Data from: Genetic variation in the developmental regulation of cortical avpr1a among prairie voles

Early experiences can have enduring impacts on brain and behavior, but the strength of these effects can be influenced by genetic variation. In principle, polymorphic CpGs (polyCpGs) may contribute to gene-by-environment interactions (GxE) by altering DNA methylation. In this study, we investigate the influence of polyCpGs on the development of vasopressin receptor 1a abundance in the retrosplenial cortex (RSC-V1aR) of prairie voles (Microtus ochrogaster). Two alternative alleles (HI/LO) predict RSC avpr1a expression, V1aR abundance and sexual fidelity in adulthood; these alleles differ in the frequency of CpG sites and in methylation at a putative intron enhancer. We hypothesized that the elevated CpG abundance in LO alleles would make homozygous LO/LO voles more sensitive to developmental perturbations. We found that genotype differences in RSC-V1aR abundance emerged early in ontogeny and were accompanied by differences in methylation of the putative enhancer. As predicted, postnatal treatment with an oxytocin receptor antagonist (OTA) reduced RSC-V1aR abundance in LO/LO adults but not their HI/HI siblings. Similarly, methylation inhibition by zebularine increased RSC-V1aR in LO/LO adults, but not in HI/HI siblings. These data demonstrate a gene-by-environment interaction in RSC-V1aR. Surprisingly, however, neither OTA nor zebularine altered adult methylation of the intronic enhancer, suggesting that differences in sensitivity could not be explained by CpG density at the enhancer alone. Methylated DNA immunoprecipiation-sequencing (MeDIP-seq) revealed additional differentially methylated regions between HI/HI and LO/LO voles. Future research should examine the role of these regions and other regulatory elements in the ontogeny of RSC-V1aR and its developmentally induced changes.

早期经历可对大脑发育与行为模式产生持久影响，而此类效应的强弱程度会受到遗传变异的调控。从理论层面而言，多态性CpG位点（polymorphic CpGs，简称polyCpGs）可通过改变DNA甲基化水平，参与基因-环境交互作用（gene-by-environment interactions, GxE）。本研究针对多态性CpG位点对草原田鼠（Microtus ochrogaster）后扣带回皮层（retrosplenial cortex，简称RSC）内加压素1a受体（vasopressin receptor 1a, V1aR）丰度发育的影响展开探究。
两种等位基因（高丰度型HI/低丰度型LO）可预测成年个体RSC内精氨酸加压素1a受体基因（avpr1a）的表达水平、V1aR丰度及性忠诚度；两类等位基因在CpG位点的数量以及推定内含子增强子的甲基化水平上均存在差异。我们提出假说：低丰度型等位基因（LO）中更高的CpG丰度，会使纯合子LO/LO型田鼠对发育扰动更为敏感。
研究结果显示，RSC-V1aR丰度的基因型差异在发育早期便已显现，并伴随推定增强子甲基化水平的差异。正如预测所示，产后给予催产素受体拮抗剂（oxytocin receptor antagonist, OTA）可降低LO/LO型成年个体的RSC-V1aR丰度，但对其HI/HI型同胞个体无此效应。同理，通过泽布拉林（zebularine）抑制甲基化可提升LO/LO型成年个体的RSC-V1aR水平，却不会改变HI/HI型个体的对应指标。上述数据证实了RSC-V1aR存在基因-环境交互作用。
但令人意外的是，无论是OTA还是泽布拉林均未改变该内含子增强子的成年期甲基化水平，这表明敏感性差异无法仅通过增强子区域的CpG密度来解释。甲基化DNA免疫沉淀测序（methylated DNA immunoprecipitation-sequencing, MeDIP-seq）结果显示，HI/HI与LO/LO型田鼠之间还存在其他差异甲基化区域。未来的研究应深入探究这些区域及其他调控元件在RSC-V1aR发育过程及其诱导性变化中的作用。