Estradiol supports in vitro development of bovine early antral follicles

Antrum formation and estradiol (E(2)) secretion are specific features of oocyte and granulosa cell complexes (OGCs). This study investigates the effect of E(2) on the in vitro development of bovine OGCs derived from early antral follicles as well as on the expression of genes in granulosa cells (GCs). The supplementation of culture medium with either E(2) or androstenedione (A(4)) improved the in vitro development of OGCs and the nuclear maturation of enclosed oocytes. When OGCs were cultured in medium containing A(4), developmentally competent OGCs secreted more E(2) than OGCs that were not competent. In addition, fulvestrant inhibited the effect of both E(2) and A(4) on OGCs development. Comprehensive gene expression analysis using next-generation sequence technology was conducted for the following three types of GCs: i) GCs of OGCs cultured for 4 days with E(2) (1 μg/ml; E(2)(+)), ii) GCs of OGCs cultured for 4 days without E(2) (E(2)(-)) or iii) OGCs that formed clear antrum after 8 days of in vitro culture in medium containing E(2) (1 μg/ml; AF group). GCs of the E(2)(+) group had a similar gene expression profile to the profile reported previously for the in vivo development of large follicles. This genetic profile included factors implicated in the up-regulation of E(2) biosynthesis and down-regulation of cytoskeleton and extracellular matrices. In addition, a novel gene expression profile was found in the AF group. In conclusion, E(2) impacts the gene expression profile of GCs to support the in vitro development of OGCs.