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Methyl‐CpG (mCpG) binding domain (MBD) proteins especially bind with methylated DNA, and are involved in many important biological processes; however, the binding mechanism between insect MBD2/3 and mCpG remains unclear. In this study, we identified 2 isoforms of the MBD2/3 gene in Bombyx mori, MBD2/3‐S and MBD2/3‐L. Binding analysis of MBD2/3‐L, MBD2/3‐S, and 7 mutant MBD2/3‐L proteins deficient in β1−β6 or α1 in the MBD showed that β2−β3‐turns in the β‐sheet of the MBD are necessary for the formation of the MBD2/3–mCpG complex; furthermore, other secondary structures, namely, β4−β6 and an α‐helix, play a role in stabilizing the β‐sheet structure to ensure that the MBD is able to bind mCpG. In addition, sequence alignment and binding analyses of different insect MBD2/3s indicated that insect MBD2/3s have an intact and conserved MBD that binds to the mCpG of target genes. Furthermore, MBD2/3 RNA interference results showed that MBD2/3‐L plays a role in regulating B. mori embryonic development, similar to that of DNA methylation; however, MBD2/3‐S without β4−β6 and α‐helix does not alter embryonic development. These results suggest that MBD2/3‐L recognizes and binds to mCpG through the intact β‐sheet structure in its MBD, thus ensuring silkworm embryonic development. [ABSTRACT FROM AUTHOR]

Spodoptera litura is a destructive agricultural pest in tropical and subtropical areas. Understanding the molecular mechanisms of S. litura adaptation to its preferred host plants may help identify target genes useful for pest control. We used high‐throughput sequencing to characterize the expression patterns of messenger RNAs (mRNAs) and microRNAs (miRNAs) in the midgut of S. litura fed on Brassica juncea for 6 h and 48 h. A total of 108 known and 134 novel miRNAs were identified, 29 miRNAs and 237 mRNAs were differentially expressed at 6 h of B. juncea feeding, 26 miRNAs and 433 mRNAs were differentially expressed at 48 h. For the mRNAs, the up‐regulated genes were mostly enriched in detoxification enzymes (cytochrome P450, esterase, glutathione S‐transferase, uridine diphosphate‐glucuronosyl transferase), while the down‐regulated genes were mostly enriched in proteinases and immune‐related genes. Furthermore, most detoxification enzymes begin to up‐regulate at 6 h, while most digestion and immune‐related genes begin to up‐ or down‐regulate at 48 h. Eighteen and 37 differently expressed transcription factors were identified at 6 h and 48 h, which may regulate the functional genes. We acquired 136 and 41 miRNA versus mRNA pairs at 6 h and 48 h, respectively. Some down‐regulated and up‐regulated miRNAs were predicted to target detoxification enzymes and proteinases, respectively. Real‐time quantitative polymerase chain reaction of nine randomly selected miRNAs and 28 genes confirmed the results of RNA‐seq. This analyses of miRNA and mRNA transcriptomes provides useful information about the molecular mechanisms of S. litura response to B. juncea. [ABSTRACT FROM AUTHOR]

Cell division and differentiation after egg fertilization are critical steps in the development of embryos from single cells to multicellular individuals and are regulated by DNA methylation via its effects on gene expression. However, the mechanisms by which DNA methylation regulates these processes in insects remain unclear. Here, we studied the impacts of DNA methylation on early embryonic development in Bombyx mori . Genome methylation and transcriptome analysis of early embryos showed that DNA methylation events mainly occurred in the 5' region of protein metabolism-related genes. The transcription factor gene zinc finger protein 615 ( ZnF615 ) was methylated by DNA methyltransferase 1 (Dnmt1) to be up-regulated and bind to protein metabolism-related genes. Dnmt1 RNA interference (RNAi) revealed that DNA methylation mainly regulated the expression of nonmethylated nutrient metabolism-related genes through ZnF615 . The same sites in the ZnF615 gene were methylated in ovaries and embryos. Knockout of ZnF615 using CRISPR/Cas9 gene editing decreased the hatching rate and egg number to levels similar to that of Dnmt1 knockout. Analysis of the ZnF615 methylation rate revealed that the DNA methylation pattern in the parent ovary was maintained and doubled in the offspring embryo. Thus, Dnmt1-mediated intragenic DNA methylation of the transcription factor ZnF615 enhances its expression to ensure ovarian and embryonic development.