Ovarian follicle development and transgenic mouse models

Oocytes lacking O-glycans alter follicle development and increase fertility by increasing follicle FSH sensitivity, decreasing apoptosis, and modifying GDF9:BMP15 expression

The number of eggs ovulated varies within and between species and is influenced by many variables. However, the regulatory mechanisms remain poorly understood. We previously demonstrated a key role for the oocyte because mice generating oocytes deficient in core 1-derived O-glycans ovulate ∼40-50% more eggs than Controls. Here we analyze the basis of this phenotype using Mutant [core 1 β1,3-galactosyltransferase 1 (C1galt1)(FF):zona pellucida glycoprotein 3 Cre (ZP3Cre)] and Control (C1galt1(FF)) female mice. In culture, Mutant follicles exhibited delayed antrum formation [indicative of follicle stimulant hormone (FSH) dependence] and increased sensitivity to FSH. Although the Mutant estrous cycle was extended, comprehensive endocrine changes were not observed; rather FSH, LH, inhibin B, and anti-Mullerian hormone were temporally altered, revealing estrous cycle stage-specific modifications to the hypothalamic-pituitary-gonadal axis. At proestrus, when FSH levels were decreased in Mutants, ovaries contained more, smaller, preantral follicles. Mutant follicles exhibited reduced levels of apoptosis, and both B-cell lymphoma 2 (Bcl-2) and BCL-2-associated X protein (Bax) were altered compared with Controls. Mutant ovaries also had an increase in the expression ratio of growth differentiation factor 9 (GDF9):bone morphogenetic protein 15 (BMP15) at diestrus. On the basis of these data, we propose that modified oocyte glycoproteins alter GDF9:BMP15 expression modifying follicle development resulting in the generation of more follicles. Thus, the oocyte is a key regulator of follicle development and has a crucial role in determining ovulation rate.

Effects of gonadotropin on Fas and/or FasL expression and proliferation in rat ovary

Although gonadotropin is a dominant hormone involved in promoting ovarian follicle development in females, the mechanism by which gonadotropin regulates follicular development is still unknown. To systematically evaluate the effectiveness of the gonadotropin on apoptosis and proliferation of ovarian cells in vivo, rats were injected subcutaneously with eCG and/or anti-eCG antiserum. Equine chorionic gonadotropin treatment increased ovarian cell proliferation and expression of FSH receptors (FSHR) as revealed by increased immunostaining of proliferating cell nuclear antigen and FSHR in rat ovary. These effects did not occur in a follicular stage-dependent manner. Moreover, these actions were abolished by anti-eCG antiserum. However, granulosa cells exhibited more intense Fas- and FasL-positive immunostaining during all follicular stages in the anti-eCG antiserum group. We used Western blot analysis to confirm these results; Fas and FasL protein contents in rat ovaries were decreased by eCG. Meanwhile, proliferating cell nuclear antigen and FSHR expression were upregulated by eCG. However, all these eCG-induced regulations were reversed by anti-eCG antiserum treatment. Furthermore, there were no significant differences between the anti-eCG antiserum and control groups. These results indicate that eCG promotes follicular development via downregulation of death-inducer Fas/FasL expression and promotion of ovarian cell proliferation, which is partially mediated by FSHR.

The dynamics of the primordial follicle reserve

The female germline comprises a reserve population of primordial (non-growing) follicles containing diplotene oocytes arrested in the first meiotic prophase. By convention, the reserve is established when all individual oocytes are enclosed by granulosa cells. This commonly occurs prior to or around birth, according to species. Histologically, the ‘reserve’ is the number of primordial follicles in the ovary at any given age and is ultimately depleted by degeneration and progression through folliculogenesis until exhausted. How and when the reserve reaches its peak number of follicles is determined by ovarian morphogenesis and germ cell dynamics involving i) oogonial proliferation and entry into meiosis producing an oversupply of oocytes and ii) large-scale germ cell death resulting in markedly reduced numbers surviving as the primordial follicle reserve. Our understanding of the processes maintaining the reserve comes primarily from genetically engineered mouse models, experimental activation or destruction of oocytes, and quantitative histological analysis. As the source of ovulated oocytes in postnatal life, the primordial follicle reserve requires regulation of i) its survival or maintenance, ii) suppression of development (dormancy), and iii) activation for growth and entry into folliculogenesis. The mechanisms influencing these alternate and complex inter-related phenomena remain to be fully elucidated. Drawing upon direct and indirect evidence, we discuss the controversial concept of postnatal oogenesis. This posits a rare population of oogonial stem cells that contribute new oocytes to partially compensate for the age-related decline in the primordial follicle reserve.

Aromatase-null mice expressing enhanced green fluorescent protein in germ cells provide a model system to assess estrogen-dependent ovulatory responses

Enhanced green fluorescent protein (EGFP) has provided us with valuable approaches for tracking living cells. We established a novel line of transgenic mice, which express EGFP in the testis and ovary. Histological analysis demonstrated that spermatids in the testis and oocytes in ovarian follicles beyond preantral stages were positive for EGFP. By exploiting these features, we evaluated ovulatory responses of aromatase-gene (Cyp19a) knockout mouse expressing the EGFP transgene, which is totally anovulatory due to 17β-estradiol (E2) deficiency. Ovulation in the knockout mice was induced by sequential injections of E2 on days 1, 4 and 5, pregnant mare serum gonadotropin on day 4 and human chorionic gonadotropin on day 6. Fluorescent oocytes were readily detectable at 15 h after the last gonadotropin injection in the oviduct under a fluorescence stereomicroscope, even when only one oocyte was present. However, when E2 supplementation on day 4 or day 5 in the regimen was omitted, no ovulated oocytes were detected, indicating that exogenous E2 supplementation at the time of gonadotropin stimulation is necessary to induce ovulation in aromatase-gene knockout mice. Our results further demonstrated that the current mouse line can provide an alternative tool to study germ cell biology, including oogenesis, ovulation and senescence.

In vitro culture of early secondary preantral follicles in hanging drop of ovarian cell-conditioned medium to obtain MII oocytes from outbred deer mice

The ovarian follicle (each contains a single oocyte) is the fundamental functional tissue unit of mammalian ovaries. In humans, it has been long held true that females are born with a maximum number of follicles (or oocytes) that are not only nonrenewable, but also undergoing degeneration with time with a sharply decreased oocyte quality after the age of ∼35. Therefore, it is of importance to isolate and bank ovarian follicles for in vitro culture to obtain fertilizable oocytes later, to preserve the fertility of professional women who may want to delay childbearing, young and unmarried women who may lose gonadal function because of exposure to environmental/occupational hazards or aggressive medical treatments, such as radiation and chemotherapy, and even endangered species and breeds. Although they contributed significantly to the understanding of follicle science and biology, most studies reported to date on this topic were done using the man-made, unnatural inbred animal species. It was found in this study that the conventional two-dimensional microliter drop and three-dimensional hanging drop (HD) methods, reported to be effective for in vitro culture of preantral follicles from inbred mice, are not directly transferrable to outbred deer mice. Therefore, a modified HD method was developed in this study to achieve a much higher (>5 times compared to the best conventional methods) percentage of developing early secondary preantral follicles from the outbred mice to the antral stage, for which, the use of an ovarian cell-conditioned medium and multiple follicles per HD were identified to be crucial. It was further found that the method for in vitro maturation of oocytes in antral follicles obtained by in vitro culture of preantral follicles could be very different from that for oocytes in antral follicles obtained by hormone stimulation in vivo. Therefore, this study should provide important guidance for establishing effective protocols of in vitro follicle culture to preserve the fertility of wildlife and humans outbred by nature.

Emerging roles for LXRs and LRH-1 in female reproduction

Nutritional status is known to control female reproductive physiology. Many reproductive pathologies such as anorexia nervosa, dystocia and preeclampsia, have been linked to body mass index and to metabolic syndrome. Lipid metabolism has also been associated with ovarian, uterine and placental functions. Among the regulators of lipid homeostasis, the Liver X Receptors (LXRs) and the Liver Receptor Homolog-1 (LRH-1), two members of the nuclear receptor superfamily, play a central role. LXRs are sensitive to intracellular cholesterol concentration and decrease plasma cholesterol, allowing to considering them as "cholesterol sensors". LRH-1 shares many target-genes with LXRs and has been considered for a long time as a real orphan nuclear receptor, but recent findings showed that phospholipids are ligands for this nuclear receptor. Acting in concert, LXRs and LRH-1 could thus be sensitive to slight modifications in cellular lipid balance, tightly maintaining their cellular concentrations. These last years, the use of transgenic mice clarified the roles of these nuclear receptors in many physiological functions. This review will be focused on the roles of LXRs and LRH-1 on female reproduction. Their contribution to ovarian endocrine and exocrine functions, as well as uterine and placental physiology will be discussed. The future challenge will thus be to target these nuclear receptors to prevent lipid-associated reproductive diseases in women.

A novel loss-of-function mutation in Npr2 clarifies primary role in female reproduction and reveals a potential therapy for acromesomelic dysplasia, Maroteaux type

We discovered a new spontaneous mutant allele of Npr2 named peewee (pwe) that exhibits severe disproportionate dwarfism and female infertility. The pwe phenotype is caused by a four base-pair deletion in exon 3 that generates a premature stop codon at codon 313 (L313X). The Npr2(pwe/pwe) mouse is a model for the human skeletal dysplasia acromesomelic dysplasia, Maroteaux type (AMDM). We conducted a thorough analysis of the female reproductive tract and report that the primary cause of Npr2(pwe/pwe) female infertility is premature oocyte meiotic resumption, while the pituitary and uterus appear to be normal. Npr2 is expressed in chondrocytes and osteoblasts. We determined that the loss of Npr2 causes a reduction in the hypertrophic and proliferative zones of the growth plate, but mineralization of skeletal elements is normal. Mutant tibiae have increased levels of the activated form of ERK1/2, consistent with the idea that natriuretic peptide receptor type 2 (NPR2) signaling inhibits the activation of the MEK/ERK mitogen activated protein kinase pathway. Treatment of fetal tibiae explants with mitogen activated protein kinase 1 and 2 inhibitors U0126 and PD325901 rescues the Npr2(pwe/pwe) growth defect, providing a promising foundation for skeletal dysplasia therapeutics.

Suppressor of cytokine signaling 4 (SOCS4): moderator of ovarian primordial follicle activation

Mammalian ovarian primordial follicle activation and regulation is considered as one of the most important stages of folliculogenesis and as such requires exquisite control. Selection of quiescent follicles to enter the growing pool determines the rate of supply of maturing follicles over the female reproductive lifespan. To coordinate this process a range of positive and negative input signals contribute to determine follicle fate. This study demonstrates that the cytokine Leukemia Inhibitory Factor (LIF) activates the Janus Kinase 1/Signal Transducers and Activators of Transcription 3 (JAK1/STAT3) signaling pathway in pre-granulosa cells and positively regulates primordial follicle activation. Negative regulation of the JAK/STAT pathway is controlled by the suppressor of cytokine signaling 4 (SOCS4) protein, which target members of negative feedback loops, Cardiotrophin like Cytokine (CLC), Poly (rC) Binding Protein 1 (PCBP1), and Cytosolic Malate Dehydrogenase (MDH1) to suppress follicle growth and development.

Effect of physiological levels of phytoestrogens on mouse oocyte maturation in vitro

Phytoestrogens are a group of naturally occurring compounds that have weak estrogenic activity. Genistein and daidzein are major phytoestrogens produced by soybeans. It has been reported previously that at high concentration, some phytoestrogens inhibit cell cycle progression of mouse germinal vesicle (GV) oocytes, but the environmentally relevant level is much lower. Here we show the effects of low concentrations of the isoflavones genistein, daidzein and the daidzein metabolite, equol, on mouse oocyte maturation. GV oocytes denuded of cumulus cells were cultured in TaM medium containing low levels (5 μM) of genistein, daidzein. or equol. In all cases, the oocytes underwent normal GV break down, first polar body extrusion and became arrested at metaphase II (mII). As judged by fluorescence microscopy, the treated mII oocytes exhibited normal distributions of actin microfilaments, cortical granules and metaphase spindle formation with condensed metaphase chromatin. Moreover, mRNA expression levels of the cytostatic factors Emi2 and Mos were similar to those of their respective controls. These data suggest that exposure of maturing GV oocytes to environmental levels of genistein, daidzein or equol in vitro do not cause negative effects on maturation to produce mII oocytes.

Transplantation of young ovaries restored cardioprotective influence in postreproductive-aged mice

The female cardioprotective advantage, present in mammals of a reproductively competent age, is lost during the transition to a postreproductive state. The role of reproductive hormones in this transition is most evident in women with premature ovarian failure, where reduced estrogen production has been associated with an increased incidence of early death from cardiovascular disease. Previously, we reported that postreproductive-aged mice that received young ovaries displayed an increased life span. Subsequent histopathological analysis suggested the presence of a cardioprotective effect associated with the restoration of ovarian influence. This restoration in postreproductive-aged mice produced a sharp decrease in evidence of significant cardiomyopathy at death, compared with sham-transplanted mice (36.0% vs. 73.3%, respectively). Within the intact transplant group, evidence of cardiomyopathy at death was decreased in mice that were reproductively cycling at the time of transplant, compared with acyclic mice (26.7% vs. 50.0%, respectively). This observation reflects the importance of timing in restoration of ovarian influence in this study. Transplantation of young ovaries to intact, postreproductive-aged female mice provided significant, long-term restoration of a cardioprotective benefit, similar to that previously present during a reproductively competent age. In these mice, restoration of ovarian influence through ovarian transplantation may, in effect, have postponed the advance of age-associated cardiomyopathy to a point where the disease did not reach a clinically relevant threshold during the lifetime of the recipients. These results offer support for previous clinical observations suggesting that hormone replacement therapy can produce divergent results if initiated during the perimenopausal period, compared with the postmenopausal ages.

Notch signaling is involved in ovarian follicle development by regulating granulosa cell proliferation

Notch signaling is an evolutionarily conserved pathway, which regulates cell proliferation, differentiation, and apoptosis. It has been reported that the members of Notch signaling are expressed in mammalian ovaries, but the exact functions of this pathway in follicle development is still unclear. In this study, primary follicles were cultured in vitro and treated with Notch signaling inhibitors, L-658,458 and N-[N-(3,5-Difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT). We found that the cultured follicles completely stopped developing after L-658,458 and DAPT treatment, most of the granulosa cells were detached, and the oocytes were also degenerated with condensed cytoplasma. Further studies demonstrated that the proliferation of granulosa cells was dependent on the Notch signaling. L-658,458 and DAPT treatment inhibited proliferation of in vitro cultured primary granulosa cells and decreased the expression of c-Myc. Lentivirus mediated overexpression of Notch intracellular domain 2, and c-Myc could promote the proliferation of granulosa cells and rescue the growth inhibition induced by L-658,458 and DAPT. In conclusion, Notch signaling is involved in follicular development by regulating granulosa cell proliferation.

Gene expression profiling reveals Cyp26b1 to be an activin regulated gene involved in ovarian granulosa cell proliferation

Activin, a member of the TGF-β superfamily, is an important modulator of FSH synthesis and secretion and is involved in reproductive dysfunctions and cancers. It also regulates ovarian follicle development. To understand the mechanisms and pathways by which activin regulates follicle function, we performed a microarray study and identified 240 activin regulated genes in mouse granulosa cells. The gene most strongly inhibited by activin was Cyp26b1, which encodes a P450 cytochrome enzyme that degrades retinoic acid (RA). Cyp26b1 has been shown to play an important role in male germ cell meiosis, but its expression is largely lost in the ovary around embryonic d 12.5. This study demonstrated that Cyp26b1 mRNA was expressed in granulosa cells of follicles at all postnatal developmental stages. A striking inverse spatial and temporal correlation between Cyp26b1 and activin-βA mRNA expression was observed. Cyp26b1 expression was also elevated in a transgenic mouse model that has decreased activin expression. The Cyp26 inhibitor R115866 stimulated the proliferation of primary cultured mouse granulosa cells, and a similar effect was observed with RA and activin. A pan-RA receptor inhibitor, AGN194310, abolished the stimulatory effect of either RA or activin on granulosa cell proliferation, indicating an involvement of RA receptor-mediated signaling. Overall, this study provides new insights into the mechanisms of activin action in the ovary. We conclude that Cyp26b1 is expressed in the postnatal mouse ovary, regulated by activin, and involved in the control of granulosa cell proliferation.

Theca: the forgotten cell of the ovarian follicle

Theca cells function in a diverse range of necessary roles during folliculogenesis; to synthesize androgens, provide crosstalk with granulosa cells and oocytes during development, and provide structural support of the growing follicle as it progresses through the developmental stages to produce a mature and fertilizable oocyte. Thecal cells are thought to be recruited from surrounding stromal tissue by factors secreted from an activated primary follicle. The precise origin and identity of these recruiting factors are currently not clear, but it appears that thecal recruitment and/or differentiation involves not just one signal, but a complex and tightly controlled combination of multiple factors. It is clear that thecal cells are fundamental for follicular growth, providing all the androgens required by the developing follicle(s) for conversion into estrogens by the granulosa cells. Their function is enabled through the establishment of a vascular system providing communication with the pituitary axis throughout the reproductive cycle, and delivering essential nutrients to these highly active cells. During development, the majority of follicles undergo atresia, and the theca cells are often the final follicular cell type to die. For those follicles that do ovulate, the theca cells then undergo hormone-dependent differentiation into luteinized thecal cells of the corpus luteum. While the theca is an essential component of follicle development and ovulation, we do not yet fully understand the control of recruitment and function of theca cells, an important consideration since their function appears to be altered in certain causes of infertility.

Ovarian status influenced the rate of body-weight change but not the total amount of body-weight gained or lost in female CBA/J mice

Previously we reported that prepubertally ovariectomized mice that received young, transplanted ovaries at a postreproductive age displayed a 40% increase in life expectancy. To study this increase in life expectancy in greater detail, prepubertally ovariectomized and ovary-intact CBA/J mice underwent ovarian transplantation at 11 months with 60-day-old ovaries or a sham surgery. Life span was significantly increased in transplant recipients. Body-weight changes of mice in each group were measured from the time of surgery (11 months) to death. Neither ovariectomy nor ovarian transplantation influenced the amount of peak body-weight attained or body-weight retained at death. However, the time (days) to peak body-weight was decreased by ovariectomy and ovarian transplant recipients displayed a trend toward an increase in time to peak weight. In addition, ovarian transplantation decreased the rate of weight loss to death. These results demonstrate that ovarian status, examined by means of ovariectomy and ovarian transplantation, clearly influenced the rate of weight change, but not the total amount of weight gain or loss in female mice.

Ovarian aging: mechanisms and clinical consequences

Menopause is the final step in the process referred to as ovarian ageing. The age related decrease in follicle numbers dictates the onset of cycle irregularity and the final cessation of menses. The parallel decay in oocyte quality contributes to the gradual decline in fertility and the final occurrence of natural sterility. Endocrine changes mainly relate to the decline in the negative feedback from ovarian factors at the hypothalamo-pituitary unit. The declining cohort of antral follicles with age first results in gradually elevated FSH levels, followed by subsequent stages of overt cycle irregularity. The gradual decline in the size of the antral follicle cohort is best represented by decreasing levels of anti-Mullerian hormone. The variability of ovarian ageing among women is evident from the large variation in age at menopause. The identification of women who have severely decreased ovarian reserve for their age is clinically relevant. Ovarian reserve tests have appeared to be fairly accurate in predicting response to ovarian stimulation in the assisted reproductive technology (ART) setting. The capacity to predict the chances for spontaneous pregnancy or pregnancy after ART appears very limited. As menopause and the preceding decline in oocyte quality seem to have a fixed time interval, tests that predict the age at menopause may be useful to assess individual reproductive lifespan. Especially genetic studies, both addressing candidate gene and genome wide association, have identified several interesting loci of small genetic variation that may determine fetal follicle pool development and subsequent wastage of his pool over time. Improved knowledge of the ovarian ageing mechanisms may ultimately provide tools for prediction of menopause and manipulation of the early steps of folliculogenesis for the purpose of contraception and fertility lifespan extension.

Roles for transforming growth factor beta superfamily proteins in early folliculogenesis

Primordial follicle formation and the subsequent transition of follicles to the primary and secondary stages encompass the early events during folliculogenesis in mammals. These processes establish the ovarian follicle pool and prime follicles for entry into subsequent growth phases during the reproductive cycle. Perturbations during follicle formation can affect the size of the primordial follicle pool significantly, and alterations in follicle transition can cause follicles to arrest at immature stages or result in premature depletion of the follicle reserve. Determining the molecular events that regulate primordial follicle formation and early follicle growth may lead to the development of new fertility treatments. Over the last decade, many of the growth factors and signaling proteins that mediate the early stages of folliculogenesis have been identified using mouse genetic models, in vivo injection studies, and ex vivo organ culture approaches. These studies reveal important roles for the transforming growth factor beta (TGF-beta) superfamily of proteins in the ovary. This article reviews these roles for TGF-beta family proteins and focuses in particular on work from our laboratories on the functions of activin in early folliculogenesis.

HOX cofactors expression and regulation in the human ovary

BACKGROUND

HOX cofactors enhance HOX binding affinities and specificities and increase HOX's unique functional activities. The expression and the regulation of HOX cofactors in human ovaries are unknown.

METHODS

In this study, the expression of HOX cofactors, PBX1, PBX2, and MEIS1/2, were examined by using RT-PCR, immunofluorescence in cultured immortalized human granulosa (SVOG) cells. The distribution of these HOX cofactors in human ovaries was examined by immunohistochemistry. The effects of growth differentiation factor-9 (GDF-9) and follicle-stimulating hormone (FSH) on PBX2 in SVOG cells were investigated by western blot analysis. Binding activities of HOXA7 and PBX2 to the specific sequences in granulosa cells were determined by electrophoretic mobility shift assay (EMSA).

RESULTS AND CONCLUSION

In SVOG cells, PBX1, PBX2 and MEIS1/2 were expressed during cell culture. In normal human ovaries, PBX1 and MEIS1/2 were expressed in granulosa cells at essentially all stages of follicular development. These cofactors were expressed in the nuclei of the granulosa cells from the primordial to the secondary follicles, whereas beyond multilayered follicles was observed in the cytoplasm. The co-expression of PBX1 and MEIS1/2 in granulosa cells in normal human ovaries suggested that MEIS1/2 might control PBX1 sublocalization, as seen in other systems. PBX2 was not expressed or weakly expressed in the primordial follicles. From the primary follicles to the preovulatory follicles, PBX2 expression was inconsistent and the expression was found in the granulosa cell nuclei. The PBX2 expression pattern is similar to HOXA7 expression in ovarian follicular development. Furthermore, FSH down-regulated, GDF-9 did not change PBX2 expression, but co-treatment of the granulosa cells with FSH and GDF-9 up-regulated PBX2 expression. These results implicated a role for PBX2 expression in the steroidogenic activities of granulosa cells in humans. Moreover, PBX2 and HOXA7 bound together to the Pbx sequence, but not to the EMX2 promoter sequence, in SVOG cells. Our findings indicate that HOX cofactors expression in normal human ovary is temporally and spatially specific and regulated by FSH and GDF-9 in granulosa cells. HOX proteins may use different HOX cofactors, depending on DNA sequences that are specific to the granulosa cells.

Potential regulatory functions of microRNAs in the ovary

The interactions between ovarian germ and somatic cells and expression of several intraovarian autocrine/paracrine regulators are major contributing factors in the ovary. These intraovarian mediators regulate various ovarian cellular activities including cell growth, differentiation, and apoptosis, which are critical in follicular development. MicroRNAs (miRNAs) have emerged as key components of posttranscriptional gene expression. Recent evidence generated in mice implicates the regulatory function of miRNAs in oocyte maturation and ovarian follicular development. In the human, miRNAs may target specific gene expression in granulosa cells and participate in establishment and progression of ovarian cancer. Here, we review the currently available information on the expression and potential regulatory functions of miRNAs in the ovary under normal and pathologic conditions. Understanding the underlying mechanisms of how ovarian germ cell and somatic cell miRNAs are regulated and identifying their specific target genes and their functions may lead to the development of strategies to achieve target-specific gene regulation for the prevention and treatment of various ovarian disorders.

Effects of a low oral dose of diethylstilbestrol (DES) on reproductive tract development in F1 female CD-1 mice

The synthetic estrogen diethylstilbestrol (DES) is a model to study the effects on female reproductive tract of endocrine disrupting chemicals interacting with estrogen receptors. Pregnant CD-1 mice were given daily by gavage 10microg/kg bw of DES (the lower range of therapeutic exposure) during gestational days 9-16, critical period for reproductive tract development. Parameters of sexual development were recorded after weaning and at sexual maturation. No signs of general toxicity were observed in dams. In DES-treated group, reduced litter weight during lactation and earlier vaginal patency was observed. Uterus weight was increased in F1 treated females at weaning. Histological analysis showed reduced endometrium thickness and increased polyovular follicles, irregular and oocytes with condensed chromatin in the ovary at sexual maturity. Prenatal DES oral administration induces subtle but significant effects on puberty onset, uterine and ovary morphology.

The proregion of mouse BMP15 regulates the cooperative interactions of BMP15 and GDF9

Bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9) are secreted by the mammalian oocyte and are essential for ovarian follicular development, ovulation, and fertility. However, the secreted forms of the BMP15 and GDF9 proteins and the nature of cooperative molecular interactions between BMP15 and GDF9 previously reported have not been fully characterized. In this study, we found that recombinant mouse BMP15 and GDF9 are secreted as cleaved mature and proregion proteins, with BMP15 also secreted as uncleaved promature protein. Noncovalent interactions were identified between the mature and proregion proteins of each growth factor. Moreover, GDF9 mature protein was found to coimmunoprecipitate with the BMP15 proregion, suggestive of a heteromeric association between BMP15 and GDF9. Mouse GDF9 was found to exist mostly as a dimer of mature protein, in both the presence and absence of BMP15. In contrast, BMP15 formed mostly multimers of proregion and mature protein when combined with GDF9, providing further evidence for heteromeric interaction. Mouse BMP15 was found to act cooperatively with GDF9 in a rat granulosa cell thymidine incorporation bioassay and to signal through the BMPR2 and ACVR1B/TGFBR1/ACVR1C receptor-mediated pathways. Immunoneutralization experiments using GDF9 mature protein antibody indicated that these cooperative interactions are species specific. Additionally, immunoneutralization with proregion antibodies highlighted the involvement of the BMP15 proregion in BMP15/GDF9 cooperative interactions. Taken together, these findings support a novel hypothesis where the extracellular cooperative interactions of recombinant mouse BMP15 and GDF9 are multimeric, involving the proregion of BMP15, and may well be species specific.

Potential applications of equine genomics in dissecting diseases and fertility

Following the recent development of high-resolution gene maps and generation of several basic tools and resources to use them in analyzing traits that are economically important to horse owners, genome analysis in horses is witnessing a shift towards developing an ability to analyze complex traits. The likelihood of this happening in the very near future is great, mainly because of the recent availability of the whole genome sequence in the horse. The latter has triggered the development of novel tools like SNP-chip and expression arrays that will permit rapid genome-wide analysis. While these tools will be used for a range of multi-factorial disease traits, attempts are underway to develop focused tools that can target reproduction, fertility and sex determination. For this, a catalog of sex and reproduction related (SRR) genes is being developed in horses. A recently developed dense map of the horse Y chromosome will provide genes that are expressed exclusively in males and, therefore, have an impact on stallion fertility. Overall, these advances in equine genome analysis hold promise for improved diagnosis and treatment of various conditions in horses.

Mouse fertility is enhanced by oocyte-specific loss of core 1-derived O-glycans

Regulation of the number of eggs ovulated by different mammalian species remains poorly understood. Here we show that oocyte-specific deletion at the primary follicle stage of core 1 beta1,3-galactosyltransferase (T-synthase; generates core 1-derived O-glycans), leads to a sustained increase in fertility. T-syn mutant females ovulated 30-50% more eggs and had a sustained increase in litter size compared to controls. Ovarian weights and follicle numbers were greater in mutants, but follicular apoptosis was not decreased. The number of follicles entering the growing pool was unaltered, but 3-wk mutants ovulated fewer eggs, suggesting that increased fertility results from prolonged follicle development. T-syn mutant ovaries also contained numerous multiple-oocyte follicles (MOFs) that appeared to form by adjacent, predominantly preantral, follicles joining--a new mechanism for MOF generation. Ovulation of multiple eggs from MOFs was not the reason for increased fertility based on ovulated egg and corpora lutea numbers. Thus, the absence of T-synthase caused modified follicular development, leading to the maturation and ovulation of more follicles, to MOF formation at late stages of folliculogenesis, and to increased fertility. These results identify novel roles for glycoproteins from the oocyte as suppressors of fertility and regulators of follicular integrity in the mouse.

Opportunities and challenges in applying genomics to the study of oogenesis and folliculogenesis in farm animals

Ovarian oogenesis and folliculogenesis are complex and coordinated biological processes which require a series of events that induce morphological and functional changes within the follicle, leading to cell differentiation and oocyte development. In this context, the challenge of the researchers is to describe the dynamics of gene expression in the different compartments and their interactions during the follicular programme. In recent years, high-throughput arrays have become a powerful tool with which to compare the whole population of transcripts in a single experiment. Here, we review the challenges of applying genomics to this model in farm animal species. The first limitation lies in limited the availability of biological material, which makes the study of the follicle compartments (oocyte, granulosa cells and thecal cells) or early embryo much more difficult. The concept of observing all transcripts at once is very attractive but despite progress in sequencing, the genome annotation remains very incomplete in non-model species. Particularly, oogenesis and early embryo development relate to the high proportion of unknown expressed sequence tags. Then, it is important to consider post-transcriptional and translational regulation to understand the role of these genes. Ultimately, these new inferred insights will still have to be validated by functional approaches. In addition toin vitroorex vivofunctional approaches, both ‘natural mutant’ ewe models and RNA interference represent, at the moment, the best hope for functional genomics. Advances in our understanding of reproductive physiology should be facilitated by gene expression data exchange and translation into a better understanding of the underlying biological phenomena.

Recent advances in the study of genes involved in non-syndromic premature ovarian failure

Premature ovarian failure (POF) is a common pathology leading to infertility affecting about 1% of women under 40 years old. In POF patients, the ovarian dysfunction is characterized by the lack of the ovarian response to close a negative feedback loop on the synthesis of pituitary gonadotropins. Although the majority of cases are considered as idiopathic, diverse aetiologies have been associated, including genetic factors. Up to now, the potential genetic causes of non-syndromic POF have been established mainly by genetic linkage analysis of familial cases or by the screening of mutations in candidate genes based on animal models. Here, we review recent advances in the study of candidate genes.

Oocyte quality and maternal control of development

The oocyte is a unique and highly specialized cell responsible for creating, activating, and controlling the embryonic genome, as well as supporting basic processes such as cellular homeostasis, metabolism, and cell cycle progression in the early embryo. During oogenesis, the oocyte accumulates a myriad of factors to execute these processes. Oogenesis is critically dependent upon correct oocyte-follicle cell interactions. Disruptions in oogenesis through environmental factors and changes in maternal health and physiology can compromise oocyte quality, leading to arrested development, reduced fertility, and epigenetic defects that affect long-term health of the offspring. Our expanding understanding of the molecular determinants of oocyte quality and how these determinants can be disrupted has revealed exciting new insights into the role of oocyte functions in development and evolution.

Are steroids dispensable for meiotic resumption in mammals?

Meiosis of vertebrate oocytes is a protracted process initiated within differentiated oocytes before the first meiotic arrest of the first meiotic division. Meiosis normally resumes in response to the stimulation of ovulation, proceeding to metaphase of the second meiotic division. In fish and amphibian oocytes, this resumption is triggered by follicular steroids. By contrast, the role of steroids in the resumption of mammalian oocyte maturation is less clear. Specifically, mammalian meiotic maturation proceeds undisturbed even when steroid production is severely suppressed. This puzzling mammalian divergence has been reexamined recently. Here, we review the published data and conclude that steroids are not necessary for the resumption of mammalian meiosis. Nevertheless, steroids are probably involved in follicular growth, somatic-cell differentiation and the acquisition of developmental competence of mature ova.