Biogenesis and function of tRNA fragments during sperm maturation and fertilization in mammals (ICSI)

Parental dietary conditions can influence the metabolic traits of offspring. In mice, paternal consumption of low protein diet alters cholesterol and lipid metabolism of progeny. Here, we examine RNA species expressed in male reproductive tissues of mice. Protein restriction leads to altered levels of multiple small RNAs in mature sperm, as well as throughout the male reproductive tract, with decreased levels of let-7 family members and increased levels of 5’ fragments of tRNA-Gly isoacceptors. Intriguingly, tRNA fragments are scarce in the testis, but their levels increase in sperm during post-testicular maturation in the epididymis. We find that epididymosomes – extracellular vesicles which fuse with sperm during epididymal transit – exhibit RNA payloads closely matching those of mature sperm, and can deliver tRNA fragments to immature sperm in vitro both in mouse and in bull. Finally, we show that tRNA-Gly-GCC fragments play a role in repressing genes associated with the endogenous retroelement MERVL, both in ES cells and in preimplantation embryos. Our results shed light on small RNA biogenesis during post-testicular sperm maturation, and link tRNA fragments to regulation of endogenous retroelements active in the early embryo. Overall design: Zygotes were generated by ICSI from oocytes/females fed a Control diet and sperm/males fed either a Control or Low Protein diet. The sperm was isolated from either the Rete testis or the Cauda epididymis and injected either as a whole sperm or just the sperm head. Following fertilization by ICSI the zygotes developed for 28 hours (2C stage) and were harvested for single-embryo RNA-Seq.

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Sharma U, Conine CC, Shea JM, Boskovic A, Derr AG, Bing XY, Belleannee C, Kucukural A, Serra RW, Sun F, Song L, Carone BR, Ricci EP, Li XZ, Fauquier L, Moore MJ, Sullivan R, Mello CC, Garber M, Rando OJ