Abstract
Circular RNAs (circRNAs) are emerging as a novel class of noncoding RNAs which potential role as gene regulators is quickly gaining interest. circRNAs have been studied in different tissues and cell types across several animal species. However, a thorough characterization of the circRNAome in ejaculated sperm remains unexplored. In this study, we profiled the sperm circRNA catalogue using 40 porcine ejaculates. A complex population of 1,598 circRNAs was shared in at least 30 of the 40 samples. Generally speaking, the predicted circRNAs presented low abundances and were tissue-specific. Around 80% of the circRNAs identified in the boar sperm were reported as novel. Results from abundance correlation between circRNAs and miRNAs together with the prediction of microRNA (miRNA) target sites in circRNAs suggested that circRNAs may act as miRNA sponges. Moreover, we found significant correlations between the abundance of 148 exonic circRNAs and sperm motility parameters. Two of these correlations, involving ssc_circ_1458 and ssc_circ_1321, were confirmed by RT-qPCR using 36 additional samples with extreme and opposite sperm motility values. Our study provides a thorough characterization of circRNAs in sperm and suggests that circRNAs hold potential as noninvasive biomarkers for sperm quality and male fertility.
Highlights
Circular RNAs are emerging as a novel class of noncoding RNAs which potential role as gene regulators is quickly gaining interest. circRNAs have been studied in different tissues and cell types across several animal species
We have identified nearly 1,600 boar sperm circRNAs that are robustly present in most samples
The sperm circRNA repertoire showed similar circular genomic characteristics including the proportion of genomic overlap with protein coding and intergenic regions, the number of exons and the circRNA length (Fig. 1), when compared to data previously reported in other tissues from swine[23], human[17] or rat[24]
Summary
Circular RNAs (circRNAs) are emerging as a novel class of noncoding RNAs which potential role as gene regulators is quickly gaining interest. circRNAs have been studied in different tissues and cell types across several animal species. The top 15 most abundant exonic circRNAs encompassed genes related to sperm biology and male fertility including ATP6V0A2, PPA2, PAIP2 and PAXIP1 (Table 1). A total of 148 exonic circRNAs from 142 genes showed significant correlations between their abundance and sperm motility traits (Supplementary Table S4).
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