Identification and sequencing of remnant messenger RNAs found in domestic swine (Sus scrofa) fresh ejaculated spermatozoa

The existence of specific messenger RNA remnants contained within freshly ejaculated spermatozoa was described in several species. Those investigations, using high-throughput techniques to screen the population of transcripts in ejaculated spermatozoa, were limited to the probes which mostly derived from nucleic acids of testicular tissues of either human or mice. The objective of this study was to investigate mRNA remnants from ejaculated spermatozoa of the domestic swine (Sus scrofa), a valuable model for biomedical research. A non-redundant 5′-end complementary DNA library was generated from swine ejaculated spermatozoa. After sequence quality verification, 4562 clones remained. These clones were then clustered and assembled into 514 unique sequences including 188 contigs (36.58%) and 326 singletons (63.42%), representing those clusters containing at least two clones and those clusters without having enough similarity with other clones. These unique gene sequences were annotated in Gene Ontology (GO) hierarchy; they included biological processes (38.7%), molecular functions (39.1%) and cellular components (40.3%). Based on the analysis, a broad spectrum of messenger RNAs existed in swine ejaculated spermatozoa and was closely correlated with nucleic acid binding, structural modifications, and transcriptional regulation. All of these categories are considered to have profound effects on the male reproductive system. Therefore, our work provides initial results on potential spermatozoal gene expression for future studies regarding the tightly regulated spermiogenic processes and later fertilization events.