Heterogenic origin of micro RNAs in Atlantic salmon (Salmo salar) seminal plasma

Abstract Background The origin and contribution of seminal plasma RNAs into the whole semen RNA repertoire are poorly known, frequently being overlooked or neglected. Virtually nothing is known about seminal plasma RNAs in fish, including small RNAs, which have regulatory functions in gonadal development. Results In this study, we profiled microRNA (miRNA) constituents in the whole semen, as well as in fractionated spermatozoa and seminal plasma of Atlantic salmon (Salmo salar). Among 306 conserved miRNAs, 85 were differentially accumulated (>2 log-fold change and p-value < 0.01) between spermatozoa and the seminal plasma. We identified a number of seminal plasma-enriched and spermatozoa-enriched miRNAs. We localized the expression of some miRNAs in juvenile and mature testes. Two abundant miRNAs, miR-92a-3p and miR-202-5p, localized to both spermatogonia and somatic supporting cells in immature testis, and they were also highly abundant in somatic cells in mature testis. miR-15c-5p, miR-30d-5p, miR-93a-5p, and miR-730-5p were detected only in mature testis. miRs 92a-3p, 202-5p, 15c-5p, and 30d-5p were detected also in a juvenile ovary in locations corresponding to these from the testis. Additional RT-qPCR experiment demonstrated lack of correlation in miRNA transcript levels in seminal plasma versus blood plasma. Conclusions Our results indicate that salmon semen is rich in miRNAs, which are present in both spermatozoa and seminal plasma. The latter ones have partially different profile indicating their heterogenic origin. Testicular supporting somatic cells are likely the source of seminal plasma enrichment, whereas blood plasma unlikely contributes to the seminal plasma miRNA repertoire.