Effect of bovine oocyte transportation system on embryonic quality

The conventional ovum pick-up method requires oocytes to be transported from local farms to the laboratory, where they undergo nuclear maturation. However, atmospheric conditions for oocyte transportation differ from those for normal oocyte maturation in vitro. In this study, we examined the effects of conventional and modified oocyte transport conditions on oocyte quality and subsequent embryonic development. Cumulus-oocyte complexes were collected from slaughterhouse-derived bovine ovaries and cultured in few drops of medium on plastic plates in a CO₂-incubator (Control), in plastic tubes containing medium (C-T) in air, or in tubes containing gellan gum and medium (MC-T) in air. C-T conditions reduced mitochondrial functionality (mitochondrial membrane potential and adenosine triphosphate), lipid content, and DNA methylation but increased mitochondrial DNA copy number and phosphorylated AMP-activated protein kinase (P-AMPK) levels compared to those in control oocytes. Furthermore, RNA sequencing analysis of blastocysts derived from these oocytes revealed that C-T conditions affected mitophagy- and AMPK-signaling-related genes. However, MC-T conditions attenuated these C-T-associated changes. In conclusion, conventional C-T conditions affect oocyte metabolism and alter embryo quality, whereas the use of gellan gum as a substrate ameliorates such adverse effects. The oocyte transportation system is inadequate for embryonic production and can induce epigenetic changes. Modifying these conditions with gellan gum is a useful counter-measure.