The characteristics of the porcine (Sus scrofa) liver miRNAome with the use of next generation sequencing.

MicroRNAs (miRNAs) are a class of small, noncoding RNAs, which play a vital role in the regulation of gene expression by binding to the 3' untranslated region (3'UTR) of a target mRNA. Despite a significant improvement in the identification of miRNAs in a variety of species, the coverage of the porcine miRNAome is still scarce. To identify porcine miRNAs potentially regulating processes taking place in the liver, we applied next generation sequencing. As a result, we detected 206 distinct miRNAs, of which 68 represented potential novel miRNAs. Among these new miRNAs, there were miRNAs deriving from the opposite arm of a hairpin precursor of already known miRNAs. Moreover, we observed 3' and 5' length and sequence variants, probably constituting so called isomiRs, as well as differentially mapped precursor loci, alternative precursor sequences and clustering of miRNA encoding genes. On the basis of expression levels, reflected by the number of sequence reads, we identified the most abundant miRNAs followed by gene target prediction and pathway analysis. The enriched pathways were connected with cellular and metabolic processes, growth factors as well as enzymatic activity. The obtained results are the first ones to concern the porcine liver miRNAome. Consequently, they will increase the number of known porcine miRNAs and facilitate further research on gene regulation mechanisms as well as biological processes associated with the liver functioning in pigs.