Expression of microRNAs and their target genes and pathways associated with ovarian follicle development in cattle

Development of ovarian follicles is controlled at the molecular level by several gene products whose precise expression leads to regression or ovulation of follicles. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression through sequence-specific base pairing with target messenger RNAs (mRNAs) causing translation repression or mRNA degradation. The aim of this study was to identify miRNAs expressed in ovarian follicles, localize their expression within the theca and/or granulosa layers and their putative target genes/pathways that are involved in bovine ovarian follicle development. By using miRCURY microarray (Exiqon) we identified 14 and 49 differentially expressed miRNAs (P < 0.01) between dominant and subordinate follicles in theca and granulosa cells, respectively. The expression levels of four selected miRNAs were confirmed by qRT-PCR. To identify target prediction and pathways of differentially expressed miRNAs Union of Genes option in DIANA miRPath v.2.0 software was used. The predicted targets for these miRNAs were enriched for pathways involving oocyte meiosis, Wnt, TGF-beta, ErbB, Insulin, P13K-Akt and MAPK signaling pathways. This study identified differentially expressed miRNAs in the theca and granulosa cells of dominant and subordinate follicles, and clearly implicates them in having important roles in regulating known molecular pathways that determine the fate of ovarian follicle development. Dominant and subordinate follicles were extrated from bovine heifers on day 2.5-3.5 of oestrus cycle. Theca and granulosa cells were isolated from each sample. Dominant and subordinate follicles in each tissue were compared.