The discovery of sperm-carrying RNAs (mRNAs and small non-coding RNAs) has opened the possibility of paternal contributions that more than merely providing the DNA. Sperm-carrying miRNA and mRNA have been implicated as active players in early embryo development and transgenerational epigenetic inheritance. However, the relative contents and profiles of small RNA population carried by mature sperm remain undefined.

By analyzing small RNA deep-sequencing data from mature sperm, researchers at Institute of Zoology, Chinese Academy of Sciences revealed that the mature sperm contain a unique subset of highly enriched small RNA families derived from tRNAs. These small RNAs are most frequently 29-34nt in length, and unanimously match to 5’ halves of mature tRNAs. They were therefore termed as “mature sperm enriched tRNA-derived small RNAs” or mse-tsRNAs. mse-tsRNAs comprised 67.54% of all small RNA reads, while miRNAs only take up 4.61%. By analyzing the developmental origin, mse-tsRNAs were shown to increase drastically at late- or post- spermatogenesis, implicating regulated tRNA cleavage or/and selective concentrating mechanisms at these stages. The researchers also revealed that mse-tsRNAs are enriched in sperm head and thus could be delivered into oocytes during fertilization. Given the tRNA origin, mse-tsRNAs are evolutionarily conserved across most known vertebrate species; these results suggest that mse-tsRNAs might serve as an ancient paternal element with evolutionarily conserved functions.

These results were published in Cell Research: