Oviduct as a sensor of embryo quality: deciphering the extracellular vesicle (EV) mediated embryo-maternal dialogue.

Embryo-derived extracellular vesicles (EVs) may play a role in mediating the embryo-maternal dialogue at the oviduct during the preimplantation period of embryonic development, potentially carrying signals reflecting embryo quality. This study aimed to investigate the effects of bovine embryo-derived EVs on the gene expression of bovine oviductal epithelial cells, and whether these effects are dependent on embryo quality. Presumptive zygotes were cultured individually in-vitro in droplets of regular culture media till day 8 while evaluating their development. Conditioned media samples were collected at day 5 and pooled based on embryo development as good quality embryo media (conditioned by embryos that developed to blastocysts by day 8) and degenerating embryo media (embryos that degenerated after cleavage by day 2). EVs were isolated by size exclusion chromatography and supplemented to primary BOEC monolayer cultures to evaluate the effects of embryo-derived EV supplementation on their gene expression profile. Gene expression was quantified by both RNA sequencing and RT-qPCR. A total of 7 upregulated and 18 downregulated genes were detected in the good quality embryo-derived EV supplemented BOECs compared to the control. The upregulated genes included classical interferon-induced genes, such as OAS1Y, MX1, and ISG15, which have previously been reported to be upregulated in the oviductal epithelial cells due to the presence of embryos. Our results suggest that these effects could be linked to EV-mediated communication, therefore. demonstrating that embryo-derived EVs are involved in embryo-maternal communication at the oviduct. Moreover, the observed oviductal responses were dependent on the embryo quality, suggesting that this system could be used as an indirect method to evaluate the embryo quality.