The RNase III enzyme Dicer1 is essential for larval development in Bombyx mori.

MicroRNAs (miRNAs) are important regulators of nearly all aspects of biological processes in eukaryotes. During the biogenesis of miRNAs, the RNase III enzyme Dicer processes double-strand precursor miRNAs into mature miRNAs and promotes the assembly of RNA-induced silencing complexes (RISCs). Dicer has been reported to participate in a wide range of physiological processes, including development and immunity, in some insect species. However, the physiological roles of Dicer in lepidopterans remain poorly understood. In this study, we investigated the function of Bombyx mori Dicer1. We first performed sequence alignment and found that the sequence of functional domains of Dicer1 are varied among Lepidoptera, Diptera, Coleoptera, Blattaria, and Orthoptera. Using a binary clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9 genome editing approach, we showed that BmDicer1 mutants have arrested development from the 3rd instar into the 4th instar. RNA sequencing analysis indicated that the defects in BmDicer1 mutants are due to dysregulation of genes that encode proteins involved in metabolism, protein degradation, absorption, and renin-angiotensin pathways. Analysis using quantitative real-time polymerase chain reaction showed that mutation of BmDicer1 altered expression of miRNAs and their target genes. Therefore, our study demonstrates the critical roles of BmDicer1 in miRNA biogenesis and larval development in silkworm.