BmMBNL Knockout Disrupts Molting of Silkworm, Bombyx mori, Through Inhibiting Expressions of Chitin Synthetase and Chitinase

Abstract

Simple Summary Insects rely on molting to replace their old cuticle for growth, a process tightly regulated at the molecular level. However, the role of miRNA processing in this event remains poorly understood. In this study, we investigated the function of Muscleblind-like (MBNL) protein in the silkworm Bombyx mori, which is involved in miRNA biogenesis. We found that BmMBNL is highly expressed in the epidermis and upregulated during molting. CRISPR/Cas9 knockout of BmMBNL caused severe molting defects, reduced body size, and larval lethality, accompanied by decreased ecdysone titers and impaired chitin layer formation. Mechanistically, loss of BmMBNL led to the upregulation of several miRNAs (miR-1, -71, -263, -8-5p, -2a-3p), which suppressed chitinase expression and disrupted normal molting. These findings reveal a novel miRNA-mediated regulatory axis that controls insect molting. Our work not only advances fundamental understanding of insect development but also provides potential targets for pest management and strategies to improve sericulture productivity, thus offering both ecological and economic benefits to society.