Identification and characterization of miRNAs in the ovaries of a highly prolific sheep breed.

Until recently, there have been few studies concerning miRNAs or miRNA-mediated biological processes in sheep (Ovis aries). In the present study, we used a deep-sequencing approach to examine ovarian miRNAs and the mRNA transcriptomes in two ewes of a highly prolific breed, Finnsheep. We identified 113 known sheep miRNAs, 131 miRNAs conserved in other mammals and 60 novel miRNAs, the expression levels of which accounted for 78.22%, 21.73% and 0.05% of the total respectively. Furthermore, the 10 most abundantly expressed miRNAs in the two libraries were characterized in detail, and the putative target genes of these miRNAs were annotated using GO annotation and KEGG pathway enrichment analyses. Among the target genes, intracellular transducers (SMAD1, SMAD4, SMAD5 and SMAD9) and bone morphogenetic protein (BMP) receptors (BMPR1B and BMPR2) were involved in the transforming growth factor β (TGFβ) signaling pathway in the reproductive axis, and the most significant GO terms were intracellular part (GO:0044424), binding (GO:0005488) and biological_process (GO:0008150) for cellular component, molecular function and biological process respectively. Thus, these results expanded the sheep miRNA database and provided additional information on the prolificacy trait regulated through specific miRNAs in sheep and other mammals.