Identification of candidate miRNAs and expression profile of yak oocytes before and after in vitro maturation by high‐throughput sequencing

Contents Small RNA represents several unique non‐coding RNA classes that have important function in a wide range of biological processes including development of germ cells and early embryonic, cell differentiation, cell proliferation and apoptosis in diverse organisms. However, little is known about their expression profiles and effects in yak oocytes maturation and early development. To investigate the function of small RNA s in the maturation process of yak oocyte and early development, two small RNA libraries of oocytes were constructed from germinal vesicle stage ( GV ) and maturation in vitro to metaphase II ‐arrested stage (M II ) and then sequenced using small RNA high‐throughput sequencing technology. A total of 9,742,592 and 12,168,523 clean reads were obtained from GV and M II oocytes, respectively. In total, 801 and 1,018 known mi RNA s were acquired from GV and M II oocytes, and 75 mi RNA s were found to be significantly differentially expressed: 47 mi RNA s were upregulated and 28 mi RNA s were downregulated in the M II oocytes compared to the GV stage. Among the upregulated mi RNA s, miR‐342 has the largest fold change (9.25‐fold). Six highly expressed mi RNA s (let‐7i, miR‐10b, miR‐10c, miR‐143, miR‐146b and miR‐148) were validated by real‐time quantitative PCR ( RT ‐ qPCR ) and consistent with the sequencing results. Furthermore, the expression patterns of two mi RNA s and their potential targets were analysed in different developmental stages of oocytes and early embryos. This study provides the first mi RNA profile in the mature process of yak oocyte. Seventy‐five mi RNA s are expressed differentially in GV and M II oocytes as well as among different development stages of early embryos, suggesting mi RNA s involved in regulating oocyte maturation and early development of yak. These results showed specific mi RNA s in yak oocytes had dynamic changes during meiosis. Further functional and mechanistic studies on the mi RNA s during meiosis may beneficial to understanding the role of mi RNA s on meiotic division.