Sperm RNA may predict embryo quality

Small RNA molecules in sperm are important for embryo development and may act as biomarkers for sperm and embryo quality, a new study has shown.

Researchers at the University of Linköping, Sweden, explored the relationship between small RNA fragments in sperm and quality of sperm and embryos. Small RNAs (sRNAs) are short fragments of ribonucleic acid involved in regulating gene expression as well as having other functions. Sperm cells are not only responsible for delivering chromosomal genetic material to the egg and resulting embryo, but also many sRNAs.

'We identified different subpopulations of sRNA in sperm that exhibit distinct profiles in clinical reproductive measurements, such as sperm concentration, fertilisation rate, and the rate of high-quality embryos,' said the authors of the paper published in Nature Communications. 'Our analysis identifies specific sRNA as highly promising biomarkers... providing insight into possible molecular mechanisms of male fertility and paternal contribution to embryonic development.'

The researchers recruited 69 couples who were undergoing IVF at a clinic in Linköpig. They used RNA sequencing to reveal which sRNAs were present in sperm samples and their abundance, and compared these with the outcomes of the IVF cycles.

Analysis of sRNAs in sperm samples revealed that overlapping populations of sRNAs were increased and decreased, respectively, in low- and high-sperm count samples. The team also identified sRNAs that were closely linked with sperm's ability to fertilise oocytes – 34 specific sRNAs were found to be associated with low fertilisation rate and all originated from the same genomic region.

Embryo quality was also found to be linked to sperm-borne sRNAs. The researchers discovered 16 micro-RNAs (miRNAs; a type of sRNAs) which were significantly associated with the quality of embryos in the IVF process. Many of these miRNAs have previously been found to regulate developmental processes such as embryogenesis and cell proliferation. These findings show that sperm-borne sRNAs may be directly involved in coordinating the early stages of embryo development after fertilisation.

Due to the differences in sRNA abundance between low- and high-quality sperm and embryos, the authors suggest that some of these could be used as early biomarkers to predict tissue quality and outcome during IVF treatment. In particular, the team found that certain sRNAs derived from the cell's ribosomes, RNA-protein enzymes which build proteins in the cell, are especially strong markers for embryo quality.

The authors point out that IVF patients often go through several failed cycles, incurring emotional, financial, and physical costs. They hope that their findings will 'contribute to clinical strategies improving embryo quality, lowering costs and reducing the need for additional treatment cycles.'