Effect of alanine supplementation during in vitro maturation on oocyte maturation and embryonic development after parthenogenesis and somatic cell nuclear transfer in pigs

The objective of this study was to examine the effect of alanine treatment during in vitro maturation (IVM) on oocyte maturation and embryonic development in pigs. To this end, we investigated the nuclear maturation, intraoocyte glutathione (GSH) content of IVM oocytes, and embryonic development after parthenogenesis (PA) and somatic cell nuclear transfer (SCNT). In addition, we analyzed the expression of genes associated with apoptosis and embryonic development in IVM oocytes, 4-cell stage embryos, and blastocysts produced via PA and SCNT. To determine the optimal concentration of alanine to promote the maturation and development of PA and SCNT embryos, various concentrations (0, 0.363, 1, 5, and 10 mM) of alanine were added to IVM medium during oocyte maturation. The proportion of metaphase II (MII) oocytes after IVM did not differ according to the concentration of alanine. However, significantly higher intraoocyte GSH content was observed in oocytes treated with 0.363 mM alanine compared with that in untreated oocytes. However, treatment of recipient oocytes with 5 or 10 mM alanine during IVM decreased the GSH content in mature oocytes compared to that in control oocytes. Oocytes matured in the presence of 0.363 mM alanine showed significantly increased rates of cleavage and blastocyst formation after PA and SCNT compared to untreated oocytes. PA and SCNT embryos from the 0.363 mM alanine-treated group of MII oocytes showed significantly higher transcript levels of POU5F1 and FGFR2, which are associated with oocyte quality and embryonic development, than the untreated group. Our results suggest that treatment of pig oocytes with 0.363 mM alanine during IVM improves embryonic developmental competence after PA and SCNT by increasing intraoocyte GSH content and increasing the mRNA expression of POU5F1 and FGFR2.