The Ovarian Reserve of Primordial Follicles and the Dynamic Reserve of Antral Growing Follicles: What Is the Link?

International audienceThe growing follicles develop from a reserve of primordial follicles constituted early in life. From this pre-established reserve, a second ovarian reserve is formed, which consists of gonadotropin-responsive small antral growing follicles and is a dynamic reserve for ovulation. Its size, evaluated by direct antral follicular count or endocrine markers, determines the success of assisted reproductive technologies in humans and embryo production biotechnologies in animals. Strong evidences indicate that these two reserves are functionally related. The size of both reserves appears to be highly variable between individuals of similar age, but the equilibrium size of the dynamic reserve in adults seems to be specific to each individual. The dynamics of both follicular reserves appears to result from the fine tuning of regulations involving two main pathways, the PTEN/PI3K/PDPK1/AKT1 and the BMP/AMH/SMAD signaling pathways. Mutations in genes encoding the ligands, receptors or signaling effectors of these pathways can accelerate or modulate the exhaustion rate of the ovarian reserves, causing premature ovarian insufficiency or increase in reproductive longevity, respectively. With female aging, the decline in primordial follicle numbers parallels the decrease in the size of the dynamic reserve of small antral follicles and the deterioration of oocyte quality. Recent progress in our knowledge of signaling pathways and their environmental and hormonal control during adult and fetal life open new perspectives to improve the management of the ovarian reserves