ABSTRACT
The first stage of folliculogenesis is represented by the formation of the primordial follicles, which occurs when oocytes that survive the process of germ cell cluster breakdown are individually surrounded with squamous pregranulosa cells and remain quiescent in the ovary until recruited into the growing pool throughout reproductive life. From the limited pool of primordial follicles, some are stimulated to growth and develop into primary and secondary preantral follicles before acquiring an antral cavity through a precise spatiotemporal expression and interaction of multiple genes. At the antral stage, most follicles undergo atresia; the few that survive reach the preovulatory stage under the cyclic gonadotropin stimulation that occurs after puberty. One of the follicles attains dominance over the rest of the cohort and, in response to the preovulatory surge of gonadotropins, releases the mature oocyte for fertilization. The residual follicle undergoes luteinization to become the corpus luteum (CL), a transient hormoneregulated ovarian organ that secretes progesterone (P) to support pregnancy [2-4].
