The regulation roles of miR-125b, miR-221 and miR-27b in porcine Salmonella infection signalling pathway.

miRNAs are non-coding RNA molecules typically 18-22 nucleotides long that can suppress the expression of their target genes. Several laboratories have attempted to identify miRNAs from the pig that are involved in Salmonella infection. These bioinformatics strategies using the newly available genomic sequence are generally successful. Here, we report an in silico identification of miRNAs in pig focusing on the Salmonella infection pathway, and further investigated the differential expression of those miRNAs by quantitative real-time PCR during pre- and post-natal stage of Salmonella inoculation from the peripheral blood of commercially breed pigs. We identified 29 miRNAs that have predicted targets in the Salmonella infection pathway and nine of them were not yet described in pig. In addition, the expression of nine selected miRNAs was validated in the peripheral blood by northern blotting. Through expression analyses, differences were found between pre- and post-natal stages of Salmonella inoculation for miR-221, miR-125b and miR-27b-all of them were suppressed 2 days after Salmonella inoculation. The predicted targets of those three miRNAs were validated by luciferase reporter assays. We show that FOS is a direct target of miR-221, miR-125b can suppress MAPK14, and miR-27b can target IFNG. These findings will be helpful in understanding the function and processing of these miRNAs in Salmonella infection. The miRNA differentially expressed in the peripheral blood of commercial breed pigs suggest that it can be used as genetic markers for salmonella infection resistance in pigs.