Thyroid hormone induces DNA demethylation in Xenopus tadpole brain

Thyroid hormone (T3) plays pivotal roles in vertebrate development, acting via nuclear receptors (TRs) that regulate gene transcription by promoting posttranslational modifications to histones. Methylation of cytosine residues in DNA also modulates gene transcription, and our recent finding of predominant DNA demethylation in the brain of Xenopus tadpoles at metamorphosis, a T3-dependent developmental process, caused us to hypothesize that T3 induces these changes in vivo. Treatment of pre-metamorphic tadpoles with T3 for 24 or 48 hr increased immunoreactivity in several brain regions for the DNA demethylation intermediates 5-hydroxymethylcytosine (5-hmC) and 5-carboxylcytosine, and the methylcytosine dioxygenase ten-eleven translocation 3 (TET3). Thyroid hormone treatment induced locus-specific DNA demethylation in proximity to known T3 response elements within the DNA methyltransferase 3a and Krüppel-like factor 9 genes, analyzed by 5-hmC immunoprecipitation and methylation sensitive ...

甲状腺激素（Thyroid hormone, T3）在脊椎动物发育过程中发挥关键调控作用，通过核受体（nuclear receptors, TRs）介导发挥功能——后者通过促进组蛋白的翻译后修饰调控基因转录。DNA中胞嘧啶残基的甲基化同样可调控基因转录；我们近期发现，在依赖T3的发育进程——非洲爪蟾蝌蚪变态发育中，其脑部存在显著的DNA去甲基化现象，这促使我们提出假说：T3可在体内诱导此类DNA去甲基化变化。
对变态前爪蟾蝌蚪施以T3处理24或48小时后，多个脑区针对DNA去甲基化中间产物5-羟甲基胞嘧啶（5-hydroxymethylcytosine, 5-hmC）、5-羧基胞嘧啶，以及甲基胞嘧啶双加氧酶十十一易位3（ten-eleven translocation 3, TET3）的免疫反应性均显著增强。
通过5-hmC免疫沉淀及甲基化敏感……分析发现，甲状腺激素处理可在DNA甲基转移酶3a（DNA methyltransferase 3a）与Krüppel样因子9（Krüppel-like factor 9）基因内已知T3应答元件附近诱导位点特异性DNA去甲基化。