Dnmt1a is essential for gene body methylation and the regulation of the zygotic genome in a wasp.
Dnmt1a is essential for gene body methylation and the regulation of the zygotic genome in a wasp.
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DOI：
10.1371/journal.pgen.1010181
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发表时间：
2022-05
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影响因子：
4.5
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基因体甲基化（Gene body methylation，GBM）是DNA甲基化的一种祖先模式，其在发育中的作用被启动子和CpG岛甲基化所掩盖。丽蝇蛹集蜂的启动子和CpG岛甲基化很少，但保留了强大的GBM，使其成为阐明GBM作用的极好模型。在这里，我们证明了N。丽翅虫DNA甲基转移酶1a（Nv-Dnmt 1a）敲低导致胚胎细胞化和原肠胚形成失败。这两个被破坏的事件都是昆虫的母合子转换（MZT）的标志。对胚胎转录组和甲基化组的分析显示，Nv-Dnmt 1a敲低后，GBM强烈减少，胚胎发生期间基因表达广泛中断。引人注目的是，在数千个甲基化位点中，GBM的丢失和基因表达降低之间存在强烈的相关性，这与GBM直接促进高水平转录的假设一致。我们认为，由于GBM减少而导致的甲基化基因表达水平降低是Nv-Dnmt 1敲低的关键直接效应。随后，甲基化基因的破坏导致MZT的下游失调，最终导致原肠胚形成时的发育失败。合子基因组在发育的早期阶段的适当激活和调节是昆虫在早期有丝分裂后进行发育所必需的。我们已经发现，这一过程是深刻的DNA甲基转移酶基因（Nv-Dnmt 1a）在黄蜂Nasonia vitripennis减少后中断，导致细胞化和形态发生运动的失败。与其他昆虫一样，DNA甲基化几乎只发生在Nasonia基因体中，并且这种甲基化在Nv-dnmt 1敲低后强烈降低。来自甲基化基因的表达水平也降低，与甲基化损失的程度成比例。这些结果指出了基因体甲基化在调节与重要发育事件相关的基因表达水平中的关键作用。这与其他昆虫的研究不同，可能表明昆虫中基因体甲基化和Dnmt 1直系同源物的作用多样性。
Gene body methylation (GBM) is an ancestral mode of DNA methylation whose role in development has been obscured by the more prominent roles of promoter and CpG island methylation. The wasp Nasonia vitripennis has little promoter and CpG island methylation, yet retains strong GBM, making it an excellent model for elucidating the roles of GBM. Here we show that N. vitripennis DNA methyltransferase 1a (Nv-Dnmt1a) knockdown leads to failures in cellularization and gastrulation of the embryo. Both of these disrupted events are hallmarks of the maternal-zygotic transition (MZT) in insects. Analysis of the embryonic transcriptome and methylome revealed strong reduction of GBM and widespread disruption of gene expression during embryogenesis after Nv-Dnmt1a knockdown. Strikingly, there was a strong correlation between loss of GBM and reduced gene expression in thousands of methylated loci, consistent with the hypothesis that GBM directly facilitates high levels of transcription. We propose that lower expression levels of methylated genes due to reduced GBM is the crucial direct effect of Nv-Dnmt1 knockdown. Subsequently, the disruption of methylated genes leads to downstream dysregulation of the MZT, culminating in developmental failure at gastrulation. The proper activation and regulation of the zygotic genome in the early stages of development is required for development to proceed past early mitotic divisions in insects. We have found that this process is profoundly disrupted after reduction of a DNA methyltransferase gene (Nv-Dnmt1a) in the wasp Nasonia vitripennis, resulting in failure of cellularization and morphogenetic movements. Like other insects, DNA methylation occurs almost exclusively in Nasonia gene bodies, and this methylation is strongly reduced after Nv-dnmt1 knockdown. Expression levels from methylated genes are also reduced, in proportion to the degree of methylation loss. These results point to a key role of gene body methylation in regulating gene expression levels that are relevant to important developmental events. This differs from studies in other insects, potentially indicating a diversity of roles of gene body methylation and Dnmt1 orthologs among the insects.