miRNA-dysregulation associated with tenderness variation induced by acute stress in Angus cattle

MicroRNAs are one of the largest gene families and account for ~1% of the genome [1]. They are 21–25 nucleotide small, non-coding RNAs that post-transcriptionally repress the expression of protein-coding genes through binding to the 3’ untranslated regions (UTR) of the target mRNAs [1-5]. Accumulated evidence indicates that miRNAs are important in the regulation of many biological processes, such as developmental timing, cell metabolism, cell differentiation, cell death, cell proliferation, haematopoiesis and patterning of the nervous system, etc[1,4,6]. Recent studies have uncovered muscle-specific miRNAs that regulate diverse aspects of muscle function, including myoblast proliferation, differentiation, contractility and stress responsiveness [7-10]. Disruption of miRNA biogenesis causes diverse developmental defects, including abnormal embryogenesis and depletion of stem cells [4]. It has been reported that microRNA-133a regulates cardiomyocyte proliferation and suppresses smooth muscle gene expression in heart [8]. miR-1 and miR-133 have distinct roles in modulating skeletal muscle proliferation and differentiation in cultured myoblast in vitro and in Xenopus laevis embryos in vivo[9]. miR-335 and miR-126 are identified as metastasis suppressors in human breast cancer because their expressions are lost in the majority of primary breast tumors [11]. Additionally, miRNAs have been found involved in viral infections, cancer, cardiovascular disease and neurological and muscular disorders [6,12-20]. With the progression of research, a large number of miRNAs have been found to play roles in the regulation of metabolic process. Although there are 18226 entries in miRBase, representing hairpin precursor miRNAs and expressing 21643 mature miRNA products in 168 species, only a handful of miRNAs have been studies deeply, and a range of functions extending beyond developmental regulation have been revealed [4]. Especially, 665 miRNAs in bovine are shown in the database, and