Bombyx moriにおけるRNA結合タンパク質SquidはAxin代替スプライシングを介して胚中腸発生を制御する

The insect midgut is crucial for digestion and nutrient absorption, but its embryonic development is poorly understood. Here, we show that the RNA-binding protein Squid is essential for embryonic midgut epithelium development in the model insect, Bombyx mori. CRISPR/Cas9-mediated knockout of Squid causes embryonic lethality, with mutants exhibiting disorganized midgut epithelium, lipid droplet accumulation, and impaired nutrient absorption. Integrated RNA sequencing (RNA-seq) and RNA-immunoprecipitation sequencing (RIP-seq) analyses reveal that Squid directly regulates the alternative splicing of Axin, a key Wnt/β-catenin pathway component. In Squid-depleted embryos, Axin splicing shifts from the long (Axin-L) to a short isoform (Axin-S), as confirmed by RT-qPCR. Consequently, β-catenin protein levels are significantly reduced in the midgut epithelium. Overexpression in BmN cells confirms that Axin-L, but not Axin-S, elevates β-catenin. Overall, this study uncovers a critical post-transcriptional pathway wherein Squid ensures proper midgut development by regulating Axin alternative splicing to fine-tune β-catenin levels.