Non-Invasive Biomarkers of Embryo Development in Cattle

MicroRNAs (miRNAs)  regulate the expression of genes in several biological processes and are secreted from cells into the extracellular environment where it is through they may act as signaling molecules. It has been shown that embryos also secrete miRNA into culture media. Currently embryos are largely assessed based on morphology which is not a strong indicator of developmental potential. Detection of miRNA differentially expressed from embryos of  differing developmental status in the IVF culture media, offers potential for biomarker development of embryo quality and a non-invasive method to assess embryo competence. The present study assessed the miRNA milieu in IVF culture media conditioned by embryos of differing developmental competence. Small-RNA sequencing of media conditioned by blastocyst and degenerate (embryos that failed to develop from the morula stage) embryos derived from three IVF experiments, revealed 11 miRNAs differentially expressed; all were higher in degenerate conditioned media. miRNAs identified were either known to bovine, known to other mammalian species or were novel bovine sequences that  mapped to the genome and were predicted to form hairpins. MiRNA expression of selected miRNA including mir-2887, miR-24, miR-146a, miR-191 and miR-148a, was validated by qRT-PCR in two additional biological replicates. These miRNA in other cell types regulate genes involved in cell proliferation, apoptosis and/or have been associated with fertility and embryonic development in previous studies. Further testing of miRNA in media of morphologically similar blastocysts offers potential to select embryos that may be genetically superior in terms of implantation rates and successful pregnancy outcome.