Data from: Methylation of avpr1a in the cortex of wild prairie voles: Effects of CpG position and polymorphism

DNA methylation can cause stable changes in neuronal gene expression, but we know little about its role in individual differences in the wild. In this study we focus on the vasopressin 1a receptor (avpr1a), a gene extensively implicated in vertebrate social behavior, and explore natural variation in DNA methylation, genetic polymorphism and neuronal gene expression among 30 wild prairie voles (Microtus ochrogaster). Examination of CpG density across 8kb of the locus revealed two distinct CpG islands overlapping promoter and first exon, characterized by few CpG polymorphisms. We used a targeted bisulfite sequencing (bis-seq) approach to measure DNA methylation across ~3kb of avpr1a in the retrosplenial cortex, a brain region implicated in male space use and sexual fidelity. We find dramatic variation in methylation across the avrp1a locus, with pronounced diversity near the exon-intron boundary and in a genetically variable putative enhancer within the intron. Among our wild voles, differences in cortical avpr1a expression correlate with DNA methylation in this putative enhancer, but not with the methylation status of the promoter. We also find an unusually high number of polymorphic CpG sites (polyCpGs) in this focal enhancer. One polyCpG within this enhancer (polyCpG 2170) may drive variation in expression either by disrupting transcription factor binding motifs or by changing local DNA methylation and chromatin silencing. Our results contradict some assumptions made within behavioral epigenetics, but are remarkably concordant with genome-wide studies of gene regulation.DNA甲基化（DNA methylation）可引发神经元基因表达的稳定改变，但目前学界对其在野外个体差异中的作用仍知之甚少。本研究聚焦于加压素1a受体（vasopressin 1a receptor，简称avpr1a）——一种广泛参与脊椎动物社会行为的功能基因，并针对30只野生草原田鼠（Microtus ochrogaster），探究其DNA甲基化、遗传多态性与神经元基因表达的自然变异模式。对该基因座8kb区段的CpG密度分析显示，存在两个独立的CpG岛（CpG island），分别覆盖启动子与第一外显子区域，且该区域内CpG多态性位点较为稀缺。本研究采用靶向亚硫酸氢盐测序（bisulfite sequencing，简称bis-seq）技术，对 retrosplenial皮层（retrosplenial cortex，该脑区与雄性空间利用及配偶忠诚行为密切相关）中约3kb的avpr1a区段的DNA甲基化水平进行定量检测。研究结果表明，avpr1a基因座的甲基化水平存在显著变异，在外显子-内含子边界及内含子内一个携带遗传变异的推定增强子（putative enhancer）区域，甲基化多样性尤为突出。在本次研究的野生田鼠群体中，皮层avpr1a的表达差异与该推定增强子区域的DNA甲基化水平呈显著相关，但与启动子区域的甲基化状态并无关联。此外，我们在该焦点增强子区域发现了异常大量的多态性CpG位点（polymorphic CpG sites，简称polyCpGs）。其中，该增强子内的一个多态性CpG位点（polyCpG 2170）可能通过两种方式介导基因表达变异：一是破坏转录因子结合基序（transcription factor binding motif），二是改变局部DNA甲基化水平与染色质沉默（chromatin silencing）状态。本研究结论与行为表观遗传学（behavioral epigenetics）领域的部分既有假设相悖，但与基因调控相关的全基因组研究（genome-wide study）结果高度吻合。