Knockdown of Dnmt1 links Gene body DNA methylation to regulation of gene expression and maternal-zygotic transition in the wasp Nasonia
AbstractGene body methylation (GBM) is an ancestral form of DNA methylation whose role in development has remained unclear. Unlike vertebrates, DNA methylation is found exclusively in gene bodies in the wasp Nasonia vitripennis, which provides a unique opportunity to interpret the role of GBM in development. We confirmed that parental RNAi (pRNAi) knockdown of a DNMT1 ortholog (Nv-Dnmt1a) in Nasonia leads to embryonic lethality and failures in cellularization and morphogenesis. Using whole-genome bisulfite sequencing, we found a widespread loss of GBM in Nv-Dnmt1a pRNAi embryos. Using RNAseq, we found that methylated genes that lost GBM in the pRNAi samples were exclusively downregulated during zygotic genome activation. Unexpectedly, nearly all affected unmethylated genes were up-regulated after pRNAi. Lack of proper clearance of mRNAs and abnormal activation drive this up-regulation, indicating critical roles for Nv-Dnmt1a and GBM in the maternal-zygotic transition (MZT) in the wasp, despite their absence in Drosophila.