Fig. 1

Folliculogenesis: Primordial follicles are surrounded with a single layer of squamous granulosa cells. With primordial activation, primordial follicles are recruited into folliculogenesis, initially becoming primary follicles with a single layer of cuboidal granulosa cells. With replication, granulosa cells form layers surrounding the oocyte, thus forming the secondary follicle. The early/small antral follicle is comprised of multiple layers of granulosa cells, which are differentiated into cumulus cells that immediately surround the oocyte as well as small pockets of antrum. The antral follicle is characterized by a large antrum containing follicular fluid, and is ready to be ovulated out of the ovarian cortex. Follicles can undergo atresia at any stage of folliculogenesis. AMH is secreted by preantral follicles and control primordial follicle recruitment as well as follicular atresia. In comparison, VEGF stimulates recruitment of primordial follicles to become primary