Interpretive Summary: Of rodents and ruminants: a comparison of small noncoding RNA requirements in mouse and bovine reproduction
By: Caitlin Vonderhoe
Globally, bovines are a highly significant source of milk and protein, but there are profound challenges in bovine reproduction. Losses of reproductive potential start at the cellular level; low germ cell fitness and embryo-intrinsic factors adversely affect both reproductive rates and offspring health. A recent review by Chukrallah et al., published in the Journal of Animal Science, argued that small-noncoding RNAs (sncRNAs) from germ cells may represent prominent molecular mechanisms that control early embryo development and germ cell fitness.
MicroRNAs (miRNAs) are the best studied class of sncRNAs and are expressed in most mammalian tissues and suppress protein-coding gene expression after transcription. piRNAs are another class of sncRNAs that are highly expressed in the reproductive organs that associate with PIWI proteins to create an active complex that actively suppresses certain protein-coding RNAs. Transfer RNA fragments (tRFs) may act as transgenerational signaling molecules or may silence transcripts similarly to miRNAs and endo-siRNAs.
Male germ cells primarily express piRNAs and miRNAs which are carried by mature sperm with tRFs. piRNAs are necessary for male fertility; they have been implicated in genome stabilization, regulation of protein coding transcripts and translational silencing. Relatively little is understood about the function of miRNA in in male germ cells, but most investigators agree that miRNAs drive male fertility. Female germ cells rely on sncRNAs to appropriately mature and function. However, female germ cells express miRNAs, endo-siRNAs, and piRNAs in a highly species-specific function. miRNAs are distinctly and differentially expressed throughout oogenesis in a species-specific fashion, making them a collection of biomarkers and regulators of female fertility. Bovids and murine females also differ in the significance of endoRNAs during oocyte development. Bovine embryos rely on maternally inherited pilRNAs and miRNAs for development and there is evidence in the murine that the male provides tRFs that are significant in determining early embryo success.
Although many correlations between sncRNAs and reproductive success have been made in the murine, greater, species-specific research needs to be done to fully elucidate the impact of sncRNAs on male and female fertility and embryogenesis in the bovid.