Transcriptomic profiling of the livers of blue catfish (Ictalurus furcatus) after infection with Edwardsiella ictaluri

We have utilized a high-density oligonucleotide microarray for catfish in order to study the transcriptomic responses of blue catfish following infection with E. ictaluri and to identify and develop important immune-related markers for future characterization and genetic mapping. Microarray analysis of the transcriptome profile of the blue catfish liver following infection with the Gram negative bacterium led to the identification of 103 differentially expressed transcripts. Results indicated the strong upregulation of several pathways likely involved in the inflammatory immune response. A multifaceted response to infection was observed, encompassing the complement cascade, iron regulation, inflammatory cell signaling, and antigen processing and presentation. The induction of several components of the MHC class I-related pathway following infection with an intracellular bacterium is reported here for the first time in fish. Taken together, the microarray results add to our understanding of the teleost immune responses and will provide a solid foundation for future functional characterization, genetic mapping, and QTL analysis of immunity-related genes from catfish. Keywords: Disease state analysis Global gene expression in the blue catfish liver 3 days after infection with virulent Edwardsiella ictaluri was measured utilizing a new 28K catfish microarray. Three replicate pools of RNA (n=25) for control fish and three replicate pools (n=25) for infected fish were analysed on 6 separate arrays. Gene calls from at least 6 probe pairs/transcript were generated in RMA, and normalized values from treatment and control replicates were compared in SAM to identify differentially expressed genes. Criteria of two-fold expression change and a 10% FDR rate were used to determine a set of significantly up- and down-regulated genes. Representative results were confirmed by real-time RT-PCR.