Abstract: 【Objective】This study was conducted to get a comprehensive understanding of miRNAs expression in sheep ovary, and to analyze their expression differences between sheep producing single lamb and twins, thus providing a basis for exploring the role of miRNAs in the regulation of fertility. 【Method】 Multi-species miRNA microarray was used to profile ovarian miRNAs expression in sheep. Firstly, single-lamb-producing and twin-producing ewes were selected. Ovaries were collected after estrus for total RNA extraction, and small RNA fragments were isolated and hybridized with miRNA microarray. Then data analysis was performed to obtain sheep ovarian miRNAs profile. Differentially expressed microRNAs were selected by bioinformatics software with the standard of q-value ≤ 5% and Fold Change ≥2 or ≤0.5, and q-PCR technique was employed to testify the microarray results. Two different methods, microT and miRDB, were used, respectively, and then data were merged and to predict target genes. Finally, online software was used to perform GO function annotation for target genes. 【Result】 Among all the detected miRNAs, a total of 5448 miRNAs were detected in sheep ovaries, of which 22 were specifically expressed in single-lamb-producing group, while 15 were in twin-producing group; For the miRNAs reported in sheep, expression differences were compared between two groups, and obtained 11 differentially expressed miRNAs, with 7 down-regulated and 4 up-regulated. Tow miRNAs were randomly selected to perform q-PCR validation, and the results were consistent with the microarray results, illustrating that the microarray results were accurate and credible. Target genes were obtained for 7 miRNAs: oar-miR-370-5p, oar-miR-376b-5p, oar-miR-381-5p, oar-miR-412-5p, oar-miR-541-3p, oar-miR-544-5p and oar-miR-1185-5p，and the number of target genes for each miRNAs was: 115, 71, 1, 5, 8, 135 and 23. The GO annotation results showed that target genes of miR-376b-5p and miR-1185-5p are mainly involved in forming intracellular components and organelles; in the molecular function category, the vast majorities of genes are the connection and catalytic activity molecules; in biological process, mainly involved in cell proliferation, differentiation, apoptosis and metabolism. Meanwhile, the target genes of miR-376b-5p ( IGF-1, DAZL, MTOR, MET and NEDD4 ) and miR-376b-5p ( AHR ) take part in reproduction regulation.【Conclusion】Sheep ovarian miRNAs expression profiling was successfully constructed, and differentially expressed miRNAs between single-lamb-producing and twin-producing sheep were obtained. These miRNAs may be involved in sheep follicular development and litter size regulation.

Key words: sheep, ovary, miRNAs, microarray