Inter - Species Analysis and Likely Functions of Sperm RNA

The spermatozoon is a highly complex cell which was thought to be transcriptionally inactive and solely delivers the paternal genome, centrioles and proteins to the
oocyte. During the past few years, a large number of different sperm RNA species have been discovered, however, the functionality and the gene expression networks
they may be involved remain unclear to date. Different studies showed that sperm RNAs provide a historical record of gene activity during spermatogenesis and that
they are delivered to the oocyte. The studies reported herein had the following foci:
Firstly, the spermatozoal transcriptomes of bovine, ovine, porcine and human were compared to their respective testis transcriptomes. Secondly, the spermatozoal
transcriptome of each species was analysed and compared to identify shared gene expression networks that may be indicative of common functionality in the processes
of spermatogenesis, fertilisation and reproduction. The results revealed common functional pathways, indicating a possible post-fertilisation role in the developing
embryo. In addition, bioinformatic analysis revealed 23 mutually shared transcripts.
To further characterise the potential transfer to the oocyte and to investigate the
potential function and stability of these paternal transcripts, 16 transcripts were selected and followed in the developing bovine embryo. No clear potential functions
for spermatozoal RNAs post-fertilisation and during embryo development could be derived from these experimental data.
Assisted reproductive processes and the breeding industry rely on freezing spermatozoa and choosing the best candidate spermatozoon. Therefore as an additional focus, RNA profiles of frozen and fresh spermatozoa from the same donor
were analysed and did not reveal major changes in the spermatozoal transcriptome caused by cryopreservation processes. Additionally as a last focus, the transcriptome
of hyaluronic acid (HA) selected spermatozoa was compared to unselected spermatozoa and revealed no significant differences in RNA expression. However, a trend towards an increased expression of MOSPD3 was observed and investigated
as a potential fertility marker. Expression of MOSPD3 protein was seen to be upregulated in motile spermatozoa compared to less motile by both Western Blot
analysis and immunocytochemistry. The present data supports the suggestion that sperm binding to HA may represent more viable populations and that MOSPD3 is a potential marker of spermatozoa viability that could be developed into a diagnostic tool.