Division of Epigenetics, DKFZ-ZMBH Alliance, German Cancer Research Center, 69120 Heidelberg, Germany.
Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 21941-902, Brazil.
Sci Rep. 2016 Nov 2;6:36444. doi: 10.1038/srep36444.
Aedes aegypti mosquitoes are important vectors of viral diseases. Mosquito host factors play key roles in virus control and it has been suggested that dengue virus replication is regulated by Dnmt2-mediated DNA methylation. However, recent studies have shown that Dnmt2 is a tRNA methyltransferase and that Dnmt2-dependent methylomes lack defined DNA methylation patterns, thus necessitating a systematic re-evaluation of the mosquito genome methylation status. We have now searched the Ae. aegypti genome for candidate DNA modification enzymes. This failed to reveal any known (cytosine-5) DNA methyltransferases, but identified homologues for the Dnmt2 tRNA methyltransferase, the Mettl4 (adenine-6) DNA methyltransferase, and the Tet DNA demethylase. All genes were expressed at variable levels throughout mosquito development. Mass spectrometry demonstrated that DNA methylation levels were several orders of magnitude below the levels that are usually detected in organisms with DNA methylation-dependent epigenetic regulation. Furthermore, whole-genome bisulfite sequencing failed to reveal any evidence of defined DNA methylation patterns. These results suggest that the Ae. aegypti genome is unmethylated. Interestingly, additional RNA bisulfite sequencing provided first evidence for Dnmt2-mediated tRNA methylation in mosquitoes. These findings have important implications for understanding the mechanism of Dnmt2-dependent virus regulation.
埃及伊蚊是病毒性疾病的重要媒介。蚊子的宿主因素在病毒控制中起着关键作用，有人提出登革热病毒的复制受 Dnmt2 介导的 DNA 甲基化调控。然而，最近的研究表明 Dnmt2 是一种 tRNA 甲基转移酶，并且 Dnmt2 依赖性甲基组缺乏明确的 DNA 甲基化模式，因此有必要对蚊子基因组的甲基化状态进行系统的重新评估。我们现在已经在埃及伊蚊基因组中搜索了候选的 DNA 修饰酶。这并没有揭示任何已知的（胞嘧啶-5）DNA 甲基转移酶，但鉴定了 Dnmt2 tRNA 甲基转移酶、Mettl4（腺嘌呤-6）DNA 甲基转移酶和 Tet DNA 去甲基酶的同源物。所有基因在蚊子发育的不同阶段都有不同程度的表达。质谱分析表明，DNA 甲基化水平比具有 DNA 甲基化依赖性表观遗传调控的生物体中通常检测到的水平低几个数量级。此外，全基因组亚硫酸氢盐测序未能揭示任何明确的 DNA 甲基化模式的证据。这些结果表明，埃及伊蚊基因组未甲基化。有趣的是，额外的 RNA 亚硫酸氢盐测序首次为蚊子中 Dnmt2 介导的 tRNA 甲基化提供了证据。这些发现对理解 Dnmt2 依赖性病毒调控机制具有重要意义。
