Melatonin and cyclic adenosine monophosphate enhance the meiotic and developmental competence of porcine oocytes from early antral follicles during in vitro growth and pre-maturation culture.

Melatonin has been studied for its ability to improve oocyte quality and modulate cyclic adenosine monophosphate (cAMP) production. However, the effects of melatonin on the in vitro growth (IVG) of oocyte-cumulus-granulosa complexes (OCGCs) derived from early antral follicles (EAFs) have not been fully investigated. This study aimed to examine the effects of melatonin during IVG on the developmental competence and blastocyst quality of porcine oocytes isolated from EAFs. In addition, the combination of melatonin with dibutyl cAMP (Mela + dbcAMP) or hypoxanthine (Mela + HX) during IVG and pre-in vitro maturation (pre-IVM) was also investigated. The result showed that the modified medium supplemented with 10 μM melatonin after 4-day IVG enhanced antrum formation, survival rate, and oocyte diameter, especially, the melatonin-treated group enhanced expression of histone acetylation (Ac-H3-K9) higher than the untreated group. In addition, the combination of 10 μM melatonin with dbcAMP during IVG and during 7h of pre-IVM had significantly improved meiotic competence and cumulus expansion after IVM compared to Mela + HX groups. Finally, the combination of Mela + dbcAMP improved parthenogenetic blastocyst formation rather than the untreated group, and expression of histone methylation (Me-H3-K4) and Ac-H3-K9 in blastocyst comparable group derived from oocytes of large antral follicles (LAFs). Furthermore, melatonin with concentrations of 10 μM and 100 μM during IVG enhanced expression of pluripotency gene-related (OCT4, NANOG, SOX2) and balance cell viability via apoptosis-related gene (BCL2/BAX). In conclusion, melatonin combined with dbcAMP during IVG and pre-IVM of oocytes derived from EAFs demonstrated superior efficacy in enhancing oocyte growth, maturation, and development of porcine pre-implantation embryos.