bmo-miR-2739 and the novel microRNA miR-167 coordinately regulate the expression of the vitellogenin receptor in Bombyx mori oogenesis

Vitellogenin receptors (VgRs) play crucial roles in oogenesis by mediating endocytosis of vitellogenin and other nutrients in ovipara. We conducted small RNA sequencing and screening with a luciferase reporter system, and found that bmo-miR-2739 and a novel miRNA (novel-miR-167) coordinately regulate the expression of VgR in Bombyx mori (BmVgR). Further analyses suggested that these two miRNAs direct target repression by binding directly to the BmVgR 3' untranslated region. Forced expression of either miRNA using the piggyBac system blocked vitellogenin (Vg) transport and retarded ovariole development. Antagomir silencing of bmo-miR-2739 or novelmiR-167 resulted in increased amounts of BmVgR protein in the ovaries and BmVgR mRNA in the fat body. This evidence, combined with spatiotemporal expression profiles, revealed that these two miRNAs function together to fine-tune the amount of BmVgR protein for ovarian development. Additionally, novel-miR-167 was mainly responsible for the post-transcriptional repression of BmVgR in nonovarian tissues. The results of this study contribute to our understanding of the function of miRNAs during ovarian development of a lepidopteran and suggest a new strategy for controlling insect reproduction.