Of rodents and ruminants: a comparison of small noncoding RNA requirements in mouse and bovine reproduction

Abstract

Ruminants are major producers of meat and milk, thus managing their reproductive potential is a key element in cost-effective, safe, and efficient food production. Of particular concern, defects in male germ cells and female germ cells may lead to significantly reduced live births relative to fertilization. However, the underlying molecular drivers of these defects are unclear. Small noncoding RNAs, such as piRNAs and miRNAs, are known to be important regulators of germ-cell physiology in mouse (the best-studied mammalian model organism) and emerging evidence suggests that this is also the case in a range of ruminant species, in particular bovine. Similarities exist between mouse and bovids, especially in the case of meiotic and postmeiotic male germ cells. However, fundamental differences in small RNA abundance and metabolism between these species have been observed in the female germ cell, differences that likely have profound impacts on their physiology. Further, parentally derived small noncoding RNAs are known to influence early embryos and significant species-specific differences in germ-cell born small noncoding RNAs have been observed. These findings demonstrate the mouse to be an imperfect model for understanding germ-cell small noncoding RNA biology in ruminants and highlight the need to increase research efforts in this underappreciated aspect of animal reproduction.

Keywords: PIWI-interacting RNAs; bovids; bovine; mice; microRNAs; ruminants.

Figure 1.

Murine and bovine small noncoding RNAs in germ cells and early embryos. Basic stages of differentiation for male (blue) and female (pink, with associated orange somatic cells) germ cells and early embryos (green) shown with sncRNA populations detected therein. Bar thickness represents relative abundance, hashed bars presumptive populations. Relative abundance of germ cell transmitted sncRNAs indicated in boxes. Spg, spermatogonia; Spc, spermatocytes; R and E Spt, round and elongating spermatids; Spz, spermatozoa; Oog, oogonia; P Ooc, primary oocyte; PV Ooc, preovulatory oocyte; GV Ooc, ovulated (germinal vesicle) oocyte; S Ooc, secondary oocyte; Zyg, zygote; 2-cell and 16-cell, 2- and 16-cell embryo stages; Blast, blastocyst; MZT, maternal to zygotic transition.