Transcriptional activation of BmToll9-2 to exogenous dsRNA in the larvae of Bombyx mori

Abstract

The Toll pathway plays a crucial role in insect innate immunity, functioning through pattern recognition receptors (PRRs) that detect pathogen associated molecular patterns (PAMPs). Previous studies on BmToll9-2 have primarily investigated its role in sensing bacterial pathogens and activating antimicrobial peptides. In this study, we aimed to investigate the transcriptional regulation of BmToll9-2 in response to exogenous double-stranded RNAs (dsRNAs) in silkworm (Bombyx mori) larvae. Various delivery routes for dsRNA-triggered activation of BmToll9-2 were explored. Quantitative real-time PCR (qRT-PCR) assays revealed significant up-regulation of BmToll9-2 in the midgut, fat body, and epidermis following dsRNA injection. In contrast, oral administration of dsRNA failed to induce a transcriptional response. In vitro stability assays demonstrated that dsRNA was rapidly degraded in midgut fluid (within 10 min) but remains stable in the hemolymph for an extended period (up to 6 h). In vivo detection of dsRNA further confirmed its rapid digestion through feeding and the longer retention through injection. Additionally, infection with B. mori cytoplasmic polyhedrosis virus (BmCPV) also induced BmToll9-2 expression, suggesting a link between dsRNA viruses and Toll pathway activation. Our findings suggest dsRNAs as potential PAMPs for Toll receptor signaling, highlighting the longer persistence of dsRNA in the hemolymph as a significant factor in the transcriptional response and emphasizing the role of BmToll9-2.