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The role of activin-A in follicular development and on the mRNA expression levels of different genes in goat secondary follicles was evaluated. Goat secondary follicles (≥ 150 μm) were cultured for 18 days under control conditions or with the addition of either 50 or 100 ng/ml activin-A (Experiment 1). The mRNA levels for the genes that code for activin-A, ActR-IA, ActR-IB, ActR-IIA, ActR-IIB, follicle stimulating hormone receptor (FSH-R) and P450 aromatase were measured in each condition (Experiment 2). We observed that after 6 days of culture, the antrum formation rate was higher in cultures with added activin-A than in the cultured control (P < 0.05). The addition of 50 ng/ml activin-A increased the follicular growth rate in the final third of the culture (days 12-18), resulting in a higher percentage of meiosis resumption (P < 0.05). On day 6, the addition of activin-A (50 ng/ml) increased the levels of ActR-IA mRNA compared with the cultured control (P < 0.05). After 18 days, the addition of 50 ng/ml activin-A significantly increased the levels of its own mRNA compared with the non-cultured control. Moreover, this treatment reduced the mRNA levels of P450 aromatase in comparison with the cultured control (P < 0.05). Higher levels of P450 aromatase mRNA were found for both activin-A treatments compared with the non-cultured control (P < 0.05). No difference in estradiol levels was detected among any of the tested treatments. In conclusion, the addition of activin-A to culture medium stimulated early antrum formation as well as an increase in the daily follicular growth rate and the percentage of meiosis resumption.

Summary This study investigated the effect of three different culture media (α minimum essential medium (α-MEM), McCoy or TCM199 during the in vitro culture (IVC) of bovine isolated pre-antral follicles. Pre-antral follicles greater than 150 μm in size were isolated and cultured for 0 (control), 8 or 16 days in one of the abovementioned culture media. Follicles were evaluated for survival, growth and antrum formation at days 8 and 16. The results showed that TCM199 was the most suitable medium to preserve follicular viability and ultrastructure, resulting in the highest rates of antrum formation. In conclusion, TCM199 promotes the in vitro development of isolated pre-antral follicles without hampering follicular functionality by sustaining in vitro growth and antrum formation.