Circular RNA bmo_circ_0000157 facilitates microsporidian proliferation via an miR‐281‐5p‐mediated regulatory axis in <i>Bombyx mori</i>

Microsporidia are unicellular eukaryotic obligate intracellular parasites that primarily infect vertebrates, invertebrates, and some protists. However, our understanding of microsporidian-host interaction mechanisms remains insufficient, especially the mechanisms underlying the noncoding RNA response to microsporidian infection. To systematically explore the characteristics of the host noncoding RNA response to microsporidian infection, we used whole-transcriptome sequencing technology to identify noncoding RNAs in the Bombyx mori midgut at different time points after Nosema bombycis (N. bombycis) infection. We identified 51 novel microRNAs (miRNAs) and 269 novel circular RNAs (circRNAs) in the Bombyx mori midgut and constructed a differentially expressed (DE)-circRNA-miRNA regulatory interaction network. Furthermore, our qRT-PCR screening revealed that bmo_circ_0000157 (circ_0000157) facilitates N. bombycis proliferation. Ultimately, dual-luciferase reporter and cell-level rescue assays confirmed that circ_0000157 functions as a molecular sponge for bmo-miR-281-5p (miR-281-5p), thereby regulating N. bombycis proliferation. Overall, our results indicate that the novel regulatory target circ_0000157 facilitates N. bombycis proliferation by modulating miR-281-5p expression, thereby altering its effects on downstream target genes. This study expands our understanding of circRNA biological functions and provides an important foundation for elucidating N. bombycis infection mechanisms.