Wolbachia uses a host microRNA to regulate transcripts of a methyltransferase, contributing to dengue virus inhibition in Aedes aegypti.

The endosymbiont Wolbachia is common among insects and known for the reproductive manipulations it exerts on hosts as well as inhibition of virus replication in their hosts. Recently, we showed that Wolbachia uses host microRNAs to manipulate host gene expression for its efficient maintenance in the dengue mosquito vector, Aedes aegypti. Cytosine methylation is mediated by a group of proteins called DNA (cytosine-5) methyltransferases, which are structurally and functionally conserved from prokaryotes to eukaryotes. The biological functions of cytosine methylation include host defense, genome stability, gene regulation, developmental promotion of organs, and lifespan regulation. Ae. aegypti has only one DNA methyltransferase gene (AaDnmt2) belonging to the cytosine methyltransferase family 2, which is the most deeply conserved and widely distributed gene among metazoans. Here, we show that in mosquitoes the introduced endosymbiont, Wolbachia, significantly suppresses expression of AaDnmt2, but dengue virus induces expression of AaDnmt2. Interestingly, we found that aae-miR-2940 microRNA, which is exclusively expressed in Wolbachia-infected mosquitoes, down-regulates the expression of AaDnmt2. Reversely, overexpression of AaDnmt2 in mosquito cells led to inhibition of Wolbachia replication, but significantly promoted replication of dengue virus, suggesting a causal link between this Wolbachia manipulation and the blocking of dengue replication in Wolbachia-infected mosquitoes. In addition, our findings provide an explanation for hypomethylation of the genome in Wolbachia-infected Ae. aegypti.