Gene-regulatory independent functions for insect DNA methylation

The function of cytosine (DNA) methylation in insects remains unknown. Here we provide evidence for the functional role of the maintenance DNA methyltransferase 1 ( Dnmt1 ) in an insect using experimental manipulation. Through RNA interference (RNAi) we successfully post-transcriptionally knocked down Dnmt1 in ovarian tissue of the hemipteran Oncopeltus fasciatus (the large milkweed bug). Individuals depleted for Dnmt1 , and subsequently DNA methylation, failed to reproduce. Eggs were inviable and declined in number, and nuclei structure of follicular epithelium was aberrant. Depletion of DNA methylation did not result in changes in gene or transposable element expression revealing an important function of DNA methylation seemingly not contingent on gene expression. Our work provides direct experimental evidence for a functional role of Dnmt1 and DNA methylation independent of gene expression in insects.