View Program - 63rd Annual Drosophila Research Conference

While DNA methylation is present in most insects, the toolkit has been lost in the lineage leading to Drosophila. Previous experiments in the wasp Nasonia vitripennis showed that the methylation toolkit component DNA methyltransferase 1 (Nv-dnmt1a) plays an important role in early embryogenesis, and we are using this model to understand the ancestral role of DNA methylation in insect embryos, and how it was replaced in species where the toolkit has been lost. We found that embryonic lethality of Nv-dnmt1a knockdown is preceded by scattered failures of blastoderm cellularization, and subsequent failures of morphogenetic movements. Such phenotypes are typical of defects in the maternal-zygotic transition (MZT), indicating that DNA methylation may have a role in regulating this process in the wasp. Using whole genome bisulfite sequencing, we show that knockdown of Nv-dnmt1a leads to strong reduction of gene body methylation throughout the genome. Using RNAseq, we show that ~90% of genes downregulated after Nv-dnmt1a RNAi are methylated (in wild-type embryos). This is not unexpected, as it has been previously shown that insect DNA methylation is associated with efficient transcription (and not repression or imprinting as found in vertebrate models). As development proceeds, more and more non-methylated loci are affected, showing a likely indirect effect of DNA methylation on the regulation of transcripts during the MZT. We propose that moderate disruption of the large number of methylated genes has cascading effects on the MZT that lead to failure of proper maternal clearance and/or zygotic activation of genes in early embryogenesis of Nasonia.

DNA methylation machinery is required for transcriptome regulation and early development in the wasp Nasonia