Abstract
The origin and contribution of seminal plasma RNAs into the whole semen RNA repertoire are poorly known, frequently being overlooked or neglected. In this study, we used high-throughput sequencing and RT-qPCR to profile microRNA (miRNA) constituents in the whole semen, as well as in fractionated spermatozoa and seminal plasma of Atlantic salmon (Salmo salar). We found 85 differentially accumulated miRNAs 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 also detected in a juvenile ovary. The RT-qPCR experiment demonstrated lack of correlation in miRNA transcript levels in seminal plasma versus blood plasma. Our results indicate that salmon semen is rich in miRNAs, which are present in both spermatozoa and seminal plasma. Testicular-supporting somatic cells are likely the source of seminal plasma enrichment, whereas blood plasma is unlikely to contribute to the seminal plasma miRNA repertoire.
Highlights
Small RNAs are involved in the regulation of various genetic elements important for differentiation, proliferation, and apoptosis
53.8% mapped to the Atlantic salmon genome without a mismatch
Some enrichment was found for the size range 27–35 nts compared to spermatozoa (34.6% versus 17.9%), whereas the fraction of the size range 15–26 nts constituted 12.1% and 25.2%, in seminal plasma and spermatozoa, respectively (Table 1 and Figure 1A)
Summary
Small RNAs are involved in the regulation of various genetic elements important for differentiation, proliferation, and apoptosis. Mature gametes carry the parental information, which regulates early embryonic development [1]. This parental information includes paternal epigenetic patterns and elements [2,3,4], delivered through spermatozoa, which regulate embryonic transcription [5,6], and thereby imprint the fate of an embryo. The sperm contains different classes of RNAs, but very little is known about their functions. Several hypotheses on the role of sperm RNAs in embryonic development have been formed [8,9], yet these conjectures need further experimental validation
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