Abstract
The similarities and differences of small RNAs in seminal plasma, epididymal sperm and ejaculated sperm remain largely undefined. We conducted a systematic comparative analysis of small RNA profiles in pig ejaculated sperm, epididymal sperm and seminal plasma and found that the diversity distribution of small RNA species was generally similar, whereas the abundance of small RNAs is dramatically different across the three libraries; miRNAs and small RNAs derived from rRNA, tRNA, small nuclear RNA, 7SK RNA, NRON RNA and cis-regulatory RNA were enriched in the three libraries, but piRNA was absent. A large population of small RNAs from ejaculated sperm are ejaculated sperm specific, and only 8-30% of small RNAs overlapped with those of epididymal sperm or seminal plasma and a small proportion (5-18%) of small RNAs were shared in the three libraries, suggesting that, in addition to the testes, sperm RNAs may also originate from seminal plasma, epididymis as well as other resources. Most miRNAs were co-distributed but differentially expressed across the three libraries, with epididymal sperm exhibiting the highest abundance, followed by ejaculated sperm and seminal plasma. The prediction of target genes of the top 10 highly expressed miRNAs across the three libraries revealed that these miRNAs may be involved in spermatogenesis, zygote development and the interaction between the environment and animals. Our study provides the first description of the similarities and differences of small RNA profiles in ejaculated sperm, epididymal sperm and seminal plasma and indicates that sperm RNA may have origins other than the testes.
Highlights
For a long time, sperm RNA has been considered the residue of spermatogenesis and lacking in function because of its limited amount and special anatomical position
We compared the abundance and diversity of the small RNAs identified in ejaculated sperm with those found in epididymal sperm and seminal plasma to improve the understanding of their origins and regulatory roles
In addition to mRNAs, the diversity of the population of the sperm RNAs has been extended to several non-coding RNAs, including miRNAs, piRNAs (Amanai et al 2006, Krawetz et al 2011, Pantano et al 2015), endo-siRNAs (Yuan et al 2016), small RNAs derived from transfer RNA (tRNA), ribosomal RNA (rRNA), small nuclear RNA (snRNA) and small nucleolar RNAs (snoRNAs) (Peng et al 2012, Schuster et al 2016) and lncRNA (Sendler et al 2013)
Summary
Sperm RNA has been considered the residue of spermatogenesis and lacking in function because of its limited amount and special anatomical position. Both coding and non-coding RNAs have been well characterized in sperm (Jodar et al 2013), and it has been revealed that sperm can carry diverse RNA species (including mRNAs and small RNAs, some of which are sperm specific) to the fertilized zygote (Ostermeier et al 2004, Stoeckius et al 2014), indicating that these RNAs may play a unique paternal role in the development of zygotes. The spermborne mRNA Wnt was found to be delivered into the fertilized oocyte and translated, which represents evidence of a paternal effect on zygotic development (Fang et al 2014); the functional significance of sperm mRNAs in the development of zygotes remains largely unknown
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