Unveiling the molecular regulatory mechanisms of immune responses in the spleen of spotted sea bass (Lateolabrax maculatus) against Nocardia seriolae infection

Spotted sea bass holds significant economic importance in China's aquaculture sector. The outbreaks of bacterial diseases, especially caused by Nocardia seriolae (N.seriolae), have occurred frequently due to intensive farming. With the high morbidity and mortality, fish nocardiosis is one of the most serious problems faced by the aquaculture industry of spotted sea bass. However, the regulatory mechanism of immune response in spotted sea bass after N.seriolae infection remain elusive. In our study, we conducted a comprehensive examination of clinical symptoms and histological structures of the spleen, revealing noticeable pathological changes in diseased fish. Subsequently, we employed transcriptome sequencing of the spleen to investigate the effect of N.seriolae on spotted sea bass at 0 h, 48 h, 96 h and 120 h at transcriptome level. A total of 3031, 3597, and 4683 differentially expressed genes (DEGs) were unveiled in 48 h vs. 0 h, 96 h vs. 0 h and 120 h vs. 0 h, respectively. Up-regulated DEGs were significantly enriched in PRRs and cytokine related pathways, while down-regulated DEGs exhibited significant enrichment in autophagy related pathways, suggesting potential roles in immune modulation. Weighted co-expression network analysis (WGCNA) identified a blue module strongly linked to the immune response against N.seriolae infection, from which 10 hub genes were identified, including ilr2, tnfrsf9, c7 and so on. Moreover, our findings highlighted the involvement of alternative splicing (AS) in the immune response and found that pathogen infection also induced the AS events in some immune-related genes. Our study could shed new light on the molecular regulatory mechanisms underlying the immune response after N. seriolae infection in spotted sea bass, providing a basic guidance for the breeding of spotted sea bass with disease resistance in the future.