Improve The Developmental Competence Of Bovine Oocytes From Small Antral Follicles By Pre-Maturation Culture

Abstract

Recent studies have identified that fully grown oocytes collected from large antral follicles (4-6mm) could highly obtain full meiotic competence and successfully reached embryonic development into blastocyst stage. However, growing oocytes derived from small antral follicles (2-3mm) have been indicated difficult to achieve high maturation and developmental competence due to incompletely obtaining materials for in vitro maturation. Thus, a sub-culture known as pre in vitro maturation (pre IVM) with L-ascorbic acid supplementation during pre IVM was applied to support their development to the blastocyst stage. This study examined the effects of antioxidant agent – L-ascorbic acid on three main characteristics: The meiotic competence (cumulus expansion ability, maturation rate) and the developmental competence (cleavage rate) and quality of blastocyst (cell number of a blastocyst and histone modifications). This experiment compared the differences of basic pre IVM culture without supplemented L-ascorbic acid (AsA0) group and pre IVM culture with supplemented L-ascorbic acid at concentration 50µg/ml (AsA50). Besides that, fully grown oocyte was used as a positive control group and growing oocyte without prematuration culture was a negative control. The results claimed that with pre IVM method, not only the OCGCs showed a good quality of cumulus expansion, but also showed a higher maturation rate (74.86 ± 2.98%) and higher developmental rate (late blastocyst rate 21.93% ± 6.08) comparing to the group without pre IVM method. Interestingly, L-ascorbic acid treatment improved of cumulus expansion and increased maturation rate (80.34% ± 2.49%) as the same percentage of the positive control group. Moreover, the present result showed that AsA50 the high proportion in late blastocyst formation rate (30.57% ± 8.19) as well as the quality of blastocyst (55.0% number of blastocysts had over 80 cells per blastocyst). In addition, bovine parthenogenetic blastocysts of group AsA50 improved the acetylation of histone H3 at lysine 9 (35.7 ± 1.4) and reduced the methylation of histone H3 at lysine 9. In conclusion, the pre-maturation method can increase meiotic, developmental competence and quality of embryo of growing oocytes derived from small antral follicles. Especially, L-ascorbic acid with 50µg/ml was the optimal concentration supplemented in pre maturation culture, it could increase on maturation rate, late blastocyst formation rate as well as the quality of blastocyst.