Effects of cobalamin on meiotic resumption and developmental competence of growing porcine oocytes

This study was performed to explore the effects of cobalamin treatment during in vitro maturation (IVM) of porcine oocytes. Specifically, the effects of cobalamin exposure on nuclear and cytoplasmic maturation of oocytes, diameter, glutathione (GSH) and reactive oxygen species (ROS) levels of matured oocytes, as well as development and gene expression of porcine parthenogenetic and cloned embryos were assessed. Cumulus-oocyte complexes were exposed to 200 pM cobalamin for 22 h or incubated for 22 h without cobalamin (controls). The mean diameter of cobalamin-treated oocytes was greater than that of control oocytes (160.0 vs. 154.5 μm; p < 0.05). GSH level increased but ROS level decreased in the cobalamin-treated oocyte group. Parthenogenetic embryos derived from cobalamin-treated oocytes showed improved oocyte maturation (91.3% vs. 83.8%), cleavage (88.9% vs. 82.1%), and blastocyst formation (38.7% vs. 31.9%) rates compared with control embryos (p < 0.05). Similarly, cloned embryos derived from cobalamin-treated oocytes showed higher oocyte maturation (89.2% vs. 82.2%), cleavage (87.5% vs. 80.3%), and blastocyst formation (30.0% vs. 23.8%) rates than control embryos (p < 0.05). Furthermore, in parthenogenetic and cloned embryos, total cell number, inner cell mass (ICM), trophectoderm (TE) expression, and ICM: TE ratio were higher in the cobalamin-treated group compared to that in the control group (p < 0.05). Cloned embryos in the cobalamin-treated group showed higher mRNA expression levels of POU5F1, DPPA2, and NDP52IL than control group embryos. Together, these results demonstrate that cobalamin treatment during IVM improves the developmental competence of porcine oocytes by neutralizing the free radicals produced in the IVM medium.