Recombinant growth differentiation factor-9 (GDF-9) enhances growth and differentiation of cultured early ovarian follicles

Modifications of human growth differentiation factor 9 to improve the generation of embryos from low competence oocytes

Growth differentiation factor 9 (GDF9) is an oocyte-derived growth factor that plays a critical role in ovarian folliculogenesis and oocyte developmental competence and belongs to the TGF-β family of proteins. Recombinant human GDF9 (hGDF9) is secreted in a latent form, which in the case of the fully processed protein, has the proregion noncovalently associated with the mature region. In this study, we investigated a number of amino acid residues in the mature region of hGDF9 that are different from the corresponding residues in the mouse protein, which is not latent. We designed, expressed, and purified 4 forms of chimeric hGDF9 (M1-M4) that we found to be active in a granulosa cell bioassay. Using a porcine in vitro maturation model with inherent low developmental competence (yielding 10%-20% blastocysts), we tested the ability of the chimeric hGDF9 proteins to improve oocyte maturation and developmental competence. Interestingly, one of the chimeric proteins, M3, was able to significantly increase the level of embryo production using such low competence oocytes. Our molecular modeling studies suggest that in the case of hGDF9 the Gly(391)Arg mutation probably increases receptor binding affinity, thereby creating an active protein for granulosa cells in vitro. However, for an improvement in oocyte developmental competence, a second mutation (Ser(412)Pro), which potentially decreases the affinity of the mature region for the proregion, is also required.

Simulated Microgravity Using a Rotary Culture System Compromises the In Vitro Development of Mouse Preantral Follicles

Background

Growing cells in simulated weightlessness condition might be a highly promising new technique to maintain or generate tissue constructs in a scaffold-free manner. There is limited evidence that microgravity condition may affect development of ovarian follicles. The objective of the present study was to investigate the effects of simulated microgravity on the in vitro development of mouse preantral follicles.

Methods and Results

Ovarian tissue from 14-day-old mice, or preantral follicles mechanically isolated from 14-day-old mouse ovaries were cultured at a simulated microgravity condition generated using a rotating wall vessel apparatus. Follicle survival was assessed quantitatively using H&E staining. Follicle diameter and oocyte diameter were measured under an inverted microscope. Ultrastructure of oocytes was evaluated using transmission electron microscopy. We observed that simulated microgravity compromised follicle survival in vitro, downregulated PCNA and GDF-9 expressions, and caused ultrastructural abnormalities in oocytes.

Conclusion

This study showed for the first time that three-dimensional culture condition generated by simulated microgravity is detrimental to the initial stage development of mouse preantral follicles in vitro. The experimental setup provides a model to further investigate the mechanisms involved in the in vitro developmental processes of oocytes/granulosa cells under the microgravity condition.

Role of Growth Differentiation Factor 9 and Bone Morphogenetic Protein 15 in Ovarian Function and Their Importance in Mammalian Female Fertility - A Review

Growth factors play an important role during early ovarian development and folliculogenesis, since they regulate the migration of germ cells to the gonadal ridge. They also act on follicle recruitment, proliferation/atresia of granulosa cells and theca, steroidogenesis, oocyte maturation, ovulation and luteinization. Among the growth factors, the growth differentiation factor 9 (GDF9) and the bone morphogenetic protein 15 (BMP15), belong to the transforming growth factor beta (TGF-β) superfamily, have been implicated as essential for follicular development. The GDF9 and BMP15 participate in the evolution of the primordial follicle to primary follicle and play an important role in the later stages of follicular development and maturation, increasing the steroidogenic acute regulatory protein expression, plasminogen activator and luteinizing hormone receptor (LHR). These factors are also involved in the interconnections between the oocyte and surrounding cumulus cells, where they regulate absorption of amino acids, glycolysis and biosynthesis of cholesterol cumulus cells. Even though the mode of action has not been fully established, in vitro observations indicate that the factors GDF9 and BMP15 stimulate the growth of ovarian follicles and proliferation of cumulus cells through the induction of mitosis in cells and granulosa and theca expression of genes linked to follicular maturation. Thus, seeking greater understanding of the action of these growth factors on the development of oocytes, the role of GDF9 and BMP15 in ovarian function is summarized in this brief review.

Three dimensional in vitro culture of preantral follicles following slow-freezing and vitrification of mouse ovarian tissue

To evaluate the effects slow-freezing and vitrification on three dimensional in vitro culture of preantral follicles, ovaries of 12-14 days old female NMRI mice were isolated and randomly assigned to fresh control, slow-freezing and vitrification groups. Slow-freezing was performed using programmable freezer. Vitrification was carried out in a medium consisting of ethylene glycol (EG) and dimethyl sulphoxide (Me2SO) by needle immersion method. middle sized preantral follicles were mechanically isolated and cultured for 12 days in 0.7% sodium alginate gel. The follicles development and quantitative expression of oocyte specific genes (Bmp15, Gdf9, Fgf8) and the growth related genes (Igf1, Kit, Kit-l) were assessed after 1, 8 and 12 days of culture. Both cryopreserved groups showed reduction of follicular survival rates compared to the control group on days 8 and 12 of culture (P < 0.05). Antrum formation rates reduced in slow-freezing after 12 days of culture (P < 0.05). Evaluation of gene expression showed reduction of Bmp15, Gdf9, Fgf8, Kit and Kit-l during 12 days of culture (P < 0.05). Kit and Kit-l expression in slow-freezing group significantly reduced on day 8 of culture (p < 0.05). Igf1 expression was lower in slow-freezing group on 1st day of culture than vitrification and control groups (P < 0.05). Finally, intergroup comparison showed same expression pattern of genes after 12 days of culture. Thus, cryopreservation of mouse ovaries by both methods can preserve most developmental parameters and expression of maturation genes. However, vitrification is a better method for cryopreservation of mouse ovaries due to greater antrum formation and expression of growth related markers.

Cooperative Effects of FOXL2 with the Members of TGF-β Superfamily on FSH Receptor mRNA Expression and Granulosa Cell Proliferation from Hen Prehierarchical Follicles

Forkhead box L2 (FOXL2) is a member of the forkhead nuclear factor 3 gene family and plays an essential role in ovarian growth and maturation in mammals. However, its potential effects and regulative mechanism in development of chicken ovarian prehierarchical follicles remain unexplored. In this study, the cooperative effects of FOXL2 with activin A, growth differentiation factor-9 (GDF9) and follistatin, three members of the transforming growth factor beta (TGF-β) superfamily that were previously suggested to exert a critical role in follicle development was investigated. We demonstrated herein, using in-situ hybridization, Northern blot and immunohistochemical analyses of oocytes and granulosa cells in various sizes of prehierarchical follicles that both FOXL2 transcripts and FOXL2 proteins are predominantly expressed in a highly similar expression pattern to that of GDF9 gene. In addition, the FOXL2 transcript was found at lower levels in theca cells in the absence of GDF9. Furthermore, culture of granulosa cells (GCs) from the prehierarchical follicles (6–8 mm) in conditioned medium revealed that in the pcDNA3.0-FOXL2 transfected GCs, there was a more dramatic increase in FSHR mRNA expression after treatment with activin A (10 ng/ml) or GDF9 (100 ng/ml) for 24 h which caused a stimulatory effect on the GC proliferation. In contrast, a significant decrease of FSHR mRNA was detected after treatment with follistatin (50 ng/ml) and resulted in an inhibitory effect on the cell proliferation. The results of this suggested that FOXL2 plays a bidirectional modulating role involved in the intracellular FSHR transcription and GC proliferation via an autocrine regulatory mechanism in a positive or negative manner through cooperation with activin A and/or GDF9, and follistatin in the hen follicle development. This cooperative action may be mediated by the examined Smad signals and simultaneously implicated in modulation of the StAR, CCND2, and CYP11A1 expression.

Calreticulin is required for development of the cumulus oocyte complex and female fertility

Calnexin (CANX) and calreticulin (CALR) chaperones mediate nascent glycoprotein folding in the endoplasmic reticulum. Here we report that these chaperones have distinct roles in male and female fertility. Canx null mice are growth retarded but fertile. Calr null mice die during embryonic development, rendering indeterminate any effect on reproduction. Therefore, we conditionally ablated Calr in male and female germ cells using Stra8 (mcKO) and Zp3 (fcKO) promoter-driven Cre recombinase, respectively. Calr mcKO male mice were fertile, but fcKO female mice were sterile despite normal mating behavior. Strikingly, we found that Calr fcKO female mice had impaired folliculogenesis and decreased ovulatory rates due to defective proliferation of cuboidal granulosa cells. Oocyte-derived, TGF-beta family proteins play a major role in follicular development and molecular analysis revealed that the normal processing of GDF9 and BMP15 was defective in Calr fcKO oocytes. These findings highlight the importance of CALR in female reproduction and demonstrate that compromised CALR function leads to ovarian insufficiency and female infertility.

Effects of Trichostatin A on Cumulus Expansion during Mouse Oocyte Maturation

This study was conducted to investigate the effects of Trichostatin A (TSA) on cumulus expansion during mouse oocyte maturation. TSA treatment inhibited cumulus expansion and significantly reduced the cumulus expansion index (CEI) (p<0.05). To determine the underlying mechanism, the expression levels of several key factors that play crucial roles in cumulus expansion including components of extracellular matrix (ECM) (Has2, Ptgs2, Ptx3, and Tnfaip6) and Growth differentiation factor 9 (GDF9) were measured in control and TSA treated samples by real-time PCR. The effect of TSA on ERK phosphorylation (p-ERK1/2) in cumulus cells and GDF9 protein level in fully grown oocytes (FGOs) were detected by Western blotting. The expression levels of the ECM genes were significantly decreased (p<0.05) by TSA treatment while GDF9 expression did not response to TSA (p>0.05). TSA treatment blocked the activation of ERK1/2 (p<0.05) and had no significant effect on GDF9 protein expression (p>0.05). Collectively, these results suggested that TSA treatment altered ECM gene expression and blocked ERK1/2 activation to inhibit cumulus expansion in the mouse.

Steroid hormones promote bovine oocyte growth and connection with granulosa cells

Many approaches have been investigated for growing oocytes in vitro in mammals. To support oocyte growth in vitro, the culture systems must meet certain conditions for maintaining connections between oocytes and surrounding granulosa cells. The aims of this study were to determine the effects of combinations of 17β-estradiol (E2) and androstenedione (A4) on in vitro growth of bovine oocytes and to determine the number of connections between the oocyte and granulosa cells. Oocyte-granulosa cell complexes (OGCs) collected from early antral follicles (0.4-0.7 mm in diameter) were cultured for 14 days in a medium with different concentrations of E2 and A4, either alone or in combinations. We then assessed the number of transzonal projections (TZPs), which extend from granulosa cells through the zona pellucida to the oolemma. During in vitro growth culture, OGC structures were maintained in the medium with steroid hormones. The mean diameter of oocytes grown in the medium with both E2 and A4 was increased from 95.8 μm to around 120 μm, larger than oocytes grown without steroid hormones (109.9 μm) and similar in size to in vivo fully grown oocytes (119.4 μm) from 4- to 6-mm antral follicles. In subsequent in vitro maturation culture (22 hours), 30% (12 of 40) and 34% (14 of 41) of oocytes grown with E2 or A4 alone, respectively, matured to metaphase II; meanwhile, oocytes grown with a combination of E2 and A4 matured to metaphase II at a high rate (58%, 23 of 40). Growing oocytes isolated from early antral follicles had many uniformly distributed TZPs throughout the zona pellucida. After 14 days of culture, there was a significant decrease in the number of TZPs in oocytes grown without steroid hormones, whereas the number of TZPs was maintained in oocytes grown with steroid hormones. In particular, oocytes grown with E2 alone or with a combination of E2 and A4 had numbers of TZPs similar to oocytes before growth culture. In conclusion, a combination of E2 and A4 maintained the connections between oocytes and granulosa cells during in vitro growth culture of bovine oocytes for 14 days, resulting in the complete oocyte growth and the acquisition of meiotic competence in more than half the oocytes.

Role of oocyte-derived paracrine factors in follicular development

Mammalian oocytes secrete transforming growth factor β (TGF-β) superfamily proteins, such as growth differentiation factor 9 (GDF9), bone morphogenetic protein 6 (BMP6) and BMP15, and fibroblast growth factors (FGFs). These oocyte-derived paracrine factors (ODPFs) play essential roles in regulating the differentiation and function of somatic granulosa cells as well as the development of ovarian follicles. In addition to the importance of individual ODPFs, emerging evidence suggests that the interaction of ODPF signals with other intra-follicular signals, such as estrogen, is critical for folliculogenesis. In this review, we will discuss the current understanding of the role of ODPFs in follicular development with an emphasis on their interaction with estrogen signaling in regulation of the differentiation and function of granulosa cells.

Transforming growth factor-β signaling participates in the maintenance of the primordial follicle pool in the mouse ovary

Physiologically, only a few primordial follicles are activated to enter the growing follicle pool each wave. Recent studies in knock-out mice show that early follicular activation depends on signaling from the tuberous sclerosis complex, the mammalian target of rapamycin complex 1 (mTORC1), phosphatase and tensin homolog deleted on chromosome 10, and phosphatidylinositol 3-kinase (PI3K) pathways. However, the manner in which these pathways are normally regulated, and whether or not TGF-β acts on them are poorly understood. So, this study aims to identify whether or not TGF-β acts on the process. Ovary organ culture experiments showed that the culture of 18.5 days post-coitus (dpc) ovaries with TGF-β1 reduced the total population of oocytes and activated follicles, accelerated oocyte growth was observed in ovaries treated with TGF-βR1 inhibitor 2-(5-chloro-2-fluorophenyl)pteridin-4-yl]pyridin-4-yl-amine (SD208) compared with control ovaries, the down-regulation of TGF-βR1 gene expression also activated early primordial follicle oocyte growth. We further showed that there was dramatically more proliferation of granulosa cells in SD208-treated ovaries and less proliferation in TGF-β1-treated ovaries. Western blot and morphological analyses indicated that TGF-β signaling manipulated primordial follicle growth through tuberous sclerosis complex/mTORC1 signaling in oocytes, and the mTORC1-specific inhibitor rapamycin could partially reverse the stimulated effect of SD208 on the oocyte growth and decreased the numbers of growing follicles. In conclusion, our results suggest that TGF-β signaling plays an important physiological role in the maintenance of the dormant pool of primordial follicles, which functions through activation of p70 S6 kinase 1 (S6K1)/ribosomal protein S6 (rpS6) signaling in mouse ovaries.

Growth differentiation factor 9 of Megalobrama amblycephala: molecular characterization and expression analysis during the development of early embryos and growing ovaries

Growth differentiation factor 9 (GDF9) is a member of the transforming growth factorβ superfamily and plays an essential role during follicle maturation in mammals. In the present study, the full-length complementary DNA (cDNA) of gdf9 was obtained from Megalobrama amblycephala. The cDNA sequence is 2,061 bp in length with an open reading frame of 1,287 bp encoding 428 amino acid residues. The deduced amino acid sequence shared identities of about 42-86 % with the homologues of other vertebrates. During the early development of embryos, the gdf9 mRNA was detected in zygote with significantly high level and declined sharply by 47 and 87 % at 4 hours post-fertilization (hpf) and 6 hpf and even to an undetectable level through advancing stages. Expression analysis based on quantitative real-time PCR revealed that gdf9 mRNA was mainly expressed in ovary, but much lower levels were also found in some nonovarian tissues. Within the follicle, gdf9 mRNA was localized both in the oocytes and the follicle layer cells by in situ hybridization. During the ovarian cycle, gdf9 mRNA significantly decreased after the previtellogenic stage and became to increase again after the fully grown stage. The results imply that Gdf9 may play critical physiological functions in M. amblycephala early embryonic development and reproduction.

Insulin-like 3-induced rat preantral follicular growth is mediated by growth differentiation factor 9

The communication of somatic cells and oocytes by intrafollicular paracrine factors is essential for follicular growth in the ovary. Insulin-like 3 (INSL3) is a theca cell-secreted paracrine factor. Androgens and growth differentiation factor 9 (GDF9), an oocyte-derived growth factor, are essential for follicular development. Using a rat preantral follicle culture model, we examined in the present study the influence of INSL3 on preantral follicular growth and the molecular mechanisms involved. We have observed that the receptor for INSL3, relaxin/insulin-like family peptide receptor 2 (RXFP2), was exclusively expressed in oocytes. Recombinant INSL3 stimulated Gdf9 expression, preantral follicular growth, and testosterone synthesis in vitro. Inhibition of the cAMP/protein kinase A signaling pathway (with cAMP antagonist, 8-bromoadenosine 3',5'-cyclic monophosphorothioate, Rp-isomer) attenuated INSL3-induced Gdf9 expression and preantral follicular growth. Moreover, knocking down Gdf9 expression (with small interfering RNA) or inhibiting GDF9 signaling (with SB431542, an activin receptor-like kinase receptor 5 inhibitor, or specific inhibitor of mothers against decapentaplegic homolog 3) or androgen action (with flutamide, an androgen receptor antagonist) suppressed INSL3-induced preantral follicular growth. In addition, LH and DHT regulated the expression of Insl3 mRNA in preantral follicles. These observations suggest that INSL3 is a key theca cell-derived growth factor for preantral follicle and that its action is mediated by GDF9.

Investigations of TGF-β signaling in preantral follicles of female mice reveal differential roles for bone morphogenetic protein 15

Bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are 2 closely related TGF-β ligands implicated as key regulators of follicle development and fertility. Animals harboring mutations of these factors often exhibit a blockage in follicle development beyond the primary stage and therefore little is known about the role of these ligands during subsequent (preantral) stages. Preantral follicles isolated from immature mice were cultured with combinations of BMP15, GDF9, and activin receptor-like kinase (ALK) inhibitors. Individually, GDF9 and BMP15 promoted follicle growth during the first 24 hours, whereas BMP15 subsequently (48-72 h) caused follicle shrinkage and atresia with increased granulosa cell apoptosis. Inhibition of ALK6 prevented the BMP15-induced reduction in follicle size and under basal conditions promoted a rapid increase in granulosa cell proliferation, suggesting BMP15 signals through ALK6, which in turn acts to restrain follicle growth. In the presence of GDF9, BMP15 no longer promoted atresia and in fact follicle growth was increased significantly more than with either ligand alone. This cooperative effect was accompanied by differential expression of Id1-3, Smad6-7, and Has2 and was blocked by the same ALK5 inhibitor used to block GDF9 signaling. Immunostaining for SMAD2/3 and SMAD1/5/8, representing the 2 main branches of TGF-β signaling, supported the fact that both canonical pathways have the potential to be active in growing follicles, whereas primordial follicles only express SMAD2/3. Overall results highlight differential effects of the 2 main TGF-β signaling pathways during preantral follicle growth.

Development of a serum-free defined system employing growth factors for preantral follicle culture

This study was conducted to evaluate if mouse preantral follicles can yield developmentally competent oocytes following culture in serum-free, defined medium. Donor follicles were obtained from 14-day-old B6CBAF1 mice, and cultured in α-MEM-Glutamax medium. The replacement of fetal bovine serum with knockout serum replacement (KSR) did not significantly reduce follicle growth or oocyte maturation in vitro, although it significantly reduced the development of oocytes after activation. Regardless of the replacement medium, follicle growth was not influenced by the addition of leukemia inhibitory factor (LIF). The addition of 100 ng/ml stem cell factor (SCF) to the KSR-supplemented serum-free medium significantly stimulated follicle development, which further improved blastocyst formation after oocyte activation. On Day 3 of culture, a significant increase in Bmp7 expression was detected in the SCF-containing medium compared with the serum-containing medium, whereas Gdf9 and Amh were increased in the serum-containing medium. A significant increase in estradiol production was detected under serum-free conditions, but minimal progesterone secretion was detected throughout the culture period. In conclusion, serum-free media can be used to optimize ovarian follicle cultures, and the addition of SCF is beneficial for deriving developmentally competent oocytes through follicle culture.

Growth differentiation factor 9:bone morphogenetic protein 15 heterodimers are potent regulators of ovarian functions

The TGF-β superfamily is the largest family of secreted proteins in mammals, and members of the TGF-β family are involved in most developmental and physiological processes. Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), oocyte-secreted paralogs of the TGF-β superfamily, have been shown genetically to control ovarian physiology. Although previous studies found that GDF9 and BMP15 homodimers can modulate ovarian pathways in vitro, the functional species-specific significance of GDF9:BMP15 heterodimers remained unresolved. Therefore, we engineered and produced purified recombinant mouse and human GDF9 and BMP15 homodimers and GDF9:BMP15 heterodimers to compare their molecular characteristics and physiological functions. In mouse granulosa cell and cumulus cell expansion assays, mouse GDF9 and human BMP15 homodimers can up-regulate cumulus expansion-related genes (Ptx3, Has2, and Ptgs2) and promote cumulus expansion in vitro, whereas mouse BMP15 and human GDF9 homodimers are essentially inactive. However, we discovered that mouse GDF9:BMP15 heterodimer is ∼10- to 30-fold more biopotent than mouse GDF9 homodimer, and human GDF9:BMP15 heterodimer is ∼1,000- to 3,000-fold more bioactive than human BMP15 homodimer. We also demonstrate that the heterodimers require the kinase activities of ALK4/5/7 and BMPR2 to activate SMAD2/3 but unexpectedly need ALK6 as a coreceptor in the signaling complex in granulosa cells. Our findings that GDF9:BMP15 heterodimers are the most bioactive ligands in mice and humans compared with homodimers explain many puzzling genetic and physiological data generated during the last two decades and have important implications for improving female fertility in mammals.

Kinetics of GDF9 expression in buffalo oocytes during in vitro maturation and their associated development ability

The capacity of fully grown oocytes to regulate their own microenvironment by secreted paracrine factors contribute to their developmental competence. In spite of growing evidence about the vital role of Growth Differentiation Factor 9 (GDF9) in determination of oocyte developmental competence, there is insufficient information about time dependent behavior of its expression during in vitro maturation (IVM) to have definite understanding about at what time point during IVM it plays most crucial role. The study reports the kinetics of GDF9 expression under four different IVM supplement conditions in buffalo oocytes and their concomitant development rate up to blastocyst. Oocytes matured under an ideal media condition with all supplements and those cultured with only FSH resulted in significantly higher cumulus expansion, nuclear maturation, cleavage and blastocyst rates. GDF9 expression at both mRNA and protein levels at different time points of IVM revealed that magnitude of mRNA abundance at 8h of IVM was most important towards imparting development competence to buffalo oocytes. Appearance of GDF9 protein in maturing oocytes was found asynchronous with mRNA appearance in the time course of IVM suggesting possible posttranscriptional regulation of this gene under dynamic oocyte cumulus cell communication process. Abundance of mature GDF9 protein at 16 h was most consistently related with all oocyte development parameters.

Growth differentiation factor 9 (Gdf9) was localized in the female as well as male germ cells in a protogynous hermaphroditic teleost fish, ricefield eel Monopterus albus

Growth differentiation factor 9 (GDF9) is a member of the transforming growth factor beta (TGFb) superfamily. As an oocyte-derived growth factor, GDF9 plays key roles in regulating follicle development. In the present study, we identified a gdf9 homologue from the ovary of ricefield eel, and analyzed its expression both at the mRNA and protein levels. Ricefield eel Gdf9 showed high homologies with those of other teleosts, especially perciformes fish. RT-PCR analysis revealed that ricefield eel gdf9 was expressed exclusively in the ovary and testis. The mRNA levels of gdf9 in the ovary were increased significantly at the pre-vitellogenic (PV) stage and then decreased significantly along with vitellogenesis. During the natural sex change, expression of ricefield eel gdf9 was peaked at the intersexual stages. The immunoreactivity for Gdf9 was localized exclusively in the cytoplasm of the oocytes in the ovary, particularly the oocytes at early stages, but not in the oogonia. Interestingly, strong immunoreactive signals were also detected in the degenerating oocytes in the intersexual gonad. Furthermore, the Gdf9 immunoreactivity was demonstrated for the first time to be localized in the cytoplasm of spermatogonia and spermatocytes of ricefield eel, a teleost fish. Taken together, the results of present study suggested that Gdf9 may play important roles in the folliculogenesis as well as spermatogenesis in ricefield eels.

Molecular control of oogenesis

Oogenesis is a complex process regulated by a vast number of intra- and extra-ovarian factors. Oogonia, which originate from primordial germ cells, proliferate by mitosis and form primary oocytes that arrest at the prophase stage of the first meiotic division until they are fully-grown. Within primary oocytes, synthesis and accumulation of RNAs and proteins throughout oogenesis are essential for oocyte growth and maturation; and moreover, crucial for developing into a viable embryo after fertilization. Oocyte meiotic and developmental competence is gained in a gradual and sequential manner during folliculogenesis and is related to the fact that the oocyte grows in interaction with its companion somatic cells. Communication between oocyte and its surrounding granulosa cells is vital, both for oocyte development and for granulosa cells differentiation. Oocytes depend on differentiated cumulus cells, which provide them with nutrients and regulatory signals needed to promote oocyte nuclear and cytoplasmic maturation and consequently the acquisition of developmental competence.The purpose of this article is to summarize recent knowledge on the molecular aspects of oogenesis and oocyte maturation, and the crucial role of cumulus-cell interactions, highlighting the valuable contribution of experimental evidences obtained in animal models. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

The relationship between Evi-1 expression and mouse ovarian follicular development

The ecotropic viral integration site-1 (Evi-1) is a transcription factor with two sets of zinc finger domains. It is an important regulator of the transforming growth factor beta superfamily. In the present study, we investigated the spatiotemporal expression patterns of Evi-1 using immunohistochemistry in ovaries from neonatal mice, gonadotropin-induced immature mice and mice in estrous cycle. Positive staining for Evi-1 was detected in the cytoplasm of oocytes. In postnatal mice, a high level of Evi-1 immunostaining was found from day 1 to 6, an intermediate level from day 10 to 16 and a low level on day 23. After gonadotropin treatment, Evi-1 was mainly expressed in small follicles and exhibited a very low level in large antral follicles. During the estrous cycle, the expression of Evi-1 was higher in diestrus and estrus than in proestrus and metestrus. Real-time PCR was performed to examine the relationship between Evi-1 mRNA and ovulation related genes (Ptgs2, Tnfaip6, Has2, Cd44, C1qbp). At 4 h after hCG treatment, Evi-1 mRNA was down-regulated whereas ovulation related genes were up-regulated. Overall, the results indicate that Evi-1 is expressed in a stage-specific manner during ovarian follicular development and may be involved in early follicle development.

Characterization of oocyte-expressed GDF9 gene in buffalo and mapping of its TSS and putative regulatory elements

Summary In spite of emerging evidence about the vital role of GDF9 in determination of oocyte competence, there is insufficient information about its regulation of oocyte-specific expression, particularly in livestock animals. Because of the distinct prominence of buffalo as a dairy animal, the present study was undertaken to isolate and characterize GDF9 cDNA using orthologous primers based on the bovine GDF9 sequence. GDF9 transcripts were found to be expressed in oocytes irrespective of their follicular origin, and shared a single transcription start site (TSS) at -57 base pairs (bp) upstream of ATG. Assignment of the TSS is consistent with the presence of a TATA element at -23 of the TSS mapped in this study. Localization of a buffalo-specific minimal promoter within 320 bp upstream of ATG was consolidated by identification of an E-box element at -113bp. Presence of putative transcription factor binding sites and other cis regulatory elements were analyzed at ~5 kb upstream of TSS. Various germ cell-specific cis-acting regulatory elements (BNCF, BRNF, NR2F, SORY, Foxh1, OCT1, LHXF etc.) have been identified in the 5' flanking region of the buffalo GDF9 gene, including NOBOX DNA binding elements and consensuses E-boxes (CANNTG). Presence of two conserved E-boxes found on buffalo sequence at -520 and -718 positions deserves attention in view of its sequence deviation from other species. Two NOBOX binding elements (NBE) were detected at the -3471 and -203 positions. The fall of the NBE within the putative minimal promoter territory of buffalo GDF9 and its unique non-core binding sequence could have a possible role in the control of the core promoter activity.

Xenobiotic effects on ovarian preantral follicles

Women are born with a finite population of ovarian follicles, which are slowly depleted during their reproductive years until reproductive failure (menopause) occurs. The rate of loss of primordial follicles is determined by genetic and environmental influences, but certain toxic exposures can accelerate this process. Ionizing radiation reduces preantral follicle numbers in rodents and humans in a dose-dependent manner. Cigarette smoking is linked to menopause occurring 1-4 yr earlier than with nonsmokers, and components of smoke, polycyclic aromatic hydrocarbons, can cause follicle depletion in rodents or in ovaries in vitro. Chemotherapeutic agents, such as alkylating drugs and cisplatin, also cause loss of preantral ovarian follicles. Effects depend on dose, type, and reactivity of the drug, and the age of the individual. Evidence suggests DNA damage may underlie follicle loss induced by one common alkylating drug, cyclophosphamide. Occupational exposures have also been linked to ovarian damage. In an industrial setting, 2-bromopropane caused infertility in men and women, and it can induce ovarian follicle depletion in rats. Solvents, such as butadiene, 4-vinylcyclohexene, and their diepoxides, can also cause specific preantral follicle depletion. The mechanism(s) underlying effects of the latter compound may involve alterations in apoptosis, survival factors such as KIT/Kit Ligand, and/or the cellular signaling that maintains primordial follicle dormancy. Estrogenic endocrine disruptors may alter follicle formation/development and impair fertility or normal development of offspring. Thus, specific exposures are known or suspected of detrimentally impacting preantral ovarian follicles, leading to early ovarian failure.

Transforming growth factor β receptor type 1 is essential for female reproductive tract integrity and function

The transforming growth factor β (TGFβ) superfamily proteins are principle regulators of numerous biological functions. Although recent studies have gained tremendous insights into this growth factor family in female reproduction, the functions of the receptors in vivo remain poorly defined. TGFβ type 1 receptor (TGFBR1), also known as activin receptor-like kinase 5, is the major type 1 receptor for TGFβ ligands. Tgfbr1 null mice die embryonically, precluding functional characterization of TGFBR1 postnatally. To study TGFBR1–mediated signaling in female reproduction, we generated a mouse model with conditional knockout (cKO) of Tgfbr1 in the female reproductive tract using anti-Müllerian hormone receptor type 2 promoter-driven Cre recombinase. We found that Tgfbr1 cKO females are sterile. However, unlike its role in growth differentiation factor 9 (GDF9) signaling in vitro, TGFBR1 seems to be dispensable for GDF9 signaling in vivo. Strikingly, we discovered that the Tgfbr1 cKO females develop oviductal diverticula, which impair embryo development and transit of embryos to the uterus. Molecular analysis further demonstrated the dysregulation of several cell differentiation and migration genes (e.g., Krt12, Ace2, and MyoR) that are potentially associated with female reproductive tract development. Moreover, defective smooth muscle development was also revealed in the uteri of the Tgfbr1 cKO mice. Thus, TGFBR1 is required for female reproductive tract integrity and function, and disruption of TGFBR1–mediated signaling leads to catastrophic structural and functional consequences in the oviduct and uterus.

Approximately 20% of infertile couples in the United States have unexplained causes. Many vital aspects of female fertility are regulated by a family of growth factors called the transforming growth factor β (TGFβ) superfamily. These factors exert their functions via specific receptors and downstream signal mediators. Perturbation of components in this pathway can lead to reproductive dysfunction. We identified a novel role for a TGFβ receptor (called TGFBR1) in female fertility. We demonstrated that female mice with disruption of Tgfbr1 in the reproductive tract are unable to successfully conceive, although they can ovulate and produce fertilizable oocytes. Most importantly, these mice have a striking deformity in the oviduct, marked by the formation of oviductal outpouchings (diverticula) that prevent embryos from reaching the uterus. Concomitant aberrations in the uterine smooth muscle layers are additional features of mice lacking TGFBR1. Therefore, TGFBR1 is critical for the structural integrity and function of the female reproductive tract. Our model can be further exploited to study the development of smooth muscle cells of the female reproductive tract. Genetic mutations in TGFBR1 or other TGFβ signaling machinery may lead to fertility defects in women.

Growth differentiation factor 9 (GDF9) suppresses follistatin and follistatin-like 3 production in human granulosa-lutein cells

Background

We have demonstrated that growth differentiation factor 9 (GDF9) enhances activin A-induced inhibin β_B-subunit mRNA levels in human granulosa-lutein (hGL) cells by regulating receptors and key intracellular components of the activin signaling pathway. However, we could not exclude its effects on follistatin (FST) and follistatin-like 3 (FSTL3), well recognized extracellular inhibitors of activin A.

Methodology

hGL cells from women undergoing in vitro fertilization (IVF) treatment were cultured with and without siRNA transfection of FST, FSTL3 or GDF9 and then treated with GDF9, activin A, FST, FSTL3 or combinations. FST, FSTL3 and inhibin β_B-subunit mRNA, and FST, FSTL3 and inhibin B protein levels were assessed with real-time RT-PCR and ELISA, respectively. Data were log transformed before ANOVA followed by Tukey's test.

Principal Findings

GDF9 suppressed basal FST and FSTL3 mRNA and protein levels in a time- and dose-dependent manner and inhibited activin A-induced FST and FSTL3 mRNA and protein expression, effects attenuated by BMPR2 extracellular domain (BMPR2 ECD), a GDF9 antagonist. After GDF9 siRNA transfection, basal and activin A-induced FST and FSTL3 mRNA and protein levels increased, but changes were reversed by adding GDF9. Reduced endogenous FST or FSTL3 expression with corresponding siRNA transfection augmented activin A-induced inhibin β_B-subunit mRNA levels as well as inhibin B levels (P values all <0.05). Furthermore, the enhancing effects of GDF9 in activin A-induced inhibin β_B-subunit mRNA and inhibin B production were attenuated by adding FST.

Conclusion

GDF9 decreases basal and activin A-induced FST and FSTL3 expression, and this explains, in part, its enhancing effects on activin A-induced inhibin β_B-subunit mRNA expression and inhibin B production in hGL cells.

Oocyte growth in vitro: potential model for studies of oocyte-granulosa cell interactions

Various factors such as gonadotrophins, growth factors, and steroid hormones play important roles in the regulation of oocyte/follicular growth in mammalian ovaries. In addition to these factors, there is a bidirectional interaction between oocytes and granulosa cells that is essential for achieving optimal oocyte developmental competence. Oocytes play a key role in this interaction by secreting paracrine factors that alter the activities of neighboring cumulus cells, such as the expression of a specific amino acid transporter, cholesterol biosynthesis, and levels of glycolysis in the cumulus cells. Among the known oocyte-derived factors, growth differentiation factor 9 (GDF9) is the dominant factor mediating the regulation by oocytes leading to cumulus expansion and granulosa cell proliferation. GDF9 frequently interacts with other oocyte-derived factors in a synergistic manner. It seems reasonable to speculate that oocytes growing in vitro require interactions similar to those in vivo. Some of the oocyte-mediated regulations have been confirmed in vitro, providing evidence of the usefulness of culture systems as a strong tool for such studies. This review discusses in vitro culture of growing oocytes in terms of oocyte-granulosa cell interactions.

Influence of follicular fluid GDF9 and BMP15 on embryo quality

OBJECTIVE

To evaluate the association between follicular fluid levels of propeptide and mature forms of growth differentiation factor (GDF) 9 and bone morphogenetic protein (BMP) 15 with subsequent oocyte and embryo quality.

DESIGN

Prospective clinical study.

SETTING

University hospital.

PATIENT(S)

Eighty-one infertile patients who underwent in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI).

INTERVENTION(S)

The expression levels of the propeptide and mature forms of follicular fluid GDF9 and BMP15 were determined by western blot analysis. The levels of follicular fluid hormones (FSH, E2, and P) were measured with automated chemiluminescent enzyme immunoassays.

MAIN OUTCOME MEASURE(S)

The relationships between the levels of GDF9 and BMP15, hormones, oocyte maturation, and embryo quality.

RESULT(S)

Mature GDF9 levels were significantly correlated with the nuclear maturation of oocytes. The mean mature GDF9 level was 4.87±0.60 in the high-embryo-quality group and 1.45±0.81 in the low-embryo-quality group. There were no statistically significant differences in embryo quality among the patients regarding propeptide GDF9 and BMP15 expression status. There was a negative correlation between follicular fluid levels of P and the mature form of GDF9.

CONCLUSION(S)

Higher mature GDF9 levels in the follicular fluid were significantly correlated with oocyte nuclear maturation and embryo quality.

Quantitative analysis of bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) gene expression in calf and adult bovine ovaries

BACKGROUND

It has been reported that calf oocytes are less developmentally competent than oocytes obtained from adult cows. Bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9) play critical roles in folliculogenesis, follicular development and ovulation in mammalian ovaries. In the present study, we attempted to compare the expression patterns of BMP15 and GDF9 in the cells of calf and cow ovaries to determine a relationship between the level of these genes and the low developmental competence of calf oocytes.

METHODS

Bovine tissues were collected from 9-11 months-old calves and from 4-6 years-old cows. We characterized the gene expression of BMP15 and GDF9 in calf and adult bovine oocytes and cumulus cells using quantitative real-time reverse transcriptase polymerase chain reaction (QPCR) and in situ hybridization. Immunohistochemical analysis was also performed.

RESULTS

The expression of BMP15 and GDF9 in cumulus cells of adult ovaries was significantly higher than that in calf ovaries, as revealed by QPCR. GDF9 expression in the oocytes of calf ovaries was significantly higher than in those of the adult ovaries. In contrast, BMP15 expression in the oocytes of calf and adult ovaries was not significantly different. The localization of gene expression and protein were ascertained by histochemistry.

CONCLUSIONS

Our result showed for the first time BMP15 and GDF9 expression in bovine cumulus cells. BMP15 and GDF9 mRNA expression in oocytes and cumulus cells was different in calves and cows.

The bioactivity of human bone morphogenetic protein-15 is sensitive to C-terminal modification: characterization of the purified untagged processed mature region

Oocyte-derived bone morphogenetic protein-15 (BMP15) is critical for the regulation of mammalian fertility. Previously we have found that a C-terminal His(6)-tag destroys the bioactivity of growth differentiation-9 (GDF9, a homolog of BMP15). In this study we found that recombinant human BMP15 is produced by HEK-293T cells in an active form, but the bioactivity is lost by C-terminal modification, specifically, fusion to a Flag tag. After purification the mature BMP15 wt is active in transcriptional reporter assays specific for Smad1/5/8 in human granulosa-luteal (hGL) and COV434 granulosa tumor cells, whereas BMP15 with a carboxy-terminal Flag tag remains inactive. Using these same cell models we found that treatment with purified mature BMP15 wt causes a rapid phosphorylation of Smad1. The purified BMP15 wt is a potent stimulator of rat granulosa cell DNA synthesis, which could be antagonized by the BMPRII ectodomain-Fc fusion molecule, whereas the BMP15C-Flag was completely inactive. Further, the BMP15 wt form is a potent stimulator of inhibin B production in hGL cells. We found that the purified BMP15 wt consists of P16 and -17, both of which are post-translationally modified forms. This is the first characterization of a purified untagged human BMP15 mature region, which is stable and highly bioactive in human and rodent granulosa cells and as such is of importance for studies on human fertility.

Integral role of GDF-9 and BMP-15 in ovarian function

The oocyte plays an important role in regulating and promoting follicle growth, and thereby its own development, by the production of oocyte growth factors that predominantly act on supporting granulosa cells via paracrine signaling. Genetic studies in mice demonstrated critical roles of two key oocyte-derived growth factors belonging to the transforming growth factor-β (TGF-β) superfamily, growth and differentiation factor-9 (GDF-9) and bone morphogenetic protein-15 (BMP-15), in ovarian function. The identification of Bmp15 and Gdf9 gene mutations as the causal mechanism underlying the highly prolific or infertile nature of several sheep strains in a dosage-sensitive manner also highlighted the crucial role these two genes play in ovarian function. Similarly, large numbers of mutations in the GDF9 and BMP15 genes have been identified in women with premature ovarian failure and in mothers of dizygotic twins. The purpose of this article is to review the genetic studies of GDF-9 and BMP-15 mutations identified in women and sheep, as well as describing the various knockout and overexpressing mouse models, and to summarize the molecular and biological functions that underlie the crucial role of these two oocyte factors in female fertility.

In vitro culture of sheep lamb ovarian cortical tissue in a sequential culture medium

PURPOSE

This study evaluates the effect of a sequential culture system on the follicular development of sheep lamb ovaries, aiming to establish an available in vitro culture system for ovarian culture.

METHODS

Lamb ovarian cortical fragments were cultured on a steel mesh with a nitrocellulose membrane pre-coated by type 1 collagen. Several culture media were used for the determinations, specifically, a control medium (alpha-MEM), a constant medium (control medium supplemented with 75 ng/mL human recombinant EGF, 200 mIU/mL sheep FSH, 100 ng/mL human recombinant GDF-9, and 100 ng/mL human recombinant bFGF), and a sequential medium (control medium supplemented with sequential growth factors added on different days). Ovarian tissues, both fresh and cultured, were processed for histological and apoptotic assays, while spent culture media were processed for hormone assays.

RESULTS

It was found that the growth of lamb primordial follicles can be initiated during culture in vitro. Compared to the control medium, sequential culture medium significantly increased the percentage of secondary follicles in cultures, while the follicle and oocyte diameters of primary and secondary follicles were also observed to increase in this medium. The constant medium was found to increase the number and diameter of secondary follicles only 18 days after culture. After this same period of time, some normal antral follicles were found in the sequential medium, while a few abnormal antral-like follicles were found in the control medium. Moreover, sequential medium appeared to significantly increase estradiol and inhibin production, especially 10-18 days after culture. The highest percentage of normal follicles and the lowest apoptotic cell rates were observed in the sequential medium, suggesting that a sequential addition style of culture can improve follicle and tissue viability.

CONCLUSIONS

The sequential addition of FSH, EGF, GDF-9,and bFGF can stimulate primordial follicle transmittal into the later development stages, even as far as the antral stage, improve the survival rate of follicles, and maintain follicular viability.

Growth differentiation factor 9 signaling requires ERK1/2 activity in mouse granulosa and cumulus cells

Ovarian folliculogenesis is driven by the combined action of endocrine cues and paracrine factors. The oocyte secretes powerful mitogens, such as growth differentiation factor 9 (GDF9), that regulate granulosa cell proliferation, metabolism, steroidogenesis and differentiation. This study investigated the role of the epidermal growth factor receptor (EGFR)-extracellular signal-regulated kinase 1 and 2 (ERK1/2; also known as MAPK3/1) signaling pathway on GDF9 action on granulosa cells. Results show that mitogenic action of the oocyte is prevented by pharmacological inhibition of the EGFR-ERK1/2 pathway. Importantly, EGFR-ERK1/2 activity as well as rous sarcoma oncogene family kinases (SFK) are required for signaling through SMADs, mediating GDF9, activin A and TGFbeta1 mitogenic action in granulosa cells. GDF9 could not activate ERK1/2 or affect EGF-stimulated ERK1/2 in granulosa cells. However, induction of the SMAD3-specific CAGA reporter by GDF9 in granulosa cells required active EGFR, SFKs and ERK1/2 as did GDF9-responsive gene expression. Finally, the EGFR-SFKs-ERK1/2 pathway was shown to be required for the maintenance of phosphorylation of the SMAD3 linker region. Together our results suggest that receptivity of granulosa cells to oocyte-secreted factors, including GDF9, is regulated by the level of activation of the EGFR and resulting ERK1/2 activity, through the requisite permissive phosphorylation of SMAD3 in the linker region. Our results indicate that oocyte-secreted TGFbeta-like ligands and EGFR-ERK1/2 signaling are cooperatively required for the unique granulosa cell response to the signal from oocytes mediating granulosa cell survival and proliferation and hence the promotion of follicle growth and ovulation.

Stability of housekeeping genes and expression of locally produced growth factors and hormone receptors in goat preantral follicles

The aim of the present study was to investigate the stability of six housekeeping genes, and the relative expression of growth factors (EGF, GDF-9, BMP-15, VEGF, FGF-2, BMP-6, IGF-1 and KL) and hormone receptors (FSH, LH and GH) in goat preantral follicles. To evaluate to stability of housekeeping genes micro-dissected fresh follicles (150–200 μm) as well as follicles that have been in vitro cultured for 12 days were used. In addition, isolated fresh follicles were used to compare expression of various growth factors and hormone receptors before culture. Both fresh and cultured follicles were subjected to total RNA extraction and synthesis of cDNA. After amplification of cDNA by real-time PCR, the geNorm software program was used to evaluate the stability of glyceraldehyde-2-phosphate dehydrogenase (GAPDH), β-tubulin, β-actin, phosphoglycerokinase (PGK), 18S rRNA, ubiquitin (UBQ) and ribosomal protein 19 (RPL-19). In addition, follicular steady-state levels of mRNA from the various growth factors under study were compared. Results demonstrated that, in goat preantral follicles, UBQ and β-actin were the most suitable reference genes and thus could be used as parameters to normalize data from future in vitro studies. In contrast, 18S RNA appeared the least stable gene among the tested housekeeping genes. Analysis of mRNA for several hypophyseal hormone receptors in fresh preantral follicles showed significantly higher FSH-R mRNA levels than those of LH-R and GH-R, and no difference between GH-R and LH-R mRNA levels. In regard growth factor mRNA expression in goat preantral follicles, EGF mRNA levels appeared significantly lower than those of the other studied growth factors. Increasingly higher relative mRNA levels were observed for GDF-9, BMP-15, BMP-6, FGF-2, VEGF, Kl and IGF-1, successively. In conclusion, UBQ and β-actin are the most stable housekeeping genes in fresh and 12-days cultured caprine preantral follicles. Furthermore, in fresh follicles, high levels of FSH-R mRNA are detected while among eight growth factors, IGF-1 is the most highly expressed and EGF the weakest expressed compound.

Steady-state level of kit ligand mRNA in goat ovaries and the role of kit ligand in preantral follicle survival and growth in vitro

The aims of this study were to investigate steady-state level of Kit Ligand (KL) mRNA and its effects on in vitro survival and growth of caprine preantral follicles. RT-PCR was used to analyze caprine steady-state level of KL mRNA in primordial, primary, and secondary follicles, and in small (1-3 mm) and large (3-6 mm) antral follicles. Furthermore, ovarian fragments were cultured for 1 or 7 days in Minimal Essential Medium (MEM(+)) supplemented with KL (0, 1, 10, 50, 100, or 200 ng/ml). Noncultured (control) and cultured fragments were processed for histology and transmission electron microscopy (TEM). RT-PCR demonstrated an increase in steady-state level of KL mRNA during the transition from primary to secondary follicles. Small antral follicles had higher steady-state levels of KL mRNA in granulosa and theca cells than large follicles. After 7 days, only 50 ng/ml of KL had maintained the percentage of normal follicles similar to control. After 1 day, all KL concentrations reduced the percentage of primordial follicles and increased the percentage of growing follicles. KL at 10, 50, 100, or 200 ng/ml increased primary follicles, compared to MEM(+) after 7 days. An increase in oocyte and follicular diameter was observed at 50 ng/ml of KL. TEM confirmed ultrastructural integrity of follicles after 7 days at 50 ng/ml of KL. In conclusion, the KL mRNAs were detected in all follicular categories. Furthermore, 50 ng/ml of KL maintained the integrity of caprine preantral follicle cultured for 7 days and stimulated primordial follicle activation and follicle growth.

Human ovarian follicular development: from activation of resting follicles to preovulatory maturation

By integrating morphometrical and endocrinological data, as well as biological effects of various molecules synthesized by the human follicle, we propose a dynamic view of the follicle growth within the human ovary. Folliculogenesis starts with entry of resting follicles into the growth phase, a process where the kit system plays a key role. Several months are required for a new growing follicle to reach the preantral stage (0.15mm), then 70 additional days to reach the size of 2mm. Early growing follicle growth is regulated by subtle interactions between follicle-stimulating hormone (FSH) and local factors produced by theca and granulosa cells (GCs), as well as the oocyte. From the time they enter the selectable stage during the late luteal phase, follicles become sensitive to cyclic changes of FSH in terms of granulosa cell proliferation. During the early follicular phase, the early selected follicle grows very quickly and estradiol is present in the follicular fluid. However, the total steroid production remains moderate. From the mid-follicular phase, the preovulatory follicle synthesizes high quantities of estradiol, then after the mid-cycle gonadotropin surge, very large amounts of progesterone. At this stage of development, the responsiveness of the follicle to gonadotropins is maximum, especially to luteinizing hormone (LH) that triggers granulosa wall dissociation and cumulus expansion as well as oocyte nuclear maturation. Thus, as the follicle develops, its responsiveness to gonadotropins progressively increases under the control of local factors acting in an autocrine/paracrine fashion.

Bidirectional communication between oocytes and follicle cells: ensuring oocyte developmental competence

Female fertility is determined to a large extent by the quality (developmental competence) of the oocyte as reflected in its ability to undergo meiosis, be fertilized, and give rise to a healthy embryo. Growth of the mammalian oocyte is coordinated with that of the follicle that encloses it by the actions of signals that pass in both directions between the germline and somatic components. This review summarizes what is known about the roles played by 2 different modes of intrafollicular signalling in oogenesis: paracrine factors activating receptors on the opposite cell type, and direct sharing of small molecules throughout the follicle via gap junction channels. Recent evidence indicates that these 2 modes of signalling interact to regulate oocyte growth and granulosa cell proliferation and that defects in either can contribute to female infertility.

Growth differentiation factor-9 mediates follicle-stimulating hormone-thyroid hormone interaction in the regulation of rat preantral follicular development

FSH regulates follicular growth in a stage-development fashion. Although preantral follicle stage is gonadotropin responsive, FSH is not required for preantral follicular growth. With the antrum, the follicles continue growing under the influence of FSH and become gonadotropin dependent. Although thyroid hormone is important for normal female reproductive function, its role and interaction with FSH in the regulation of preantral ovarian follicular growth is yet to be defined. In the present study, we have examined the action and interaction of FSH and T(3) in the regulation of the growth of preantral follicles, especially in their transition from preantral to early antral stage, using an established follicle culture system and evaluated the involvement of growth differentiation factor-9 (GDF-9) in this process in vitro. We have demonstrated that although T(3) alone had no effect on follicular development, it markedly enhanced FSH-induced preantral follicular growth. Although FSH alone significantly down-regulated FSH receptor (FSHR) mRNA abundance in the preantral follicles and T(3) alone was ineffective, expression of the message was significantly increased in the presence of both hormones. In addition, intra-oocyte injection of GDF-9 antisense oligonucleotides (GDF-9 morpholino) induced follicular cell apoptosis and suppressed follicular growth induced by FSH and T(3). These responses were attenuated by exogenous GDF-9. Our findings support the concept that thyroid hormone regulates ovarian follicular development through its direct action on the ovary and that promotes FSH-induced preantral follicular growth through up-regulation of FSHR, a mechanism dependent on the expression and action of oocyte-derived GDF-9.

Dynamic oxygen enhances oocyte maturation in long-term follicle culture

Traditionally, follicles have been grown in standard incubators with atmospheric oxygen concentration. However, preantral follicles exist in the avascular cortex of the ovary. This study examines the effectiveness of an oxygen delivery protocol that more closely mimics the in vivo environment of the ovary on oocyte viability, maturation, parthenogenetic activation, and fertilization from in vitro cultured rat preantral follicles. Of 54 oocytes cultured in the dynamic oxygen environment, 35 were viable while only 22 of 50 oocytes cultured within an ambient oxygen concentration remained viable (p < 0.05). Germinal vesicle breakdown was observed in 56% of oocytes from the dynamic oxygen group compared to 30% of oocytes from the ambient oxygen group (p < 0.05). Parthenogenetic activation was observed in a significant number of oocytes from the dynamic oxygen group, while none of the oocytes from the ambient oxygen group activated (p < 0.05). However, the proportions of oocytes from the dynamic oxygen group that remained viable underwent germinal vesicle breakdown, and activated were still significantly less than those from the in vivo control group (p < 0.05). Fertilization of the oocytes from the dynamic oxygen group was confirmed through a successful trial of intracytoplasmic sperm injection.

Gonadotropin stimulation increases the expression of angiotensin-(1--7) and MAS receptor in the rat ovary

We have previously shown the presence of immunoreactive angiotensin-(1–7) [Ang-(1–7)] in rat ovary homogenate and its stimulatory effect on estradiol and progesterone production in vitro. In the current study, we investigated the presence and cellular distribution of Ang-(1–7) and the Mas receptor, the expression of Mas and angiotensin-converting enzyme 2 (ACE2) messenger RNA (mRNA), and the enzymatic activity in the rat ovary following gonadotropin stimulation in vivo. Immature female Wistar rats (25 days old) were injected subcutaneously (SC) with equine chorionic gonadotropin (eCG, 20 IU in 0.2 mL) or vehicle 48 hours before euthanasia. Tissue distributions of Ang-(1–7), Mas receptor, and ACE2 were evaluated by immunohistochemistry, along with angiotensin II (Ang II) localization, while the mRNA expression levels of Mas receptor and ACE2 were evaluated by real-time polymerase chain reaction (PCR). In addition, we determined the activity of neutral endopeptidase (NEP), prolyl endopeptidase (PEP), and ACE by fluorometric assays. After eCG treatment, we found strong immunoreactivity for Ang-(1–7) and Mas primarily in the theca-interstitial cells, while Ang II appeared in the granulosa but not in the thecal layer. Equine chorionic gonadotropin treatment increased Mas and ACE2 mRNA expression compared with control animals (3.3- and 2.1-fold increase, respectively; P < .05). Angiotensin-converting enzyme and NEP activities were lower, while PEP activity was higher in the eCG-treated rats (P < .05). These data show gonadotropin-induced changes in the ovarian expression of Ang-(1–7), Mas receptor, and ACE2. These findings suggest that the renin-angiotensin system (RAS) branch formed by ACE2/Ang-(1–7)/Mas, fully expressed in the rat ovary and regulated by gonadotropic hormones, could play a role in the ovarian physiology.

Pertinence of apoptosis markers for the improvement of in vitro fertilization (IVF)

In assisted reproductive technology (ART), the pregnancy and birth rates following in vitro fertilization (IVF) attempts are still low. Recently, apoptotic markers have been suggested as new criteria for oocyte and embryo quality selection. Many studies have provided evidence that poor oocyte and embryo quality can be associated with apoptosis. The aim of this review is to summarize our current knowledge on the apoptotic process in oocytes and embryos, and focus on the possibility for using apoptotic markers as a reliable and predictive marker to select competent oocytes and embryos during IVF. Moreover, it is currently accepted that IVF failures, linked to poor embryo quality, are, in part, associated with suboptimal in vitro culture conditions. Here, we also review the current state of knowledge concerning how the genetic control of apoptosis during folliculogenesis and pre-implantation embryonic development is affected by in vitro culture conditions during IVF. In the future, identification of apoptotic markers in ART for oocyte and embryo selection should result in the development of new agonistic or antagonistic molecules of apoptosis by medicinal chemistry.

Oocyte-granulosa-theca cell interactions during preantral follicular development

The preantral-early antral follicle transition is the penultimate stage of follicular development in terms of gonadotropin dependence and follicle destiny (growth versus atresia). Follicular growth during this period is tightly regulated by oocyte-granulosa-theca cell interactions. Formation of the theca cell layer is a key event that occurs during this transitional stage. Granulosal factor(s) stimulates the recruitment of theca cells from cortical stromal cells, while oocyte-derived growth differentiation factor-9 (GDF-9) is involved in the differentiation of theca cells during this early stage of follicular development. The preantral to early antral transition is most susceptible to follicular atresia. GDF-9 promotes follicular survival and growth during transition from preantral stage to early antral stage by suppressing granulosa cell apoptosis and follicular atresia. GDF-9 also enhances preantral follicle growth by up-regulating theca cell androgen production. Thecal factor(s) promotes granulosa cell proliferation and suppress granulosa cell apoptosis. Understanding the intraovarian mechanisms in the regulation of follicular growth and atresia during this stage may be of clinical significance in the selection of the best quality germ cells for assisted reproduction. In addition, since certain ovarian dysfunctions, such as polycystic ovarian syndrome and gonadotropin poor-responsiveness, are consequences of dysregulated follicle growth at this transitional stage, understanding the molecular and cellular mechanisms in the control of follicular development during the preantral-early antral transition may provide important insight into the pathophysiology and rational treatment of these conditions.