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Review Series

The ovary: basic biology and clinical implications

JoAnne S. Richards1 and Stephanie A. Pangas2

1Department of Molecular and Cellular Biology and
2Department of Pathology, Baylor College of Medicine, Houston, Texas.

Address correspondence to: JoAnne S. Richards, Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Phone: 713.798.6238; Fax: 713.790.1275; E-mail: joanner@bcm.tmc.edu. Or to: Stephanie A. Pangas, Department of Pathology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Phone: 713.798.5898; Fax: 713.798.1493; E-mail: spangas@bcm.tmc.edu.

Published April 1, 2010

The classical view of ovarian follicle development is that it is regulated by the hypothalamic-pituitary-ovarian axis, in which gonadotropin-releasing hormone (GnRH) controls the release of the gonadotropic hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and that ovarian steroids exert both negative and positive regulatory effects on GnRH secretion. More recent studies in mice and humans indicate that many other intra-ovarian signaling cascades affect follicular development and gonadotropin action in a stage- and context-specific manner. As we discuss here, mutant mouse models and clinical evidence indicate that some of the most powerful intra-ovarian regulators of follicular development include the TGF-β/SMAD, WNT/FZD/β-catenin, and RAS/ERK1/2 signaling pathways and the FOXO/FOXL2 transcription factors.

Introduction

The ovary is a highly organized composite of germ cells (oocytes or eggs) and somatic cells (granulosa cells, thecal cells, and stromal cells) whose interactions dictate formation of oocyte-containing follicles, development of both oocytes and somatic cells as follicles, ovulation, and formation of the corpus luteum (the endocrine structure that forms from the ovarian follicle after ovulation and is required for establishing and maintaining pregnancy) (Figure 1). Many events in the adult ovary are controlled by two hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), secreted from the anterior pituitary gland under the control of pulses of gonadotropin-releasing hormone (GnRH) from the hypothalamus (Figure 1). Low-frequency GnRH pulses stimulate a slight increase in FSH levels early in a woman’s menstrual cycle, enhancing follicle growth, while high-frequency GnRH pulses lead to a sharp rise in levels of LH just before mid-cycle (an event known as the “LH surge”), triggering ovulation and formation of the corpus luteum (Figure 1). The ovary also has a key role in these processes, ensuring the timely release of fertilizable oocytes and the maintenance of luteal cell function, a necessity for pregnancy, by directing feedback mechanisms to the hypothalamus and pituitary. For example, estrogen produced by the cells of the developing follicle both inhibits GnRH production in the hypothalamus and elicits elevated GnRH pulses, which trigger the mid-cycle LH surge that initiates ovulation. Thus, fertility depends on highly orchestrated endocrine events involving multiple organ systems.

Summary of hormonal control of the ovary during follicle growth, ovulation,Figure 1

Summary of hormonal control of the ovary during follicle growth, ovulation, and luteinization. (A) Left: The pituitary gonadotropins FSH and LH are part of the hypothalamic-pituitary-gonadal axis that coordinately regulates the menstrual (in humans) or estrous (in nonhuman mammals) cycle by extensive feedback loops. FSH controls follicular granulosa cell (GC) growth and estradiol production, while LH controls ovulation and follicular luteinization. Right: A cross section of a mouse ovary is shown, demonstrating the main cell types and follicle stages. Ovarian follicles are composed of a single oocyte surrounded by somatic cells (granulosa cells) and thecal cells. Follicles grow from primordial (not shown) to primary and secondary stages independent of the pituitary gonadotropins. FSH stimulates growth to the preovulatory follicle stage, characterized by granulosa cells that directly surround the oocyte (cumulus cells) and those that make up the bulk of the wall of the follicle. Following the LH surge, the follicle erupts through the ovarian surface (OSE), and the remaining cells of the follicle terminally differentiate to form a corpus luteum. Original magnification, ×5. (B) Ovulation in the mouse. Left: The preovulatory follicle contains an oocyte surrounded by cumulus cells that are separated from the mural granulosa cells by a fluid-filled cavity. Middle: Following the LH surge, the COC undergoes a process called cumulus or COC expansion, in which the cumulus cells make and become embedded in a hyaluronan-rich matrix. Right: The cumulus cells accompany the oocyte into the oviduct following release of the entire COC from the ovarian follicle.Original magnification, ×40.

Disruption of this finely controlled network can lead to many clinical syndromes including premature ovarian failure (POF), polycystic ovarian syndrome (PCOS), ovarian hyperstimulation syndrome, ovulation defects, poor oocyte quality, and cancer. The goal of this Review is to cover some of the advances in our understanding of the basic biology of the mammalian ovary that may shed light on specific ovarian dysfunctions that lead to infertility. We primarily focus on recent developments using mouse genetic models to study follicle growth and ovarian function because of the inherent difficulty of obtaining human ovarian tissue at defined stages of follicular growth. We emphasize the roles of bone morphogenetic proteins (BMPs), activins, and SMADs, WNT signaling, and recently uncovered aspects of the FSH and LH signaling cascades. We focus on these areas because specific mutant mouse models have unveiled how these signaling cascades regulate critical events controlling follicular development, ovulation, and luteinization and because we believe that they have relevance to understanding ovarian dysfunctions in women.

Factors that control oocyte development, primordial follicle formation, and early follicle growth

Gonadal development. During embryogenesis, the mammalian gonad first develops adjacent to the urogenital ridges and is given the term the “bipotential” or “indifferent” gonad because it develops identically at this time in both male and female embryos. Differentiation into a testis (male) or ovary (female) does not occur until after the primordial germ cells (PGCs) have migrated from the yolk sac and colonized the indifferent gonad. In mice, colonization occurs approximately 9.5–11.5 dpc. Once the PGCs colonize the indifferent gonad, in female mice, they undergo a period of proliferation, followed by differentiation into oocytes that enter meiosis (at approximately E13.5), and in male mice, they differentiate into prospermatogonia that become quiescent until after birth. Development of germ cells into either male or female states depends on their interactions with the somatic cells of the gonad (see following paragraph) (Figure 2). Multiple growth factors modulate PGC mitosis, including members of the TGF-β family: activin, BMPs, and TGF-β1 (reviewed in ref. 1). In mice, BMPs have an important role in PGC proliferation, and BMP2 and BMP4 increase the number of PGCs in culture (2, 3). Bmp7-null mice have reduced numbers of germ cells after 11.5 dpc, likely as a result of a proliferation defect between 10.5 and 11.5 dpc (4). In humans, activin increases female germ cell proliferation before the germ cells enter meiosis (5), while in mice, activin and TGF-β inhibit PGC proliferation (6), indicating the possibility of species-specific regulation. In mouse ovaries, the regulation of activin or BMP function appears to be critical for germ cell survival, as mice lacking follistatin (which is encoded by the gene Fst), an extracellular antagonist of activin, have normal numbers of PGCs and germ cells at E11.5–15.5 but lose 90% of germ cells at E16.5, with an almost complete loss by birth (7).

Signaling pathways controlling ovarian follicle growth in the mouse.Figure 2

Signaling pathways controlling ovarian follicle growth in the mouse. PGCs are specified by the BMP pathway, then proliferate and migrate to the indifferent gonad. The BMPs are major determinants of PGC specification and proliferation in the mouse. During the postnatal period, clusters (or nests) of germ cells break down to form primordial follicles, which upon activation become primary follicles. Estradiol (E2) inhibits the breakdown of germ cell clusters to primordial follicles. A number of mice lacking oocyte transcription factors (TFs) (NOBOX, SOHLH1, SOHLH2, and LHX8) show loss of follicles at the primordial follicle–to–primary follicle transition or before primordial follicle formation (FIGLA). Foxo3 is also expressed in oocytes, and deletion of Foxo3 (or the PI3K inhibitor Pten) in oocytes results in premature activation of the primordial follicle pool and oocyte loss. Foxl2 is expressed in somatic granulosa cells, and deletion results in arrest and subsequent death of follicles before the primary follicle stage. FOXL2 also likely functions at late stages in folliculogenesis. NOBOX regulates other TFs (e.g., Pou5f1) and also Gdf9, the product of which is secreted by the oocyte to regulate granulosa cell function, including suppression of Inha. GDF9 and activin signal though SMAD2/-3. Regulation of activin by its inhibitors, such as inhibin or follistatin, is critical after the secondary follicle stage and involves many follicle stages. In vitro experiments implicate FOXO1 and ESR2 as important regulators in granulosa cells of growing follicles. FSH is a key regulator of the antral and preovulatory stage through multiple signaling cascades, and many of the FSH targets at the preovulatory stage are coregulated by activin (Fshr, Cyp19a1) and/or β-catenin (Cyp19a1). See text for discussion and references for each indicated gene pathway.

Several factors determine whether the gonad will be an ovary or a testis, including members of the WNT/FDZ/β-catenin (which is encoded by the gene Ctnnb1) signaling cascade. Ovaries of Wnt4–/– mice are abnormal and exhibit structures similar to testicular tubules (8), indicating that WNT4 is a determinant of the female gonad. Mutations in the human R-spondin homolog (RSPO1) gene, which encodes a WNT pathway adapter molecule, indicate that this molecule is also a primary female sex-determining factor (9). Specifically, XX individuals with a mutant RSPO1 gene exhibit testicular-like gonads, lack Müllerian structures (oviduct and uterus), and present masculinized external genitalia as a consequence of testicular androgen biosynthesis. Moreover, female Rspo1–/– mice also demonstrate gonadal sex-reversal and oocyte loss (910). Remarkably, mice lacking both WNT4 and the transcription factor forkhead box L2 (FOXL2) exhibit complete and functional sex reversal of the ovary to a testis in the XX genotype (11). These intriguing recent results document unequivocally that there are organizers of ovary versus testis development and that Rspo1, Wnt4, and Foxl2 are all important for ovary development, at least in mice. Furthermore, XY male mice engineered to express stable β-catenin, a downstream target of WNT signaling, exhibit partial male-to-female sex reversal with ovarian structures totally lacking germ cells or seminiferous tubule demise and germ cell loss (12). Thus, β-catenin also appears to be one key mediator of WNT signaling that is essential for normal ovary development, at least in the embryonic mouse gonad.

PGCs divide to form syncytia (nests or cysts) of oocytes that break down to form primordial follicles, which represent the quiescent follicle reserve in the ovary. Each primordial follicle contains an immature oocyte arrested early in meiosis, surrounded by a flattened epithelium that will eventually become the granulosa cells. Germ cell syncytia breakdown occurs prenatally in humans and shortly after birth in mice (Figure 2). It is associated with massive germ cell loss, such that oocyte numbers are reduced from approximately 6 million in the fetal human ovary to 1 million at birth (1315). Inappropriate germ cell syncytia breakdown can lead to the generation of polyovular follicles (i.e., follicles that contain more than one oocyte). Polyovular follicles are present in some mouse strains (16, 17), in mice with certain TGF-β family member mutations (e.g., mice overexpressing the α subunit of inhibin, a TGF-β family member that inhibits FSH secretion [ref. 18], mice lacking activin in granulosa cells [ref. 19], and mice lacking oocyte-expressed Bmp15 [ref. 20]), and in mice with altered Notch signaling (21). Polyovular follicles are also seen in human ovaries at birth, but rarely in adults (22). Follicles with more than one egg can be identified in women undergoing in vitro fertilization (IVF) procedures (23), but the clinical significance of polyovular follicles on fertility has not been established in humans; however, polyovular follicles are not a primary cause of infertility in mice (24, 25). This might be because individual oocytes develop at different rates within the same follicle (23), and while multiple oocytes might be developing inside the follicle, only one may be at the appropriate maturation stage to be fertilized. Polyovular follicle formation can be induced by exposure of neonatal mice to estrogen (2630). In this context, estrogen reduces activin expression, which suggests a direct role for activin in normal primordial follicle formation (19, 26). This effect of estrogen underscores the need for further research on the effect of endocrine disruptors — environmental and dietary compounds that act like hormones — in reproductive diseases. Along these lines, increasing evidence from rodent studies indicates that neonatal exposure to genistein, the phytoestrogen found in soy, disrupts normal reproduction (3036). The effects of phytoestrogens and other estrogen-like compounds on the reproductive tract, fertility, and reproductive cancers are not well understood.

Transcription factors and early follicle growth. A number of transcription factors whose expression, at least in adult tissues, appears to be restricted to germ cells or oocytes, are necessary for early folliculogenesis (Figure 2) (37). Factor in the germline α (FIGLA) was the first of these transcription factors to be identified (38), and Figla–/– mice are sterile because primordial follicles fail to form (39). Figla encodes a basic helix-loop-helix (bHLH) transcription factor that regulates expression of the zona pellucida genes Zp1, Zp2, and Zp3, which encode the egg coat (38). Other germline-expressed, bHLH transcription factor–encoding genes are known, including spermatogenesis and oogenesis bHLH transcription factors 1 and 2 (Sohlh1 and Sohlh2). Mice null for either gene have a similar female phenotype: postnatal oocyte loss leading to female sterility (40, 41). Both Sohlh1–/– and Sohlh2–/– mice have deficiencies in ovarian expression of other transcription factor–encoding genes: lim homeobox protein 8 (Lhx8), POU-type homeodomain-containing DNA-binding protein (Pou5f1; also known as Oct4), newborn ovary homeobox (Nobox), and Figla. Deletion of Nobox also causes female sterility and postnatal oocyte loss, and the gene product has been shown to directly regulate expression of growth differentiation factor 9 (Gdf9) and Pou5f1 (42, 43). It is unclear how these transcriptional networks intersect to control oocyte development; however, if a woman were to have impaired expression of any one of these transcription factors, evidence from mice indicates that she might develop POF. Indeed, while these transcription factors were first identified and functionally studied in mice, recent studies have discovered mutations in both NOBOX and FIGLA in women with POF (44, 45), highlighting the importance of mouse models for identifying candidate disease-causing genes in humans.

Disruption of the FOXL2-encoding gene leads to abnormal follicle development and POF in mice (46) and humans (47). As discussed in the previous section, Foxl2 is expressed in the early stages of gonadal development and has been shown to direct ovarian and oppose testis development. In early postnatal Foxl2-null ovaries, the expression of some genes increases, e.g., nuclear receptor subfamily 0, group B, member 1 (Nr0b1; also known as Dax1) and Wnt4, while the expression of others decreases, e.g., nuclear receptor subfamily 5, group A, member 2 (Nr5a2; also known as Lrh1), aromatase (Cyp19a1), Fst, and Apoa1. Additional genes regulated in the ovary by FOXL2 at later stages of follicle development include inhibin βB subunit (the product of which forms either inhibin B when in complex with inhibin α subunit or activin B when it homodimerizes), Nr5a2, sterol regulatory element–binding transcription factor 1 (Srebf1), PPARγ coactivator 1α (Ppargc1a), cholesterol side chain cleavage (Cyp11a1), and steroidogenic acute regulatory protein (Star) (4850). These results indicate that in addition to its role in embryonic ovarian development, FOXL2 likely affects specific basic metabolic aspects required for the proliferation and differentiation of somatic cells in the postnatal ovary. A missense mutation (402C→G) in human FOXL2 has been linked to adult forms of ovarian granulosa cell tumors (GCTs), the most common type of malignant ovarian sex cord–stromal tumor (51). This mutation is unlikely to disrupt FOXL2 DNA binding, but rather alters protein-protein interactions (51). While this study found that the 402C→G mutation rarely occurs in juvenile GCTs (51), juvenile GCTs show reduced expression of FOXL2 (52), indicating that FOXL2 may regulate multiple effects in granulosa cells that are context and stage specific.

Other members of the forkhead box transcription factor family also affect ovarian function. These include members of the FOXO family that are evolutionarily conserved and act downstream of insulin and IGF1, as well as FSH, to direct cell survival, apoptosis, and proliferation. Disruption of the Foxo3 gene in mice leads to inappropriate oocyte activation, premature entry of primordial follicles into the growing pool, and POF (53) (Figure 2). Upon exhaustion of the primordial follicle pool, ovaries become devoid of growing follicles and the mice become infertile. Conversely, forced overexpression of Foxo3 in oocytes reduces the number of growing follicles (54). As PTEN is a negative regulator of PI3K, its removal enhances PI3K activity, leading to increased phosphorylation of downstream targets, including AKT and FOXO3. As a consequence, oocyte-specific disruption of the Pten gene generates an ovarian phenotype identical to that of Foxo3–/– mice: premature oocyte activation and release of primordial follicles into the growing pool (55). Specific targets of FOXO3 that restrict oocyte activation and proliferation of surrounding somatic cells remain to be defined (56). Although not yet observed in humans, mutation in the FOXO3 gene might be the underlying cause of unexplained POF or streak ovaries (i.e., remnant gonadal tissue devoid of oocytes).

In contrast to FOXO3, which is expressed in oocytes, FOXO1 is expressed preferentially and at elevated levels in granulosa cells of growing follicles in mice and humans (Figure 2). Thus far, loss-of-function analysis of the role of this transcription factor in the ovary has been precluded because Foxo1-null mice are embryonic lethal (57). Although conditional alleles of Foxo1, Foxo3, and Foxo4 have been generated, they have not yet been disrupted in a cell-specific manner in the ovary (58, 59). However, expression of FOXO1 mutants in granulosa cells indicates that FOXO1 may affect specific genes controlling granulosa cell proliferation (60), differentiation (60), or metabolism (61). Expression of a constitutively active nuclear form of FOXO1 in granulosa cells both suppresses expression of cyclin D2 (Ccnd2), Cyp19a1, FSH receptor (Fshr), and LH/choriogonadotropin receptor (Lhcgr) and acts as a potent negative regulator of essentially all genes in the cholesterol biosynthetic pathway, including Srebf1 and Srebf2 (60, 61). Thus, FOXO1 appears to be a critical factor in granulosa cells. Because FOXO1 is a downstream target of FSH and IGF1 and is presumed to be critical for metabolic homeostasis, and possibly apoptosis, modulation of FSH, IGF1, or insulin signaling might lead to clinical problems and may underlie some cases of infertility associated with diabetes.

New regulatory mechanisms that control follicle growth and differentiation

FSH signaling pathways. Although many of the early stages of follicle growth occur independently of pituitary gonadotropins (i.e., FSH and LH), FSH is required for granulosa cell differentiation and these cells rely on FSH to facilitate follicular growth (Figure 2 and Figure 3). Although FSH activates adenylyl cyclase, leading to production of cAMP and activation of PKA, FSH also activates other signaling cascades independently of cAMP: for example, pathways involving PI3K (likely via an SRC tyrosine kinase) (62), RAS (62), or glycogen synthase kinase 3β (GSK3β) (63). Activation of PI3K leads to phosphorylation and activation of AKT, which in turn phosphorylates and thereby inactivates FOXO1 (63). Although, as mentioned above, the effects of disrupting Foxo1 expression in granulosa cells have not yet been analyzed in vivo, disruption of Pten expression in granulosa cells, which leads to increased activation of the PI3K pathway and therefore increased phosphorylation and degradation of FOXO1, results in enhanced proliferation of granulosa cells, ovulation, and formation of corpora lutea that persist for unusually prolonged periods of time (64). Surprisingly, although FOXO1 is expressed at elevated levels in granulosa cells, PTEN protein levels are remarkably low. Therefore, factors other than, or in addition to, PTEN are likely to control the PI3K pathway in granulosa cells. These results indicate that the functions of PI3K pathway components in granulosa cells are complex and likely to be stage and context specific (64). Consistent with this, disruption of Pten in somatic cells of the mouse ovary causes distinct effects from those observed when it is disrupted in oocytes, as described above (Transcription factors and early follicle growth) (5355). Furthermore, although natural mutations or disruption of Pten in other tissues lead to tumor formation, disruption of Pten only in granulosa cells does not lead to GCTs (64), perhaps because other factors affect the PI3K pathway in these cells. Because FOXO1 expression is high in human granulosa cells, this pathway is likely to be regulated in a manner similar to that in the mouse, but until we have Foxo1–/– mice, the precise functions in vivo will remain unclear.

LH-mediated pathways to ovulation and luteinization.Figure 3

LH-mediated pathways to ovulation and luteinization. LH induces ovulation, COC expansion, oocyte maturation, and luteinization in preovulatory follicles. These events are mediated by LH activation of the PKA pathway and NRIP1, which induce the expression of the EGF-like factors (AREG, EREG). AREG and/or EREG in turn activate the EGFR signaling cascade, including RAS and ERK1/2. This hypothesis is based on the observations that when Erk1 and Erk2 are disrupted in granulosa cells, global changes occur in gene expression patterns that control ovulation, COC expansion, resumption of meiosis, and luteinization. Moreover, activation of ERK1/2 is essential to turn off the FSH-regulated gene expression program that controls genes essential for preovulatory follicle growth and differentiation. C/EBPα and C/EBPβ, NR5A2 (also known as LRH1), and possibly PGR appear to be among the key transcription factors that are activated by ERK1/2 phosphorylation and affect ovulation and luteinization. Other transcription factors that are targets of ERK1/2 include members of the AP1 family and EGR1/3, whose specific functions in ovulation and luteinization remain to be defined. Additionally, oocyte-derived factors such as GDF9 and BMP15 affect cumulus cell and granulosa cell functions in a gradient-dependent manner. The functions of specific genes are discussed in the text. TK, tyrosine kinase.

During the later stages of follicular growth (Figure 2), activins and estradiol, the predominant estrogen in humans, enhance the actions of FSH (65, 66) (Figure 2). In mice, activins activate the transcription factors SMAD2/3 and SMAD4, which coordinately regulate several FSH-induced genes including those encoding the cell cycle regulator CCND2 and the steroidogenic enzyme aromatase (67), which converts theca cell–derived androgens to estradiol. Estradiol, acting primarily via estrogen receptor beta (ERS2), has recently been shown to suppress expression of phosphodiesterase 1C (Pde1c), thereby increasing intracellular levels of cAMP induced by FSH (66). Because activins facilitate proliferation of granulosa cells and enhance FSH actions, in part by increasing estradiol, these interactions may help explain why, when activin actions are unopposed by inhibins (as occurs in mice lacking inhibin α subunit, which is encoded by Inha), activins promote GCT growth. The WNT signaling target β-catenin has also recently been implicated in enhancing Cyp19a1 expression (68), indicating that FSH-induced phosphorylation of GSK3β may be physiologically relevant in activating this arm of the WNT signaling cascade (69). Although disruption of the Ctnnb1 gene in mice does not lead to overt changes in follicular development (70), proper activation of β-catenin in the adult ovary appears to be essential for normal tissue maintenance because overexpression of a constitutively active form of β-catenin leads to abnormal follicle development and, eventually, to development of GCTs (71). Moreover, the tumor phenotype induced by overexpression of the constitutively active form of β-catenin is enhanced when the tumor suppressor Pten is also concomitantly disrupted in granulosa cells, and these mice die by 6 weeks of age (72).

FSH and LH have recently been shown to activate RAS, in part via an SRC tyrosine kinase–mediated process, leading to the phosphorylation and activation of downstream kinases, in particular MEK1 and ERK1/2 (62) (Figures 2 and 3). Strikingly, KRAS is expressed at high levels in the granulosa cells of both small follicles and antral follicles (follicles at the late stages of follicular development that are characterized by the presence of a fluid-filled cavity known as the antrum adjacent to the oocyte; Figures 1 and 2), but its role remains to be determined (73). Expression in granulosa cells of a constitutively active form of KRAS that is frequently associated with various cancers, including ovarian surface epithelial (OSE) cell cancer (KRASG12D), does not stimulate proliferation or tumor formation (73). Rather, KRASG12D-expressing granulosa cells cease dividing, do not undergo apoptosis, and fail to differentiate; that is, they are cell-cycle arrested. As a consequence, small abnormal follicle-like structures devoid of oocytes persist and accumulate in the ovaries of the KRASG12D mutant mice. Even when Pten is disrupted in KrasG12D mutant mice, GCTs do not form (74), which indicates that granulosa cells are extremely resistant to the oncogenic insults of mutant Kras and loss of Pten. By contrast, if the Kras and Pten mutations are engineered in OSE cells, aggressive tumors appear within 6 weeks of age (74). These results indicate that the elevated levels of FSH or LH observed in patients with POF or PCOS may lead to increased activation of the RAS/ERK1/2 pathway as well as the PKA pathway, causing an imbalance in granulosa cell functions. These pathways need to be analyzed in more detail in clinical samples.

TGF-β family members. The TGF-β family of growth factors has wide-ranging roles in female reproduction (75). Although various family members are expressed by the major ovarian cell types (i.e., oocytes, granulosa cells, and thecal cells) (Figures 1 and 2), many of their effects center on the control of granulosa cell growth and differentiation, both of which affect folliculogenesis and oocyte development. Disruption in the ovarian function of the TGF-β family has resulted in mouse models that mimic human diseases such as POF. For instance, follistatin is an extracellular binding protein that binds to members of the TGF-β family and acts as a ligand antagonist. Fst conditional knockout female mice have been generated using Amhr2-cre, which expresses cre recombinase in adult female ovaries, predominantly in granulosa cells (76, 77). These mice demonstrate some aspects of POF, with few remaining follicles found by eight months of age (76). In addition, Fst conditional knockout mice show increased levels of gonadotropins, with decreased serum testosterone, mimicking the hormonal profile observed in women with POF. However, mutations associated with follistatin in human cases of POF have not been reported. The mechanism behind the premature loss of fertility in Fst conditional knockout mice is unknown, but because follistatin is a strong inhibitor of activin, part of the phenotype potentially results from increased activin activity.

Lack of inhibin α also results in increased activin because inhibins and activins are related proteins that share common β subunits: inhibin A is a heterodimer of the inhibin α and βA subunits, and inhibin B is a heterodimer of the inhibin α and βB subunits, while activin A and B are homodimers of inhibin βA subunit and inhibin βB subunit, respectively. Inhibins are also functional antagonists of activins (7880). Inha–/– mice develop sex cord–stromal tumors as adults and die of cancer cachexia-like syndrome (81, 82). In addition, Inha–/– female mice are infertile prior to gross tumor development, as determined by their inability to ovulate and the lack of late-stage follicle development (83). Inhibin does not appear to be essential for embryonic oocyte development, germ cell syncytia breakdown, or primordial follicle formation because the ovaries of newborn Inha–/– mice have normal numbers of oocytes and develop equivalent numbers of primordial follicles as the ovaries of wild-type mice in the three days after birth (84). However, marked changes in the ovaries of Inha–/– and wild-type mice occur during the period of secondary follicle to early antral follicle development (Figure 2), which occurs after 6 days of age. At this point, ovaries in Inha–/– mice are much larger and contain more advanced follicle types than those in wild-type mice. In addition, granulosa cell growth is uncoupled from oocyte growth, as evidenced by overly large follicles containing inappropriately small oocytes. The lack of oocyte growth is likely related to decreased expression of Kitl, as the gene encoding the receptor for the Kitl gene product is expressed in oocytes and is critical for oocyte growth and development (85). Both GDF9 and activin are known to decrease expression of Kitl (19, 86), and both Gdf9 and the genes encoding inhibin βA and βB subunits are overexpressed in Inha–/– ovaries (84). Additionally, there is loss of oocyte-expressed Bmp15 and granulosa cell–expressed anti-Müllerian hormone (Amh), two growth factors that also modulate follicle growth. Thus, deletion of Inha results in multiple changes in the local hormonal milieu and causes infertility.

Mice lacking inhibin βA subunit (and thus lacking activin A and inhibin A) die shortly after birth (87), while mice deficient for inhibin βB subunit (and thus lacking activin B and inhibin B) have normal size litters but defects in nursing (88). Ovaries from inhibin βB subunit–deficient females overproduce the inhibin βA subunit (88), suggesting a possible compensatory gain in activin A activity. However, activin A and activin B are not fully redundant. For example, generating a mouse that expresses inhibin βB subunit in place of inhibin βA subunit rescues the perinatal lethality and craniofacial defects of inhibin βA subunit deficiency but is insufficient for normal folliculogenesis and female reproduction to occur (89). Moreover, stepwise removal of activin subunits by conditional deletion in granulosa cells culminates in female sterility only when all activin subunits are absent (19). In the activin-deficient ovary (conditional deletion of inhibin βA subunit in granulosa cells with global deletion of inhibin βB subunit), there are multiple defects in folliculogenesis (19). The most obvious is the progressive accumulation of corpora lutea, which is accompanied by increases in serum FSH and progesterone. As noted above, in granulosa cells, activin appears to play a predominant role as a growth promoter, and in support of this hypothesis, no ovarian tumors develop in activin-deficient mice. The growth-promoting role of activin in GCTs has been established by demonstrating that GCT growth in Inha–/– mice is slowed by deletion of the gene encoding the activin type II receptor; deletion of Smad3, which encodes a transcription factor that acts downstream of activin; or injection into mice of a chimeric activin binding receptor–murine Fc protein (81, 82, 9093).

SMAD transcription factors are key intracellular mediators of the canonical TGF-β family signaling pathway: SMAD2 and SMAD3 (AR-SMADS) signal downstream of activin, GDF9, and TGF-β, while SMAD1, SMAD5, and SMAD8 (BR-SMADS) signal downstream of the BMPs and AMH. An additional SMAD, SMAD4, participates in signaling triggered by all members of the TGF-β family. Conditional mutations of all SMADs have been generated in granulosa cells either as single or multiple mutations (9496). Conditional deletion of Smad4 results in age-dependent infertility, and because SMAD4 is involved in mediating signals triggered by all members of the TGF-β family, the phenotype affects multiple stages of folliculogenesis. Ovaries in Smad4 conditional knockout mice show defects in steroidogenesis, ovulation, and the function of cumulus cells (which are a subpopulation of granulosa cells whose main functions in developing follicles are to support oocyte development), and the mice eventually develop POF (95). Unlike in activin-deficient mice, ovaries in Smad4 conditional knockout mice exhibit increased preantral follicle death, a decrease in the number of antral follicles, and no accumulation of corpora lutea. Similar to the activin-deficient ovary, small follicles luteinized prematurely, and even though SMAD4 is a known tumor suppressor gene, no tumors developed in Smad4 conditional knockout mice.

A similar phenotype to Smad4 conditional knockout female mice is seen in female mice with granulosa cell conditional knockout of Smad2 and Smad3 (94). SMAD2 and SMAD3 have redundant functions in granulosa cells because mice with single conditional knockout of either Smad2 or Smad3 in granulosa cells have no reproductive phenotype (94). However, mice lacking both proteins have reduced litter sizes and become infertile after five months of age with disrupted follicle development (i.e., increased preantral follicle atresia and fewer antral follicles), luteinized follicles, reduced ovulation, and severe defects in cumulus cell function. The phenotypes of mice with conditional knockout of the BR-SMADs differ dramatically from those of other SMAD conditional knockouts. Single granulosa cell conditional knockout of either Smad1 or Smad5 and global Smad8 knockout generates mice that are viable and fertile, as are double granulosa cell conditional knockout Smad1/Smad8 and Smad5/Smad8 mice (96). However, double granulosa cell conditional knockout Smad1/Smad5 mice and triple granulosa cell conditional knockout Smad1/Smad5/Smad8 female mice demonstrate infertility with age and develop GCTs with full penetrance by three months of age. The BR-SMAD phenotype is similar to the juvenile form of human GCTs (97). In addition, the majority of double granulosa cell conditional knockout Smad1/Smad5 and triple granulosa cell conditional knockout Smad1/Smad5/Smad8 mice show peritoneal implants and lymphatic metastases over time. These mice were the first in vivo demonstration that the BR-SMADs may have a critical tumor suppressor function in ovarian granulosa cells (96).

The various phenotypes of the SMAD and activin/inhibin knockouts in the ovary suggest potential interactions between the BMP and TGF-β/activin signaling pathways, in particular the observation that Inha–/– and BR-SMAD conditional granulosa cell knockout mice develop GCTs (Figure 2). Part of the phenotype of Inha–/– mice can be attributed to the tumor-promoting activity of activin via SMAD3 (94). In the BR-SMAD conditional granulosa cell knockout mice, an examination of the phosphorylation status of the AR-SMADs demonstrated that SMAD2 and SMAD3 are nuclear and phosphorylated, indicating pathway activation. Thus, it has been suggested that part of the phenotype of the BR-SMAD conditional granulosa cell knockout mice may be due to dysregulation of the AR-SMADs (i.e., SMAD2 and SMAD3) (96) that promotes granulosa cell proliferation. The role of additional signaling pathways in tumorigenesis in the BR-SMAD conditional granulosa cell knockout mice is still under investigation. In addition, as members of the TGF-β family signal though SMAD-independent pathways — including ERK1/2, JNK, PI3K/mTOR, and p38 MAPK pathways (98101) — it is possible that tumor development results from activation of one or more of these noncanonical pathways by the BMPs when the BR-SMADs are not present.

New insights into factors controlling ovulation and luteinization

The LH surge terminates preovulatory follicle growth and initiates the processes of ovulation, oocyte meiosis, expansion of the cumulus cell oocyte complex (COC) (during which cumulus cells make a hyaluronan-rich matrix that surrounds the oocyte prior to ovulation), and luteinization (Figure 3) (102, 103). As a consequence, the FSH program of gene expression is turned off while genes controlling matrix formation and luteinization are turned on (74). Recent studies show that the LH surge stimulates not only PKA but also PI3K/AKT and RAS signaling cascades, and that each of these is critical for ovulation (73). LH rapidly induces in granulosa cells the expression of the EGF-like factors amphiregulin (AREG), betacellulin (BTC), and epiregulin (EREG) (104) in a PKA-dependent manner. These factors bind their cognate receptors present on granulosa cells and cumulus cells, activate RAS, and induce expression of downstream target genes, including hyaluronan synthase 2 (Has2), prostaglandin-endoperoxide synthase 2 (Ptgs2), and TNF-α–induced protein 6 (Tnfaip6), each of which is a target of ERK1/2 in cultured cells (103). Disruption of the EGF ligand/receptor signaling pathway in mice compromises ovulation, indicating that activation of this pathway is essential for LH-induced ovulation to occur (105). Moreover, mice in which ERK1 and ERK2 have been disrupted in granulosa cells exhibit normal follicle growth, but in response to LH, the COCs fail to expand, oocytes fail to re-enter meiosis, and follicles fail to either ovulate or luteinize (106). Genes expressed in preovulatory follicles fail to be suppressed, and genes known to regulate COC expansion, ovulation, and luteinization fail to be induced or activated. Thus, ERK1/2 controls a master switch that mediates the global reprogramming of granulosa cells downstream of EGF-like–factor activation of the EGF receptor pathway. Strikingly, ERK1/2 are also essential in the female mouse pituitary to initiate the LH surge (107). Thus, both the pituitary and the ovary exhibit ERK1/2 dependence during this critical process of ovulation and luteinization. The extent to which the activation of the ERK1/2 kinases is altered in infertile women has not been thoroughly examined.

Several transcriptional regulators are known to affect ovulation and appear to help mediate the effects initiated by ERK1/2 (Figure 3). Mice lacking nuclear receptor–interacting protein 1 (Nrip1; also known as RIP140) exhibit impaired ovulation and reduced expression of Areg, Ereg, and other ovulation-related genes (108). Therefore, NRIP1 may regulate transcription of the Areg gene, a critical early event in the ovulation process. Targeted disruption of Nr5a2 in granulosa cells blocks ovulation and luteinization with little effect on the early stages of follicular development (109), indicating that NR5A2 (also known as LRH1) may be an ERK1/2 target in preovulatory follicles. By contrast, NR5A1 (also known as SF1) is essential for pituitary, gonad, and adrenal formation (110). Conditional deletion of the Nr5a1 gene in granulosa cells shows that NR5A1 is essential for proper early follicle formation and development but does not appear to compensate for NR5A2 in granulosa cells of ovulating follicles (111). In this in vivo context, these two nuclear receptors appear to exhibit distinct, rather than overlapping, functions (112). The differences in the functions of NR5A1 and NR5A2 appear to be related to genes that are selectively regulated by NR5A1 (e.g., Amh and Inha) (111) compared with NR5A2 (e.g., Cyp19, Sult1e1, Cyp11a1, Nos3, and Ptgs2) (109). Targeted disruption of the NR5A2-regulated gene estrogen-specific sulfo-transferase (Sult1e1) leads to impaired ovulation and cumulus expansion (113), suggesting that NR5A2 potently induces expression of this gene in response to the LH surge. Because endogenous estradiol levels are high in Sult1e1–/– mice, this may contribute to the anovulatory phenotype, but the exact molecular mechanisms affected by high estradiol at this time have not yet been defined. One other mutant mouse in which both ovulation and luteinization are impaired is the CCAAT/enhancer-binding protein β (C/EBPβ)-deficient mouse (114). Importantly, C/EBPβ is a known phosphorylation target of ERK1/2 in granulosa cells (106). Based on the genes regulated by ERK1/2, NRIP1, NR5A1, and C/EBPβ, it is tempting to speculate that NRIP1 may be an important co-regulator and/or activator of NR5A1 and/or C/EBPβ in the ovary and that ERK1/2 may be required for specific phosphorylation events. Thus, it will be important to determine how ERK1/2, C/EBPβ, NR5A1, and NRIP1coordinately regulate a select number of genes that control ovulation versus luteinization. Clearly, ovulation defects in women could be attributed to altered functions in one or all of these factors.

The expression of genes frequently associated with innate immune responses, many potent cytokines, such as IL-6, and runt-related transcription factor 1 (RUNX1) and RUNX2 are also impaired in mice lacking ERK1/2 (103, 115117) (Figure 3). Recently, IL-6 alone has been shown to stimulate COC expansion and induce the expression of specific genes encoding proteins involved in this process (115). These observations indicate that in clinical situations where levels of IL-6 are elevated, such as chronic infections, endometriosis, and possibly PCOS, this and other cytokines may disrupt normal granulosa cell and cumulus cell functions. Moreover, IL-6 and leukemia-inhibitory factor (LIF) increase the expression of Stat3 and IL-6 signal transducer (Il6st) in cumulus cells and the oocyte present in preovulatory follicles and enhance reproductive outcomes, suggesting that this pathway impacts oocyte quality (115). Mice lacking IL-6st exhibit defects in zygotic cell division, suggesting that IL-6 and related cytokines affect oocyte functions (118). Whereas inclusion of IL-6 or LIF might improve the quality of oocytes obtained in IVF procedures in women, abnormally elevated levels of cytokines, as occurs in endometriosis and chronic infections, might impair oocyte quality in women. Because the induction of IL-6 is regulated not only by AREG (115) but also by progesterone receptor (PGR) (115, 119) and C/EBPβ, both of which are essential for ovulation, it is tempting to speculate that IL-6 may mediate some key process downstream of PGR and C/EBPβ in granulosa cells or cumulus cells. Moreover, the expression of synaptosomal-associated protein 25 (SNAP25), an important component controlling neuronal-like secretion of cytokines from granulosa cells, is also regulated by PGR (120). Thus, the importance of locally produced and secreted ovarian cell–derived cytokines during ovulation needs to be analyzed further, and these cytokines may affect several ovulation-related processes including follicle rupture, COC transport, and fertilization (117). In this regard it is important to note that cytokines have recently been shown to affect the fertilization process by enhancing sperm motility and capacitation.

Conclusions

New insights into regulators of early oocyte development, follicle formation, follicular growth, ovulation, and luteinization indicate that multiple factors and signal transduction pathways act in cell- and context-specific manners to regulate fertility. Analyzing these genes might provide new targets for contraceptive research as well as improve fertility in women with endometriosis and PCOS. The ability to manipulate the size of the primordial follicle pool opens up the possibility of extending ovarian function, not only for reproductive purposes, but also to diminish the effects of diseases associated with menopause, such as osteoporosis, heart disease, and some cancers. Recent advances in follicle culture (121123) may also provide a way to preserve an ovarian reserve for women undergoing chemotherapy. Information being derived from other new approaches, such as the exponential increase in knowledge of microRNAs, should provide additional insights into the factors, and combined sets of factors, that regulate genes in a cell- and context-specific manner (124128). Finally, advances in ovarian cancer research will continue to be made with mouse models that recapitulate tumors in women, as well as defining criteria for tumor progression (129).

Acknowledgments

This work was supported in part by NIH grants NIH-HD-16229, NIH-HD-16272, and NIH-HD-07945 (Specialized Cooperative Centers Program in Reproduction and Infertility Research) (to J.S. Richards) and by the Burroughs Wellcome Career Award in the Biomedical Sciences, the Dan L. Duncan Cancer Center, and the Caroline Weiss Law Fund for Molecular Medicine (to S.A. Pangas).

Footnotes

Conflict of interest: The authors have declared that no conflict of interest exists.

Citation for this article: J Clin Invest. 2010;120(4):963–972. doi:10.1172/JCI41350.

References

  1. De Felici M, et al. Experimental approaches to the study of primordial germ cell lineage and proliferation. Hum Reprod Update. 2004;10(3):197–206.
    View this article via: PubMed CrossRef
  2. Pesce M, Gioia Klinger F, De Felici M. Derivation in culture of primordial germ cells from cells of the mouse epiblast: phenotypic induction and growth control by Bmp4 signalling. Mech Dev. 2002;112(1-2):15–24.
    View this article via: PubMed CrossRef
  3. Puglisi R, Montanari M, Chiarella P, Stefanini M, Boitani C. Regulatory role of BMP2 and BMP7 in spermatogonia and Sertoli cell proliferation in the immature mouse. Eur J Endocrinol. 2004;151(4):511–520.
    View this article via: PubMed CrossRef
  4. Ross A, Munger S, Capel B. Bmp7 regulates germ cell proliferation in mouse fetal gonads. Sex Dev. 2007;1(2):127–137.
    View this article via: PubMed CrossRef
  5. Martins da Silva SJ, Bayne RA, Cambray N, Hartley PS, McNeilly AS, Anderson RA. Expression of activin subunits and receptors in the developing human ovary: activin A promotes germ cell survival and proliferation before primordial follicle formation. Dev Biol. 2004;266(2):334–345.
    View this article via: PubMed CrossRef
  6. Richards AJ, Enders GC, Resnick JL. Activin and TGFbeta limit murine primordial germ cell proliferation. Dev Biol. 1999;207(2):470–475.
    View this article via: PubMed CrossRef
  7. Yao HH, et al. Follistatin operates downstream of Wnt4 in mammalian ovary organogenesis. Dev Dyn. 2004;230(2):210–215.
    View this article via: PubMed CrossRef
  8. Vainio S, Heikkila M, Kispert A, Chin N, McMahon AP. Female development in mammals is regulated by Wnt-4 signalling. Nature. 1999;397(6718):405–409.
    View this article via: PubMed CrossRef
  9. Parma P, et al. R-spondin1 is essential in sex determination, skin differentiation and malignancy. Nat Genet. 2006;38(11):1304–1309.
    View this article via: PubMed CrossRef
  10. Tomizuka K, et al. R-spondin1 plays an essential role in ovarian development through positively regulating Wnt-4 signaling. Hum Mol Genet. 2008;17(9):1278–1291.
    View this article via: PubMed CrossRef
  11. Ottolenghi C, et al. Loss of Wnt4 and Foxl2 leads to female-to-male sex reversal extending to germ cells. Hum Mol Genet. 2007;16(23):2795–2804.
    View this article via: PubMed CrossRef
  12. Chang H, Gao F, Guillou F, Taketo MM, Huff V, Behringer RR. Wt1 negatively regulates beta-catenin signaling during testis development. Development. 2008;135(10):1875–1885.
    View this article via: PubMed CrossRef
  13. Faddy MJ, Gosden RG, Gougeon A, Richardson SJ, Nelson JF. Accelerated disappearance of ovarian follicles in mid-life: implications for forecasting menopause. Hum Reprod. 1992;7(10):1342–1346.
    View this article via: PubMed
  14. Block E. Quantitative morphological investigations of the follicular system in women; variations at different ages. Acta Anat (Basel). 1952;14(1–2):108–123.
    View this article via: PubMed CrossRef
  15. Baker TG. A Quantitative and Cytological Study of Germ Cells in Human Ovaries. Proc R Soc Lond B Biol Sci. 1963;158:417–433.
    View this article via: PubMed CrossRef
  16. Engle E. Polyovular follicles and polynuclear ova in the mouse. Anat Rec. 1927;35:341–343.
    View this article via: CrossRef
  17. Jagiello G, Ducayen M. Meiosis of ova from polyovular (C58-J) and polycystic (C57 L-J) strains of mice. Fertil Steril. 1973;24(1):10–14.
    View this article via: PubMed
  18. McMullen ML, Cho BN, Yates CJ, Mayo KE. Gonadal pathologies in transgenic mice expressing the rat inhibin alpha-subunit. Endocrinology. 2001;142(11):5005–5014.
    View this article via: PubMed CrossRef
  19. Pangas SA, et al. Intraovarian activins are required for female fertility. Mol Endocrinol. 2007;21(10):2458–2471.
    View this article via: PubMed CrossRef
  20. Yan C, et al. Synergistic roles of bone morphogenetic protein 15 and growth differentiation factor 9 in ovarian function. Mol Endocrinol. 2001;15(6):854–866.
    View this article via: PubMed CrossRef
  21. Hahn KL, Johnson J, Beres BJ, Howard S, Wilson-Rawls J. Lunatic fringe null female mice are infertile due to defects in meiotic maturation. Development. 2005;132(4):817–828.
    View this article via: PubMed CrossRef
  22. Papadaki L. Binovular follicles in the adult human ovary. Fertil Steril. 1978;29(3):342–350.
    View this article via: PubMed
  23. Dandekar PV, Martin MC, Glass RH. Polyovular follicles associated with human in vitro fertilization. Fertil Steril. 1988;49(3):483–486.
    View this article via: PubMed
  24. Balciuniene J, Bardwell VJ, Zarkower D. Mice mutant in the DM domain gene Dmrt4 are viable and fertile but have polyovular follicles. Mol Cell Biol. 2006;26(23):8984–8991.
    View this article via: PubMed CrossRef
  25. Telfer E, Gosden RG. A quantitative cytological study of polyovular follicles in mammalian ovaries with particular reference to the domestic bitch (Canis familiaris). J Reprod Fertil. 1987;81(1):137–147.
    View this article via: PubMed
  26. Kipp JL, Kilen SM, Bristol-Gould S, Woodruff TK, Mayo KE. Neonatal exposure to estrogens suppresses activin expression and signaling in the mouse ovary. Endocrinology. 2007;148(5):1968–1976.
    View this article via: PubMed CrossRef
  27. Iguchi T, Fukazawa Y, Uesugi Y, Takasugi N. Polyovular follicles in mouse ovaries exposed neonatally to diethylstilbestrol in vivo and in vitro. Biol Reprod. 1990;43(3):478–484.
    View this article via: PubMed CrossRef
  28. Iguchi T, Takasugi N. Polyovular follicles in the ovary of immature mice exposed prenatally to diethylstilbestrol. Anat Embryol (Berl). 1986;175(1):53–55.
    View this article via: PubMed
  29. Iguchi T, Takasugi N, Bern HA, Mills KT. Frequent occurrence of polyovular follicles in ovaries of mice exposed neonatally to diethylstilbestrol. Teratology. 1986;34(1):29–35.
    View this article via: PubMed CrossRef
  30. Chen Y, Jefferson WN, Newbold RR, Padilla-Banks E, Pepling ME. Estradiol, progesterone and genistein inhibit oocyte nest breakdown and primordial follicle assembly in the neonatal mouse ovary in vitro and in vivo. Endocrinology. 2007;148(8):3580–3590.
    View this article via: PubMed CrossRef
  31. Jefferson W, Newbold R, Padilla-Banks E, Pepling M. Neonatal genistein treatment alters ovarian differentiation in the mouse: inhibition of oocyte nest breakdown and increased oocyte survival. Biol Reprod. 2006;74(1):161–168.
    View this article via: PubMed CrossRef
  32. Jefferson WN, Couse JF, Padilla-Banks E, Korach KS, Newbold RR. Neonatal exposure to genistein induces estrogen receptor (ER)alpha expression and multioocyte follicles in the maturing mouse ovary: evidence for ERbeta-mediated and nonestrogenic actions. Biol Reprod. 2002;67(4):1285–1296.
    View this article via: PubMed CrossRef
  33. Jefferson WN, Padilla-Banks E, Newbold RR. Adverse effects on female development and reproduction in CD-1 mice following neonatal exposure to the phytoestrogen genistein at environmentally relevant doses. Biol Reprod. 2005;73(4):798–806.
    View this article via: PubMed CrossRef
  34. Jefferson WN, Padilla-Banks E, Newbold RR. Disruption of the developing female reproductive system by phytoestrogens: genistein as an example. Mol Nutr Food Res. 2007;51(7):832–844.
    View this article via: PubMed CrossRef
  35. Nikaido Y, Danbara N, Tsujita-Kyutoku M, Yuri T, Uehara N, Tsubura A. Effects of prepubertal exposure to xenoestrogen on development of estrogen target organs in female CD-1 mice. In Vivo. 2005;19(3):487–494.
    View this article via: PubMed
  36. Jefferson WN, Padilla-Banks E, Goulding EH, Lao SP, Newbold RR, Williams CJ. Neonatal exposure to genistein disrupts ability of female mouse reproductive tract to support preimplantation embryo development and implantation. Biol Reprod. 2009;80(3):425–431.
    View this article via: PubMed CrossRef
  37. Pangas SA, Rajkovic A. Transcriptional regulation of early oogenesis: in search of masters. Hum Reprod Update. 2006;12(1):65–76.
    View this article via: PubMed CrossRef
  38. Liang L-F, Soyal S, Dean J. FIGa, a germ cell specific transcription factor involved in the coordinate expression of the zona pellucida genes. Development. 1997;124(24):4939–4947.
    View this article via: PubMed
  39. Soyal SM, Amleh A, Dean J. FIGa, a germ cell-specific transcription factor required for ovarian follicle formation. Development. 2000;127(21):4645–4654.
    View this article via: PubMed
  40. Choi Y, Yuan D, Rajkovic A. Germ cell-specific transcriptional regulator Sohlh2 is essential for early mouse folliculogenesis and oocyte-specific gene expression. Biol Reprod. 2008;79(6):1176–1182.
    View this article via: PubMed CrossRef
  41. Pangas SA, et al. Oogenesis requires germ cell-specific transcriptional regulators Sohlh1 and Lhx8. Proc Natl Acad Sci U S A. 2006;103(21):8090–8095.
    View this article via: PubMed CrossRef
  42. Choi Y, Rajkovic A. Characterization of NOBOX DNA binding specificity and its regulation of Gdf9 and Pou5f1 promoters. J Biol Chem. 2006;281(47):35747–35756.
    View this article via: PubMed CrossRef
  43. Rajkovic A, Pangas SA, Ballow D, Suzumori N, Matzuk MM. NOBOX deficiency disrupts early folliculogenesis and oocyte-specific gene expression. Science. 2004;305(5687):1157–1159.
    View this article via: PubMed CrossRef
  44. Qin Y, Choi Y, Zhao H, Simpson JL, Chen ZJ, Rajkovic A. NOBOX homeobox mutation causes premature ovarian failure. Am J Hum Genet. 2007;81(3):576–581.
    View this article via: PubMed CrossRef
  45. Zhao H, et al. Transcription factor FIGLA is mutated in patients with premature ovarian failure. Am J Hum Genet. 2008;82(6):1342–1348.
    View this article via: PubMed CrossRef
  46. Uda M, et al. Foxl2 disruption causes mouse ovarian failure by pervasive blockage of follicle development. Hum Mol Genet. 2004;13(11):1171–1181.
    View this article via: PubMed CrossRef
  47. Crisponi L, et al. The putative forkhead transcription factor FOXL2 is mutated in blepharophimosis/ptosis/epicanthus inversus syndrome. Nat Genet. 2001;27(2):159–166.
    View this article via: PubMed CrossRef
  48. Pisarska M, Bae J, Klein C, Hseuh AJ. Forkhead L2 is expressed in the ovary and represses the promoter activity of the steroidogenic acute regulatory gene. Endocrinology. 2004;145(7):3424–3433.
    View this article via: PubMed CrossRef
  49. Uda M, et al. Foxl2 disruption causes mouse ovarian failure by pervasive blockage of follicle development. Human Molecular Genetics. 2004;13(11):1171–1181.
    View this article via: PubMed CrossRef
  50. Moumne L, et al. The mutations and potential targets of the forkhead transcription factor FOXL2. Mol Cell Endocrinol. 2008;282(1-2):2–11.
    View this article via: PubMed CrossRef
  51. Shah SP, et al. Mutation of FOXL2 in granulosa-cell tumors of the ovary. N Engl J Med. 2009;360(26):2719–2729.
    View this article via: PubMed CrossRef
  52. Kalfa N, et al. Aberrant expression of ovary determining gene FOXL2 inn the testis and juvenile granulosa cell tumor in children. Sex Dev. 2008;2(3):142–151.
    View this article via: PubMed CrossRef
  53. Castrillon DH, Miao L, Kollipara R, Horner JW, DePinho RA. Suppression of ovarian follicle activation in mice by the transcription factor Foxo3a. Science. 2003;301(5630):215–218.
    View this article via: PubMed CrossRef
  54. Liu L, et al. Infertility caused by retardation of follicular development in mice with oocyte-specific expression of Foxo3a. Development. 2007;134(1):199–209.
    View this article via: PubMed CrossRef
  55. Reddy P, et al. Oocyte-specific deletion of Pten causes premature activation of the primordial follicle pool. Science. 2008;319(5863):611–613.
    View this article via: PubMed CrossRef
  56. Gallardo TD, et al. Genomewide discovery and classification of candidate ovarian fertility genes in the mouse. Genetics. 2007;177(1):179–194.
    View this article via: PubMed CrossRef
  57. Hosaka T, et al. Disruption of forkhead transcription factor (FOXO) family members in mice reveals their functional diversification. Proc Natl Acad Sci U S A. 2004;101(9):2975–2980.
    View this article via: PubMed CrossRef
  58. Paik JH, et al. FoxOs are lineage-restricted redundant tumor suppressors and regulate endothelial homeostasis. Cell. 2007;128(2):309–323.
    View this article via: PubMed CrossRef
  59. Tothova Z, et al. FoxOs are critical mediators of hematopoetic stem cell resistance to physiologic oxidative stress. Cell. 2007;128(2):325–339.
    View this article via: PubMed CrossRef
  60. Park Y, et al. Induction of cyclin D2 in rat granulosa cells requires FSH-dependent relief from FOXO1 repression coupled with positive signals from Smad. J Biol Chem. 2005;280(10):9135–9148.
    View this article via: PubMed CrossRef
  61. Liu Z, Rudd MD, Hernandez-Gonzalez I, Gonzalez-Robayna I, Zeleznik AJ, Richards JS. Genes in sterol and lipid biosynthetic pathways are targets of FSH and FOXO1 regulation in granulosa cells: evidence from cells expressing mutant forms of FOXO1. [published online ahead of print February 5, 2009].Mol Endocrinol.doi:10.1210/me.2008-0412
    View this article via: CrossRef
  62. Wayne C, Fan HY, Cheng X, Richards JS. FSH induces multiple signaling cascades: evidence that activation of SRC, RAS and EGF receptor impact granulosa cell differentiation. Mol Endocrinol. 2007;21(8):1940–1957.
    View this article via: PubMed CrossRef
  63. Gonzalez-Robayna IJ, Falender AE, Ochsner S, Firestone GL, Richards JS. FSH stimulates phosphorylation and activation of protein kinase B (PKB/Akt) and serum and glucocorticoid-induced kinase (Sgk): evidence for A-kinase independent signaling in granulosa cells. Mol Endocrinol. 2000;14(8):1283–1300.
    View this article via: PubMed CrossRef
  64. Fan HY, Liu Z, Cahill N, Richards JS. Targeted disruption of Pten in ovarian granulosa cells enhances ovulation and extends the life span of luteal cells. Mol Endocrinol. 2008;22(9):2128–2140.
    View this article via: PubMed CrossRef
  65. Hunzicker-Dunn M, Maizels ET. FSH signaling pathways in immature granulosa cells that regulate target gene expression: branching out from protein kinase A. Cell Signal. 2006;18(9):1351–1359.
    View this article via: PubMed CrossRef
  66. Deroo BJ, et al. Estrogen receptor beta is required for optimal cAMP production in mouse granulosa cells. Mol Endocrinol. 2009;23(7):955–965.
    View this article via: PubMed CrossRef
  67. Park Y, et al. Induction of cyclin D2 in rat granulosa cells requires FSH-dependent relief from FOXO1 repression coupled with positive signals from Smad. J Biol Chem. 2005;280(10):9135–9148.
    View this article via: PubMed CrossRef
  68. Parakh TN, et al. Follicle-stimulating hormone/cAMP regulation of aromatase gene expression requires beta-catenin. Proc Natl Acad Sci U S A. 2006;103(33):12435–12440.
    View this article via: PubMed CrossRef
  69. Cross DA, Alessi DR, Cohen P, Andjelkovich M, Hemmings BA. Inhibition of glycogen synthase-3 by insulin mediated by protein kinase B. Nature. 1995;378(6559):785–789.
    View this article via: PubMed CrossRef
  70. Hernandez Gifford JA, Hunzicker-Dunn ME, Nilson JH. Conditional deletion of beta-catenin mediated by Amhr2cre in mice causes female infertility. Biol Reprod. 2009;80(6):1282–1292.
    View this article via: PubMed CrossRef
  71. Boerboom D, et al. Misregulated Wnt/beta-catenin signaling leads to ovarian granulosa cell tumor development. Cancer Res. 2005;65(20):9206–9215.
    View this article via: PubMed CrossRef
  72. Lague MN, et al. Synergistic effects of Pten loss and WNT/CTNNB1 signaling pathway activation in ovarian granulosa cell tumor development and progression. Carcinogenesis. 2008;29(11):2062–2072.
    View this article via: PubMed CrossRef
  73. Fan HY, et al. Selective expression of KrasG12D in granulosa cells of the mouse ovary causes defects in follicular development and ovulation. Development. 2008;135(12):2127–2137.
    View this article via: PubMed CrossRef
  74. Fan HY, et al. Cell type-specific targeted mutations of kras and pten document proliferation arrest in granulosa cells versus oncogenic insult to ovarian surface epithelial cells. Cancer Res. 2009;69(16):6463–6472.
    View this article via: PubMed CrossRef
  75. Pangas S, Matzuk MM. The TGF–B family in the reproductive tract. In: Miyazono DR and K, eds. The TGF–beta family . New York, New York: Cold Spring Harbor Laboratory Press; 2009:861–888.
  76. Jorgez CJ, Klysik M, Jamin SP, Behringer RR, Matzuk MM. Granulosa cell-specific inactivation of follistatin causes female fertility defects. Mol Endocrinol. 2004;18(4):953–967.
    View this article via: PubMed CrossRef
  77. Jeyasuria P, et al. Cell-specific knockout of steroidogenic factor 1 reveals its essential roles in gonadal function. Mol Endocrinol. 2004;18(7):1610–1619.
    View this article via: PubMed CrossRef
  78. Rivier C, Vale W. Effect of recombinant activin-A on gonadotropin secretion in the female rat. Endocrinology. 1991;129(5):2463–2465.
    View this article via: PubMed CrossRef
  79. Rivier C, Rivier J, Vale W. Inhibin-mediated feedback control of follicle-stimulating hormone secretion in the female rat. Science. 1986;234(4773):205–208.
    View this article via: PubMed CrossRef
  80. Woodruff TK, Krummen LA, Lyon RJ, Stocks DL, Mather JP. Recombinant human inhibin A and recombinant human activin A regulate pituitary and ovarian function in the adult female rat. Endocrinology. 1993;132(6):2332–2341.
    View this article via: PubMed CrossRef
  81. Matzuk M, Finegold M, Su J, Hsueh A, Bradley A. a-Inhibin is a tumor-suppressor gene with gonadal specificity in mice. Nature. 1992;360(6402):313–319.
    View this article via: PubMed CrossRef
  82. Matzuk MM, Finegold MJ, Mather JP, Krummen L, Lu H, Bradley A. Development of cancer cachexia-like syndrome and adrenal tumors in inhibin-deficient mice. Proc Natl Acad Sci U S A. 1994;91(19):8817–8821.
    View this article via: PubMed CrossRef
  83. Matzuk MM, et al. Transgenic models to study the roles of inhibins and activins in reproduction, oncogenesis, and development. Recent Prog Horm Res. 1996;51:123–154.
    View this article via: PubMed
  84. Myers M, Middlebrook B, Matzuk MM, Pangas JC. Loss of inhibin alpha uncouples oocyte-granulosa cell dynamics and disrupts postnatal folliculogenesis. Dev Biol. 2009;334(2):458–467.
    View this article via: PubMed CrossRef
  85. Thomas FH, Vanderhyden BC. Oocyte–granulosa cell interactions during mouse follicular development: regulation of kit ligand expression and its role in oocyte growth. Reprod Biol Endocrinol. 2006;4:19.
    View this article via: PubMed CrossRef
  86. Elvin JA, Yan C, Wang P, Nishimori K, Matzuk MM. Molecular characterization of the follicle defects in the growth differentiation factor-9-deficient ovary. Mol Endocrinol. 1999;13(6):1018–1034.
    View this article via: PubMed CrossRef
  87. Matzuk MM, Kumar TR, Bradley A. Different phenotypes for mice deficient in either activins or activin receptor type II. Nature. 1995;374(6520):356–360.
    View this article via: PubMed CrossRef
  88. Vassalli A, Matzuk MM, Gardner H, Lee K, Jaenisch R. Activin/inhibin bB subunit gene disruption leads to defects in eyelid development and female reproduction. Genes Dev. 1994;8(4):414–427.
    View this article via: PubMed CrossRef
  89. Brown CW, Houston-Hawkins DE, Woodruff TK, Matzuk MM. Insertion of Inhbb into the Inhba locus rescues the Inhba-null phenotype and reveals new activin functions. Nat Genet. 2000;25(4):453–457.
    View this article via: PubMed CrossRef
  90. Coerver KA, Woodruff TK, Finegold MJ, Mather J, Bradley A, Matzuk MM. Activin signaling through activin receptor type II causes the cachexia-like symptoms in inhibin-deficient mice. Mol Endocrinol. 1996;10(5):534–543.
    View this article via: PubMed CrossRef
  91. Li Q, Graff JM, O’Connor AE, Loveland KL, Matzuk MM. SMAD3 regulates gonadal tumorigenesis. Mol Endocrinol. 2007;21(10):2472–2486.
    View this article via: PubMed CrossRef
  92. Li Q, et al. Prevention of cachexia-like syndrome development and reduction of tumor progression in inhibin-deficient mice following administration of a chimeric activin receptor type II-murine Fc protein. Mol Hum Reprod. 2007;13(9):675–683.
    View this article via: PubMed CrossRef
  93. Looyenga BD, Hammer GD. Genetic removal of smad3 from inhibin-null mice attenuates tumor progression by uncoupling extracellular mitogenic signals from the cell cycle machinery. Mol Endocrinol. 2007;21(10):2440–2457.
    View this article via: PubMed CrossRef
  94. Li Q, Pangas SA, Jorgez CJ, Graff JM, Weinstein M, Matzuk MM. Redundant Roles of SMAD2 and SMAD3 in Ovarian Granulosa Cells in vivo. Mol Cell Biol. 2008;28(23):7001–7011.
    View this article via: PubMed CrossRef
  95. Pangas SA, Li X, Robertson EJ, Matzuk MM. Premature luteinization and cumulus cell defects in ovarian-specific Smad4 knockout mice. Mol Endocrinol. 2006;20(6):1406–1422.
    View this article via: PubMed CrossRef
  96. Pangas SA, et al. Conditional deletion of Smad1 and Smad5 in somatic cells of male and female gonads leads to metastatic tumor development in mice. Mol Cell Biol. 2008;28(1):248–257.
    View this article via: PubMed CrossRef
  97. Middlebrook BS, Eldin K, Li X, Shivasankaran S, Pangas SA. Smad1-Smad5 ovarian conditional knockout mice develop a disease profile similar to the juvenile form of human granulosa cell tumors. Endocrinology. 2009;150(12):5208–5217.
    View this article via: PubMed CrossRef
  98. Derynck R, Zhang YE. Smad-dependent and Smad-independent pathways in TGF-beta family signalling. Nature. 2003;425(6958):577–584.
    View this article via: PubMed CrossRef
  99. Derynck R, Akhurst RJ, Balmain A. TGF-beta signaling in tumor suppression and cancer progression. Nat Genet. 2001;29(2):117–129.
    View this article via: PubMed CrossRef
  100. Gazzerro E, Canalis E. Bone morphogenetic proteins and their antagonists. Rev Endocr Metab Disord. 2006;7(1–2):51–65.
    View this article via: PubMed CrossRef
  101. Langenfeld EM, Kong Y, Langenfeld J. Bone morphogenetic protein-2-induced transformation involves the activation of mammalian target of rapamycin. Mol Cancer Res. 2005;3(12):679–684.
    View this article via: PubMed CrossRef
  102. Hernandez-Gonzalez I, et al. Gene expression profiles of cumulus cell oocyte complexes during ovulation reveal cumulus cells express neuronal and immune-related genes: does this expand their role in the ovulation process? Mol Endocrinol. 2006;20(6):1300–1321.
    View this article via: PubMed CrossRef
  103. Shimada M, Gonzalez-Robayna I, Hernandez-Gonzalez I, Richards JS. Paracrine and autocrine regulation of EGF-like factors in cumulus oocyte complexes and granulosa cells: key role for prostaglandin synthase 2 (Ptgs2) and progesterone receptor (Pgr). Mol Endocrinol. 2006;20(2):348–364.
    View this article via: PubMed CrossRef
  104. Conti M, Hsieh M, Park J-Y, Su Y-Q. Role of the EGF network in ovarian follicles. Mol Endocrinol. 2005;20(4):715–723.
    View this article via: PubMed CrossRef
  105. Hsieh M, et al. Luteinizing hormone-dependent activation of the epidermal growth factor network is essential for ovulation. Mol Cell Biol. 2007;27(5):1914–1924.
    View this article via: PubMed CrossRef
  106. Fan HY, et al. MAPK3/1 (ERK1/2) in ovarian granulosa cells are essential for female fertility. Science. 2009;324(5929):938–941.
    View this article via: PubMed CrossRef
  107. Bliss SP, et al. ERK signaling in the pituitary is required for female but not male fertility. Mol Endocrinol. 2009;23(7):1092–1101.
    View this article via: PubMed CrossRef
  108. Tullet JMA, Pocock V, Steel JH, White R, Milligan S, Parker MG. Multiple signaling defects in the absence of RIP140 impair both cumulus expansion and follicle rupture. Endocrinology. 2005;146(9):4127–4137.
    View this article via: PubMed CrossRef
  109. Duggavathi R, et al. Liver receptor homolog 1 is essential for ovulation. Genes Dev. 2008;22(14):1871–1876.
    View this article via: PubMed CrossRef
  110. Luo X, Ikeda Y, Parker KL. A cell-specific nuclear receptor is essential for adrenal and gonadal development and sexual differentiation. Cell. 1994;77(4):481–490.
    View this article via: PubMed CrossRef
  111. Pelusi C, Ikeda Y, Zubair M, Parker KL. Impaired Follicle Development and Infertility in Female Mice Lacking Steroidogenic Factor 1 in Ovarian Granulosa Cells. Biol Reprod. 2008;79(6):1074–1083.
    View this article via: PubMed CrossRef
  112. Weck J, Mayo KE. Switching of NR5A proteins associated with the inhibin alpha-subunit gene promoter after activation of the gene in granulosa cells. Mol Endocrinol. 2006;20(5):1090–1103.
    View this article via: PubMed CrossRef
  113. Gershon E, Hourvitz A, Reikhav S, Maman E, Dekel N. Low expression of COX2, reduced cumulus expansion and impaired ovulation in SULT1E1-deficient mice. FASEB J. 2007;21(8):1893–1901.
    View this article via: PubMed CrossRef
  114. Sterneck E, Tassarollo L, Johnson PF. An essential role for C/EBPb in female reproduction. Genes Dev. 1997;11(17):2153–2162.
    View this article via: PubMed CrossRef
  115. Liu Z, deMatos DG, Fan HY, Shimada M, Palmer S, Richards JS. IL6: a potent regulator of the mouse cumulus cells-oocyte complex expansion process. Endocrinology. 2009;150(7):3360–3368.
    View this article via: PubMed CrossRef
  116. Liu Z, Shimada M, Richards JS. The involvement of the Toll-like receptor family in ovulation. J Assist Reprod Genet. 2008;25(6):223–228.
    View this article via: PubMed CrossRef
  117. Richards JS, Liu Z, Shimada M. Immune-like mechanisms in ovulation. Trends Endocrinol Metab. 2008;19(6):191–196.
    View this article via: PubMed CrossRef
  118. Molyneaux KA, Schaible K, Wylie C. GP130, the shared receptor for the LIF/I:6 cytokine family in the mouse, is not required for early germ cell differentiation but is required cell-autonomously in oocytes for ovulation. Development. 2003;130(18):4287–4294.
    View this article via: PubMed CrossRef
  119. Kim J, et al. Peroxisome proliferator-activated receptor gamma is a target of progesterone receptor regulation in preovulatory follicles and controls ovulation in mice. Mol Cell Biol. 2008;28(5):1770–1782.
    View this article via: PubMed CrossRef
  120. Shimada M, et al. Synaptosomal associated protein 25 gene expression is hormonally regulated during ovulation and is involved in cytokine/chemokine exocytosis from granulosa cells. Mol Endocrinol. 2007;21(10):2487–2502.
    View this article via: PubMed CrossRef
  121. Pangas SA, Saudye H, Shea LD, Woodruff TK. Novel approach for the three-dimensional culture of granulosa cell-oocyte complexes. Tissue Eng. 2003;9(5):1013–1021.
    View this article via: PubMed CrossRef
  122. Xu M, Kreeger PK, Shea LD, Woodruff TK. Tissue-engineered follicles produce live, fertile offspring. Tissue Eng. 2006;12(10):2739–2746.
    View this article via: PubMed CrossRef
  123. Amorim CA, Van Langendonckt A, David A, Dolmans MM, Donnez J. Survival of human pre-antral follicles after cryopreservation of ovarian tissue, follicular isolation and in vitro culture in a calcium alginate matrix. Hum Reprod. 2009;24(1):92–99.
    View this article via: PubMed CrossRef
  124. Otsuka M, et al. Impaired microRNA processing causes corpus luteum insufficiency and infertility in mice. J Clin Invest. 2008;118(5):1944–1954.
    View this article via: JCI.org PubMed CrossRef
  125. Nagaraja AK, et al. Deletion of Dicer in somatic cells of the female reproductive tract causes sterility. Mol Endocrinol. 2008;22(10):2336–2352.
    View this article via: PubMed CrossRef
  126. Hong X, Luense LJ, McGinnis LK, Nothnick WB, Christenson LK. Dicer1 Is Essential for Female Fertility and Normal Development of the Female Reproductive System. Endocrinology. 2008;149(12):6207–6213.
    View this article via: PubMed CrossRef
  127. Fiedler SD, Carletti MZ, Hong X, Christenson LK. Hormonal Regulation of MicroRNA Expression in Periovulatory Mouse Mural Granulosa Cells. Biol Reprod. 2008;79(6):1030–1037.
    View this article via: PubMed CrossRef
  128. Mishima T, et al. MicroRNA cloning analis reveals sex differences in microRNa expression profiles between adult mouse testis and ovary. Reproduction. 2008;136(6):811.
    View this article via: PubMed CrossRef
  129. Shih Ie M, Kurman RJ. Ovarian tumorigenesis: a proposed model based on morphological and molecular genetic analysis. Am J Pathol. 2004;164(5):1511–1518.
    View this article via: PubMed
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