MicroRNA identity and abundance in porcine skeletal muscles determined by deep sequencing.

MicroRNAs (miRNA) are short single-stranded RNA molecules that regulate gene expression post-transcriptionally by binding to complementary sequences in the 3' untranslated region (3' UTR) of target mRNAs. MiRNAs participate in the regulation of myogenesis, and identification of the complete set of miRNAs expressed in muscles is likely to significantly increase our understanding of muscle growth and development. To determine the identity and abundance of miRNA in porcine skeletal muscle, we applied a deep sequencing approach. This allowed us to identify the sequences and relative expression levels of 212 annotated miRNA genes, thereby providing a thorough account of the miRNA transcriptome in porcine muscle tissue. The expression levels displayed a very large range, as reflected by the number of sequence reads, which varied from single counts for rare miRNAs to several million reads for the most abundant miRNAs. Moreover, we identified numerous examples of mature miRNAs that were derived from opposite sides of the same predicted precursor stem-loop structures, and also observed length and sequence heterogeneity at the 5' and 3' ends. Furthermore, KEGG pathway analysis suggested that highly expressed miRNAs are involved in skeletal muscle development and regeneration, signal transduction, cell-cell and cell-extracellular matrix communication and neural development and function.