1, H3K27me3 and H3K9me3. Although effects on birth weight are transmitted to the F2 generation through the male line, no differences in DNA methylation, histone modifications or small RNA were detected between germ cells and sperm from Dex-exposed animals and controls.
Although the phenotype is transmitted to a second generation, we are unable to detect specific changes in DNA methylation, common histone modifications or small RNA profiles in sperm. Dex exposure is associated with more variable 5mC levels, particularly at non-promoter loci. Although this could be one mechanism contributing to the observed phenotype, other germline epigenetic modifications or non-epigenetic mechanisms may be responsible for the transmission of programmed effects across generations in this model.
生命早期暴露于不良环境会影响后代的心血管和代谢系统。这些编程效应可以通过雄性和雌性两种途径传递给第二代，这表明存在种系传递。我们之前已经表明，在大鼠中产前过度暴露于合成糖皮质激素地塞米松（Dex）会降低第一代（F1）的出生体重，这种表型会传递给第二代（F2），特别是通过雄性途径。我们假设 Dex 暴露会影响发育中的生殖细胞，导致雄性生殖系中可传递的 DNA 甲基化、组蛋白标记和/或小 RNA 改变。
我们使用甲基化 DNA 免疫沉淀测序、小 RNA 测序和 H3K4me3、H3K4me1、H3K27me3 和 H3K9me3 的染色质免疫沉淀测序，在表达 GFP 转基因的 F1 斯普拉格-道利大鼠的精子中描绘了表观遗传标记，这些大鼠的母亲接受了 Dex 或载体处理。尽管出生体重的影响通过雄性途径传递给了 F2 代，但在 Dex 暴露动物和对照组的生殖细胞和精子中，未检测到 DNA 甲基化、组蛋白修饰或小 RNA 的差异。
尽管表型传递到了第二代，但我们无法在精子中检测到特定的 DNA 甲基化、常见组蛋白修饰或小 RNA 谱的变化。Dex 暴露与更高的 5mC 水平相关，特别是在非启动子基因座。尽管这可能是导致观察到的表型的一种机制，但在该模型中，其他种系表观遗传修饰或非表观遗传机制可能负责跨代传递编程效应。
