Initial and Cyclic Recruitment of Ovarian Follicles

Abstract

Mammalian ovaries consist of follicles as basic functional units. The total number of ovarian follicles is determined early in life, and the depletion of this pool leads to reproductive senescence. Each follicle develops to either ovulate or, more likely, to undergo degeneration. The dynamics of ovarian follicle development have interested endocrinologists and developmental biologists for many years. With the advent of assisted reproductive techniques in humans, the possibility of regulating follicle development in vivo and in vitro has gained clinical relevance. In this review, we focus upon key branching points during the development of ovarian follicles as well as factors involved in determining the eventual destiny of individual follicles. We discuss inconsistencies in the literature regarding the definitions of follicle recruitment and selection and propose to name the two major steps of follicle development as initial and cyclic recruitment, respectively. Because some of these disparities have arisen due to differences in the animal systems studied, we also compare the development of the ovarian follicles of both humans and rats. We also review the status of knowledge of several puzzling clinical issues that may provide important clues toward unlocking the mechanisms of follicle development.

Expression of Sox9 in granulosa cells lacking the estrogen receptors, ERα and ERβ

“…However, in contrast to their WT homologues, they are often separated from the follicular wall (Dupont et al, 2000), which could impair some of their interactions with granulosa cells. On the other hand, it is clear that follicular atresia, which may be increased in ER␣␤KO ovaries (Dupont et al, 2000) but also represents the normal fate of the vast majority of growing follicles in WT ovaries (reviewed in McGee and Hsueh, 2000), cannot, by itself, account for the ectopic differentiation of ovarian Sertoli cells.…”

Single nucleotide polymorphisms in the Anti-Müllerian hormone (AMH Ile49Ser) and Anti-Müllerian hormone type II receptor (AMHRII −482 A>G) as genetic markers in assisted reproduction technology

“…The expression pattern of AMH seems to be similar in mice and human ovary. AMH affects two major regulatory steps of folliculogenesis, the inhibition of primordial follicle recruitment and the modification of the follicle stimulation hormone (FSH) sensitivity of small antral follicles in the process of cyclic selection [11,12]. AMH exerts its biological effects through the AMH type II receptor (AMHRII), which in turn activates AMH type I receptor (AMHRI) and creates a downstream signaling pathway.…”

Induction of ovarian activity and ovulation in an induced ovulator, the maned wolf (Chrysocyon brachyurus), using GnRH agonist and recombinant LH

“…Female maned wolves housed individually exhibit a cyclical rise in estrogen concentration throughout the breeding season [24]. Because estrogen is produced by the granulosa cells of growing follicles [32], it is likely that ovarian follicles still grow and produce steroids even in the absence of a male. Thus, if a deslorelin implant is placed in the presence of growing follicles, the release of FSH and LH in response to the GnRH agonist may be sufficient to support preovulatory follicle growth and ovulation.…”