Post-transcriptional regulation through alternative splicing after infection with Flavobacterium columnare in channel catfish (Ictalurus punctatus)

Columnaris disease has long been recognized as a serious problem worldwide which affects both wild and cultured freshwater fish including the commercially important channel catfish (Ictalurus punctatus). The fundamental molecular mechanisms of the host immune response to the causative agent Flavobacterium columnare remain unclear, though gene expression analysis after the bacterial infection has been conducted. Alternative splicing, a post-transcriptional regulation process to modulate gene expression and increase the proteomic diversity, has not yet been studied in channel catfish following infection with F. columnare. In this study, genomic information and RNA-Seq datasets of channel catfish were used to characterize the changes of alternative splicing after the infection. Alternative splicing was shown to be induced by F. columnare infection, with 8.0% increase in alternative splicing event at early infection stage. Intriguingly, genes involved in RNA binding and RNA splicing themselves were significantly enriched in differentially alternatively spliced (DAS) gene sets after infection. This finding was consistent with our previous study in channel catfish following infection with Edwardsiella ictaluri. It was suggested to be a universal mechanism that genes involved in RNA binding and splicing were regulated to undergo differential alternative splicing after stresses in channel catfish. Moreover, many immune genes were observed to be differentially alternatively spliced after infection. Further studies need to be performed to get a deeper view of molecular regulation on alternative splicing after stresses, setting a foundation for developing catfish broodstocks with enhanced disease resistance.