Developmental and Thyroid Hormone Regulation of the DNA Methyltransferase 3a Gene in Xenopus Tadpoles
Developmental and Thyroid Hormone Regulation of the DNA Methyltransferase 3a Gene in Xenopus Tadpoles
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DOI：
10.1210/en.2016-1465
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发表时间：
2016-12-01
期刊：
影响因子：
4.8
通讯作者：
Denver, Robert J.
中科院分区：
文献类型：
--
作者：
Kyono, Yasuhiro;Sachs, Laurent M.;Denver, Robert J.
甲状腺激素对脊椎动物的正常发育至关重要。在两栖动物中，T3通过诱导组织特异性基因调控程序来控制变态。T3作用的标志是染色质结构的修饰，这是基因转录变化的基础。我们发现，在非洲爪蟾蝌蚪的大脑中，新生DNA甲基转移酶（DNMT） dnmt3a的mRNA在蜕变过程中与血浆平行增加，而dnmt1则没有增加[T3]。在饲养水中添加T-3后，蝌蚪脑、尾、后肢dnmt3a mRNA表达呈时间依赖性增加。通过分析蝌蚪尾部T3受体（TR）结合的全基因组分析数据，我们确定了dnmt3a位点内的几个假定的T3反应元件（TREs）。通过体外DNA结合、瞬时转染报告基因和染色质免疫沉淀检测，我们鉴定出两个功能性TREs，相对于dnmt3a转录起始位点为-7.1 kb和+5.1 kb。序列比对表明，这些TREs在两种亲缘蛙种（X. laevis和X. tropicalis）之间是保守的，而在羊膜蛙种之间则不保守。我们之前的研究结果表明，该基因在小鼠大脑中直接受到配体TRs的调控，而这两个小鼠TRs在真足哺乳动物中是保守的，而在爪蟾物种中则不保守。因此，尽管dnmt3a的T3调控可能是脊椎动物的一条古老途径，但负责激素调控的基因组位点可能已经分化或在趋同进化中出现。我们假设T-3对dnmt3a的直接调控可能是调节DNA甲基化全局变化的重要机制。
Thyroid hormone is essential for normal development in vertebrates. In amphibians, T3 controls metamorphosis by inducing tissue-specific gene regulation programs. Ahallmark of T3 action is the modification of chromatin structure, which underlies changes in gene transcription. We found that mRNA for the de novo DNA methyltransferase (DNMT) dnmt3a, but not dnmt1, increased in the brain of Xenopus tadpoles during metamorphosis in parallel with plasma [T3]. Addition of T-3 to the rearing water caused a time-dependent increase in dnmt3a mRNA in tadpole brain, tail, and hind limb. By analyzing data from a genome-wide analysis of T3 receptor (TR) binding in tadpole tail, we identified several putative T3 response elements (TREs) within the dnmt3a locus. Using in vitro DNA binding, transient transfection-reporter, and chromatin immunoprecipitation assays for TRs, we identified two functional TREs at -7.1 kb and +5.1 kb relative to the dnmt3a transcription start site. Sequence alignment showed that these TREs are conserved between two related frog species, X. laevis and X. tropicalis, but not with amniotes. Our previous findings showed that this gene is directly regulated by liganded TRs in mouse brain, and whereas the two mouse TREs are conserved among Eutherian mammals, they are not conserved in Xenopus species. Thus, although T3 regulation of dnmt3a may be an ancient pathway in vertebrates, the genomic sites responsible for hormone regulation may have diverged or arisen by convergent evolution. We hypothesize that direct T-3 regulation of dnmt3a may be an important mechanism for modulating global changes in DNA methylation.