Characterization and expression analysis of microRNAs in Qira black sheep and Hetian sheep ovaries using Solexa sequencing

The role of microRNAs (miRNAs) in the regulation of mammalian reproduction has been demonstrated previously. However, only a few studies have assessed the role of miRNAs in the reproduction processes of sheep. The elucidation of miRNA expression profiles in the ovaries of different sheep breeds representing fecundity extremes will be useful in understanding the roles of miRNAs in sheep reproduction. In this study, two small RNA libraries were constructed from ovary tissue taken from Qira black sheep and Hetian sheep during the estrous period and then sequenced using the Solexa sequencing method. We obtained 9,565,212 and 9,563,426 high-quality reads from Qira black sheep and Hetian sheep, respectively. In total, 531 miRNAs, including 98 putative miRNAs, were identified. Among the conserved miRNAs, 125 known miRNAs were significantly differentially expressed in the Qira black sheep and Hetian sheep libraries, with 24 upregulated and 101 downregulated in the Hetian sheep compared to the Qira black sheep. Four differentially expressed miRNAs were analyzed using real-time quantitative PCR to validate the reliability of the Solexa sequencing results. These results provide a foundation for future research on the regulation of miRNAs in sheep fertility and enrich the sheep miRNA databases.