Somatic environment and germinal differentiation in antral follicle: The effect of FSH withdrawal and basal LH on oocyte competence acquisition in cattle

In most mammals, the ovarian follicle interacts with the oocyte during all the steps of folliculogenesis, but in large mono-ovulating species such as cows, the full competence of oocytes to become a viable embryo is mainly acquired in the last few days before ovulation in large follicles. Although some embryos after IVM and IVF of oocytes obtained from nondominant follicles can produce blastocysts, these are less competent (rate and quality) than the ones from dominant or preovulatory follicles. Therefore, the last few days of folliculogenesis are crucial for the final oocyte maturation before ovulation resulting in optimal gamete preparation for fertilization and post-fertilization events. In a natural cycle, this period is characterized by a low amount of circulating FSH and LH. This low LH or basal LH level is nonetheless sufficient to maintain follicular growth and differentiation leading to the conditions triggering the LH surge and ovulation. This article provides a review of the different concepts correlated to oocyte competence acquisition including FSH depletion and exposes the results of different transcriptomic experiments offering a novel perspective of the different elements important to adequate granulosa cells development during the exceptional low LH window.