Splicing factor SC35 inhibits Nosema bombycis proliferation by regulating the alternative splicing of Bmupp1

Alternative splicing is a crucial mechanism in higher eukaryotes that enhances the structural complexity of the transcriptome and augments protein functional diversity. The regulation of alternative splicing is governed by splicing factors, which influence disease development by modulating this process. Pebrine disease, caused by Nosema bombycis (N. bombycis) infection, is a significant disease affecting the sericulture industry. Recent years have seen an increase in omics research, with numerous biochemical and molecular biological studies focusing on the complex interactions among various biomolecules (genes, RNA, proteins, metabolites) within the silkworm (Bombyx mori). However, there is a paucity of research on the alternative splicing gene response of silkworm during N. bombycis infection, and the role of alternative splicing genes in this process remains unclear. This study analyzes a differential alternative spliced gene Bmupp1, which responds to N. bombycis infection in silkworm. Subcellular localization revealed that Bmupp1-X1 is located in the cytoplasm, while Bmupp1-X2, X3, and X4 are localized in the nucleus. Overexpression of Bmupp1 demonstrated that Bmupp1-X2 and Bmupp1-X4 exhibit uridine phosphorylase (UPP) enzymatic activity. Bmupp1-X2 and Bmupp1-X4 inhibit N. bombycis replication, while Bmupp1-X1 and Bmupp1-X3 have no effect. Mini-gene assays and RNA interference of the splicing factor SC35 revealed that SC35 regulates the alternative splicing of Bmupp1 in a dose-dependent manner, specifically influencing the splicing of Bmupp1-X2 and Bmupp1-X4. RT-qPCR analysis suggested that splicing factor SC35 may play distinct roles during the early and late stages of N. bombycis infection. In conclusion, during the early and late stages of N. bombycis infection, splicing factor SC35 regulates the alternative splicing of Bmupp1, thereby enhancing uridine phosphorylase enzymatic activity to suppress N. bombycis proliferation.