High-throughput sequencing reveals differential expression of miRNAs in yak and cattleyak epididymis

Cattleyaks (CY) are interspecific hybrids between cattle (Bos taurus) and yak (Bos gruniens, YK) exhibiting the same prominent adaptability and higher performances than YK. The main problem of this crossbreeding is that the males are sterile. Different series of events of spermatogenesis coordinate to regulate gene expressing, involving microRNAs (miRNAs). As non-coding ribonucleic acids (ncRNAs), miRNAs predominantly facilitate the regulation of gene expression at post-transcriptional stages and play important roles in the acquisition and maintenance of male fertility in reproduction. The function of miRNA in the male reproductive system extends from the testis into the epididymis, regulating gene expression and contributing to regional gene expression variations. RNA sequencing on biological replicates, we described differentially expressed miRNAs profiles for tissue from epididymis of YK and CY. In the present study, High-throughput sequencing analysis showed that 55 differentially expressed (DE) miRNAs were identified in the epididymis of YK and CY. Among these, 43 DE miRNAs were upregulated while the remaining 12 DE miRNAs were downregulated between epididymis of YK and CY. In addition, we identified that the top most important DE miRNAs, bta-miR-449c, bta-miR-539, bta- miR-136, bta-miR-504, bta-miR-31 and bta-miR-222 were involved in the process of sperm maturation in epididymis CY. It was identified that the bta-miR-449c and bta-miR-222 may play major roles in the process of sperm maturation, sperm quality, sperm count, sperm production and male infertility of CY. Furthermore, GO and KEGG analyses were performed to classify the functions of target genes for DE miRNAs. In addition, RT-qPCR validation of the DE miRNAs and its targeted genes revealed that putative miRNAs are involved in the male CY infertility by altering the gene expression. Present findings may not only increase our understanding of the molecular mechanisms regulated by the miRNAs in epididymis, but also provide a valuable information to understand the male infertility mechanism of CY.