Identification of miRNAs in Bovine Endometrium through RNAseq and Prediction of Regulated Pathways

Detection of miRNAs in reproductive tissues is a key step to understand their role in fertility. We hypothesize that miRNAs must be involved in pathways controlling endometrial physiology and defense against pathogens. In this study, we aimed to characterize miRNAs present in bovine endometrium and to predict regulated pathways. Cytobrush endometrial samples from four cows were collected at oestrous cycle days 1-5, 6-12, 13-18 and 19-21. RNA was extracted and sequenced using Ion Torrent (®) technology. After mapping of the reads to miRNA stem loops, rRNAs and tRNAs, data were normalized and analysed using DESeq2. Targets and pathways were predicted with miRmap and KEGG, respectively. Validation of miRNAs in tissue was done by RT-qPCR (miR-Q). A total of 221 identities were common among groups, accumulating more than 99% of miRNA expression. MiRNAs were predicted to regulate MAPK signalling pathway, lysosome and extracellular matrix (ECM)-receptor interaction. Eight miRNAs were validated by miR-Q, showing that let-7a-5p and let-7b were regulated across the oestrous cycle. This study demonstrated a high similarity in miRNA expression profile across the oestrous cycles in bovine endometrium. These miRNAs were predicted to regulate pathways involved in cell proliferation, differentiation, transport and catabolism. The number of pathways shared by different miRNAs indicates the broad range of regulation these molecules exhibit in the endometrium.