Morphometric study of the human neonatal ovary

Current Insights in Prolactin Signaling and Ovulatory Function

Prolactin (PRL) is a pleiotropic hormone released from lactotrophic cells of the anterior pituitary gland that also originates from extrapituitary sources and plays an important role in regulating lactation in mammals, as well as other actions. Acting in an endocrine and paracrine/autocrine manner, PRL regulates the hypothalamic-pituitary-ovarian axis, thus influencing the maturation of ovarian follicles and ovulation. This review provides a detailed discussion of the current knowledge on the role of PRL in the context of ovulation and ovulatory disorders, particularly with regard to hyperprolactinemia, which is one of the most common causes of infertility in women. Much attention has been given to the PRL structure and the PRL receptor (PRLR), as well as the diverse functions of PRLR signaling under normal and pathological conditions. The hormonal regulation of the menstrual cycle in connection with folliculogenesis and ovulation, as well as the current classifications of ovulation disorders, are also described. Finally, the state of knowledge regarding the importance of TIDA (tuberoinfundibular dopamine), KNDγ (kisspeptin/neurokinin B/dynorphin), and GnRH (gonadotropin-releasing hormone) neurons in PRL- and kisspeptin (KP)-dependent regulation of the hypothalamic-pituitary-gonadal (HPG) axis in women is reviewed. Based on this review, a rationale for influencing PRL signaling pathways in therapeutic activities accompanying ovulation disorders is presented.

Predicting Infertility: How Genetic Variants in Oocyte Spindle Genes Affect Egg Quality

Successful reproduction relies on the union of a single chromosomally normal egg and sperm. Chromosomally normal eggs develop from precursor cells, called oocytes, that have undergone accurate chromosome segregation. The process of chromosome segregation is governed by the oocyte spindle, a unique cytoskeletal machine that splits chromatin content of the meiotically dividing oocyte. The oocyte spindle develops and functions in an idiosyncratic process, which is vulnerable to genetic variation in spindle-associated proteins. Human genetic variants in several spindle-associated proteins are associated with poor clinical fertility outcomes, suggesting that heritable etiologies for oocyte dysfunction leading to infertility exist and that the spindle is a crux for female fertility. This chapter examines the mammalian oocyte spindle through the lens of human genetic variation, covering the genes TUBB8, TACC3, CEP120, AURKA, AURKC, AURKB, BUB1B, and CDC20. Specifically, it explores how patient-identified variants perturb spindle development and function, and it links these molecular changes in the oocyte to their cognate clinical consequences, such as oocyte maturation arrest, elevated egg aneuploidy, primary ovarian insufficiency, and recurrent pregnancy loss. This discussion demonstrates that small genetic errors in oocyte meiosis can result in remarkably far-ranging embryonic consequences, and thus reveals the importance of the oocyte's fine machinery in sustaining life.

Three major reasons why transgenerational effects of radiation are difficult to detect in humans

PURPOSE

Ionizing radiation can induce mutations in germ cells in various organisms, including fruit flies and mice. However, currently, there is no clear evidence for the transgenerational effects of radiation in humans. This review is an effort to identify possible reasons for the lack of such observations.

METHODS

Literature search and narrative review.

RESULTS

1) In both mice and humans, resting oocytes locate primarily in the cortical region of the ovary where the number of blood vessels is very low especially when young and extra-cellular material is rich, and this region is consequently hypoxic, which probably leads to immature oocytes being resistant to the cell killing and mutagenic effects of radiation. 2) In studies of spermatogonia, the mouse genes used for specific locus test (SLT) studies, which include coat color genes, were hypermutable when compared to many other genes. Recent studies which examined over 1000 segments of genomic DNA indicate that the induction rate of deletion mutation per segment was on the order of 10^-6 per Gy, which is one order of magnitude lower than that obtained from the SLT data. Therefore, it appears possible that detecting any transgenerational effects of radiation following human male exposures will be difficult due to a lack of mutable marker genes. 3) Fetal malformations were examined in studies in humans, but the genetic component in such malformations is low, and abnormal fetuses are prone to undergo miscarriage which does not occur in mice, and which leads to difficulties in detecting transgenerational effects.

CONCLUSION

The lack of clear evidence for radiation effects in humans probably does not result from any problem in the methodologies used but may be due largely to biological properties. Currently, whole genome sequencing studies of exposed parents and offspring are planned, but ethical guidelines need to be followed to avoid discrimination, which had once happened to the atomic bomb survivors.

Ovarian Morphometric and Histologic Characteristics and Correlation with Clinical Factors: A Cross-Sectional Study

Reproductive lifespan is determined by the reserve of ovarian follicles; their quality and quality determine the fertility potential at a given point in time for a particular individual. Inter-individual variations related to morphometry, laterality, medical history, demographic characteristics and ethnicity may impact ovarian histology, which however, has not been extensively studied or documented. The present cross-sectional study aims to investigate the potential association of clinical factors (age, medical and obstetric history) with ovarian morphometry and histology in females of reproductive age in the local population. The sample included 31 specimens of whole human ovaries, obtained from surgical/autopsy procedures in reproductive-aged women, processed at the Pathology Department. Morphometric characteristics were assessed, including shape, color, length, width, thickness and gross ovarian pathology. Random samples of specific dimensions were histologically examined to determine follicular counts. The results were analyzed statistically in correlation to morphometric characteristics and medical history. The majority of the patients had oval-shaped ovaries (77.8% right; 92.3% left; p = 0.368) of whitish color (38.9% right; 46.2% left; p > 0.999). Right ovaries had significantly greater length, width and volume (p-values 0.018, 0.040 and 0.050, respectively). Thickness was equivalent, as well as follicular distribution of all classes. Age correlated inversely with ovarian volume and primordial/primary follicular count on histology. Women with a caesarian-section history yielded significantly lower primordial/primary follicular counts. As estimated by ovarian histology, macroscopic and clinical factors may be significantly associated with actual ovarian reserve.

Regulation of Oocyte Apoptosis: A View from Gene Knockout Mice

Apoptosis is a form of programmed cell death that plays a critical role in cellular homeostasis and development, including in the ovarian reserve. In humans, hundreds of thousands of oocytes are produced in the fetal ovary. However, the majority die by apoptosis before birth. After puberty, primordial follicles develop into mature follicles. While only a large dominant follicle is selected to ovulate, smaller ones undergo apoptosis. Despite numerous studies, the mechanism of oocyte death at the molecular level remains elusive. Over the last two and a half decades, many knockout mouse models disrupting key genes in the apoptosis pathway have been generated. In this review, we highlight some of the phenotypes and discuss distinct and overlapping roles of the apoptosis regulators in oocyte death and survival. We also review how the transcription factor p63 and its family members may trigger oocyte apoptosis in response to DNA damage.

Anti-Müllerian hormone independently affect mtDNA copy number in human granulosa cells

BACKGROUND

Recently, as a delayed childbearing trend is emerging in modern women's adulthood, diminished reproductive potential due to age-related changes is more prevalent. Reduction in the abundance of mitochondrial DNA (mtDNA) copies and circulating anti-Müllerian hormone (AMH) have been separately reported with aging, contributing to the decrease in successful reproduction. However, there are limited reports on the impact of age on mtDNA and AMH in the same individual and whether mtDNA copy numbers are influenced by age and AMH.

METHODS

In the present study, we utilized a real-time quantitative PCR (RT-qPCR) to quantify the mtDNA copy number of granulosa cells obtained from 43 women undergoing an in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) program.

RESULTS

According to our analysis, a significant correlation was observed between age and mtDNA copy number (r = -0.54, P < 0.001) and between age and AMH level (r = -0.48, P < 0.001) of the same individual. There was also a positive correlation between mtDNA copy number and AMH (r = 0.88, P < 0.001) with AMH level falling as mtDNA decreases. In our regression, age and AMH were shown to have low collinearity (VIF = 1.297) but only AMH was correlated with mtDNA quantity (P < 0.001).

CONCLUSION

Our study suggests that both mtDNA and AMH abundance are influenced by age and that AMH levels independently affect mtDNA copy number regardless of age. Further research is required to understand the role of AMH on mitochondria bioenergetics.

OUP accepted manuscript

The pathways of gametogenesis encompass elaborate cellular specialization accompanied by precise partitioning of the genome content in order to produce fully matured spermatozoa and oocytes. Transcription factors are an important class of molecules that function in gametogenesis to regulate intrinsic gene expression programs, play essential roles in specifying (or determining) germ cell fate and assist in guiding full maturation of germ cells and maintenance of their populations. Moreover, in order to reinforce or redirect cell fate in vitro, it is transcription factors that are most frequently induced, over-expressed or activated. Many reviews have focused on the molecular development and genetics of gametogenesis, in vivo and in vitro, in model organisms and in humans, including several recent comprehensive reviews: here, we focus specifically on the role of transcription factors. Recent advances in stem cell biology and multi-omic studies have enabled deeper investigation into the unique transcriptional mechanisms of human reproductive development. Moreover, as methods continually improve, in vitro differentiation of germ cells can provide the platform for robust gain- and loss-of-function genetic analyses. These analyses are delineating unique and shared human germ cell transcriptional network components that, together with somatic lineage specifiers and pluripotency transcription factors, function in transitions from pluripotent stem cells to gametes. This grand theme review offers additional insight into human infertility and reproductive disorders that are linked predominantly to defects in the transcription factor networks and thus may potentially contribute to the development of novel treatments for infertility.

A combination containing natural extracts of clove, Sophora flower bud, and yam improves fertility in aged female mice via multiple mechanisms

INTRODUCTION

With society development, the age at which women choose to have children has been gradually delayed. To improve the reduced fertility in women at advanced maternal age, we developed a combination containing natural extracts from clove, Sophora flower bud and Chinese yam with a mass ratio 15:6:10 and named it as DACHAO.

METHODS AND RESULTS

We then gavage DACHAO at a dose of 310 mg/kg BW to female mice at 10 month of age and investigated its effects on ovarian functions. Using MitoTracker probes, ROS, and JC-1 staining, we found that DACHAO treatment improved mitochondria functions in oocytes from aged mice. We also observed increased blastocyst formation when mature oocytes from control and DACHAO treated mice were for IVF and in vitro embryo culture. Cell counting and TUNEL assay further revealed increased cell numbers and decreased apoptosis in blastocysts of DACHAO group. After control or DACHAO treated mice being mated with fertile male mice, fertility test revealed a greater first litter size in the DACHAO group. Further studies demonstrated that DACHAO treatment could alleviate the retarded ovarian function in aged mice via changes in serum hormone levels, over-expression of antioxidant factors, under-expression of inflammation-related factors, and reduced apoptosis in the ovaries.

DISCUSSION

Thus, the new combination DACHAO will be a good choice in clinic to improve ovarian functions for women at advanced maternal age.

Spatial and temporal changes in follicle distribution in the human ovarian cortex

RESEARCH QUESTION

How does follicle distribution evolve in the human ovarian cortex between the ages of 20 and 35 years?

DESIGN

Fragments of ovarian cortex from women undergoing unilateral oophorectomy for fertility preservation were obtained for quantitative histological assessment, including recording the two-dimensional coordinates of the follicles. Data were analysed using spatial statistical methods.

RESULTS

A total of 53 ovarian cortex tissue samples, containing 1-803 follicles each, were obtained from 14 women aged 20-35 years. Primordial and transitory follicles lay in a clustered manner in the human ovarian cortex, with an average cluster radius of around 270 µm (95% confidence interval 154-377 µm; n = 49). Follicle density declined with age (P = 0.006, n = 13), and the distance from the nearest neighbouring follicle increased (P = 0.004, n = 13). Cluster radius decreased with age (P = 0.02, n = 13), but the degree of clustering tended to increase (P = 0.11, n = 13). In the majority of the samples, follicles at different stages lay in different clusters (P < 0.05, n = 13).

CONCLUSIONS

This study shows that primordial and transitory follicles lie in different clusters in the human ovarian cortex. Spatio-temporal computer simulation suggests that interfollicular signals may hinder follicle loss and may therefore drive clustered follicle distribution. In clinical practice, the woman's age should be taken into account when assessing follicle density, as follicle distribution is increasingly clustered with advancing age.

Ovarian cryopreservation for children aged 3 years or younger: A report of three cases

Ovarian tissue cryopreservation has recently been performed as an option for fertility preservation in prepubertal girls with cancer. In this study, ovarian tissue was cryopreserved from 3 girls of 3 years of age or younger during a 3-year period at our institution. Case 1 was a 1-year-old girl, who was diagnosed with a yolk sac tumor in the sacral region. Case 2 was a 2-year-old girl, who was diagnosed with retroperitoneal neuroblastoma. Case 3 was a 3-year-old girl, who was diagnosed with cerebellar medulloblastoma. All patients had planned to undergo chemotherapy that would affect the ovarian reserve. Because these patients were toddlers, consideration of ethics, the surgical procedure and postoperative management, and optimal method for freezing ovarian tissue was necessary, although gynecologists rarely experience these challenges in daily clinical practice. We herein present the clinical course of these three cases and discuss the peculiarities and countermeasures of ovarian cryopreservation in children.

PTEN and FOXO3 expression in the prenatal and postnatal human ovary

PURPOSE

The objective of this study was to analyse the expression and cellular localization of FOXO3, pFOXO3 and PTEN throughout human ovary development both before and after birth.

METHODS

Foetal, pubertal and adult paraffin-embedded ovarian samples were analysed by immunohistochemistry for cellular localization of FOXO3, pFOXO3 and PTEN proteins. Protein and mRNA expression were analysed by western blot and real time PCR, respectively, from fresh biopsies.

RESULTS

PTEN was not detected by immunohistochemistry in germ cells and follicles of foetal, pubertal and adult ovaries. Occasional PTEN immunoreactive granulosa cells were found in atretic antral follicles in the adult ovary. Western blot analysis showed low levels of PTEN protein. Nuclear FOXO3-expressing primordial follicles represented a variable proportion of the ovarian reserve. The presence of FOXO3-expressing primordial follicles was very low in foetal ovary; although always represented in a low proportion, prevalence increased during pubertal and adult life.

CONCLUSION

Our results seem to indicate that two subpopulations of primordial follicles, i.e. nuclear FOXO3-expressing and no FOXO3-expressing primordial follicles are found in the postnatal human ovary. This scenario suggests that FOXO3 could be acting as in the mouse model, preventing primordial follicle activation. However, the strategy would not be an "all or nothing" system as in mouse ovary but rather a selected subpopulation of primordial follicles preserved to ensure long-term fertility.

Establishment and depletion of the ovarian reserve: physiology and impact of environmental chemicals

The reproductive life span in women starts at puberty and ends at menopause, following the exhaustion of the follicle stockpile termed the ovarian reserve. Increasing data from experimental animal models and epidemiological studies indicate that exposure to a number of ubiquitously distributed reproductively toxic environmental chemicals (RTECs) can contribute to earlier menopause and even premature ovarian failure. However, the causative relationship between environmental chemical exposure and earlier menopause in women remains poorly understood. The present work, is an attempt to review the current evidence regarding the effects of RTECs on the main ovarian activities in mammals, focusing on how such compounds can affect the ovarian reserve at any stages of ovarian development. We found that in rodents, strong evidence exists that in utero, neonatal, prepubescent and even adult exposure to RTECs leads to impaired functioning of the ovary and a shortening of the reproductive lifespan. Regarding human, data from cross-sectional surveys suggest that human exposure to certain environmental chemicals can compromise a woman's reproductive health and in some cases, correlate with earlier menopause. In conclusion, evidences exist that exposure to RTECs can compromise a woman's reproductive health. However, human exposures may date back to the developmental stage, while the adverse effects are usually diagnosed decades later, thus making it difficult to determine the association between RTECs exposure and human reproductive health. Therefore, epidemiological surveys and more experimental investigation on humans, or alternatively primates, are needed to determine the direct and indirect effects caused by RTECs exposure on the ovary function, and to characterize their action mechanisms.

The ovarian germinal reserve and apoptosis-related proteins in the infant and adolescent human ovary

Background

Normal pubertal ovary displays all stages of follicular development and a biased BAX/BCL2 protein ratio in favor of pro-apoptotic BAX protein comparable to the adult ovary. However, adolescents suffering malignant extra-gonadal disease show a limited follicle development after cytotoxic drug treatment and a reduced capacity of in vitro follicle growth. We evaluated the expression of pro- and anti-apoptotic members of the BCL2 gene family, the FAS/FAS-L proteins from the extrinsic apoptosis pathway, the germ-cell-specific marker VASA, the pluripotency marker OCT3/4, and markers of early and late apoptosis in the ovary of pubertal patients with malignant extra-gonadal disease, which received or not pre-surgery chemotherapy, entering a cryopreservation program.

Results

Ovarian biopsies from 12 adolescent girls were screened for follicle count and expression of VASA, OCT3/4, BAX, BCL2, MCL1L and S, cleaved-BID, FAS/FAS-L and CASPASE 3 through immunohistochemistry, western blot and RT-PCR. All stages of folliculogenesis, from primordial to antral follicle, were present in all 12 patients analyzed. VASA and most of the screened apoptosis-related genes showed a pattern of immune-expression comparable to that previously reported. OCT3/4 showed a cytoplasmic localization in the great majority of the primordial follicles; however, in some cases the localization was nuclear. In addition, OCT3/4B showed a significant reduction compared to OCT3/4A. Unexpectedly, BCL2 was detected at all stages of folliculogenesis, associated to the Balbiani’s body in the primordial follicles, regardless of whether patients had or had not received chemotherapy, ruling out the possibility that its expression is a protective response to chemotherapy.

Conclusions

These findings reveal new information on the morphological status of the follicular reserve and the expression of apoptosis-related genes in histologically normal adolescent ovary from patients undergoing extragonadal cancer. The unexpected expression of apoptosis-inhibiting BCL2 protein, both in patients that had or had not received chemotherapy, opens a new avenue for thorough investigations. Moreover, the nuclear localization of OCT3/4 protein in primordial follicle-enclosed oocytes suggests a possible increased activity of ovarian stem cells in response to chemotherapy and/or extragonadal cancer. This new information can be essential for a better managing of in vitro culture of follicles that can be removed by filtration from preserved ovarian tissue, especially in girls that entered a cryopreservation program.

Programmed cell death in the human ovary

During a woman's reproductive life, only about 400 primordial follicles will develop into a preovulatory follicle and undergo ovulation, releasing an oocyte available for fertilization. The process of formation and selection of these follicles is complex and involves a multistep process characterized by a balance between survival and death of the oocytes and the surrounding follicular cells. Although the mechanisms underlying such process are not completely clarified yet, it is common idea that they can occur through various types of programmed cellular death (PCD). Since atresia is the principal destiny of the ovarian follicles, it is relevant to understand how this process takes place and how it is regulated. In this review, after a summary description of folliculogenesis in humans, the main mechanisms of atresia reported to occur during folliculogenesis from birth to adult age, in the human ovary and in other mammals when appropriate, are described.

Oocyte Quality Control: Causes, Mechanisms, and Consequences

Oocyte quality and number are key determinants of reproductive life span and success. These variables are shaped in part by the elimination of oocytes that experience problems during the early stages of meiosis. Meiotic prophase-I marks an extended period of genome vulnerability in which epigenetic reprogramming unleashes retroelements and hundreds of DNA double-strand breaks (DSBs) are inflicted to initiate the programmed recombination required for accurate chromosome segregation at the first meiotic division. Expression of LINE-1 retroelements perturbs several aspects of meiotic prophase and is associated with oocyte death during the early stages of meiotic prophase I. Defects in chromosome synapsis and recombination also trigger oocyte loss, but typically at a later stage, as cells transition into quiescence and form primordial follicles. Interrelated pathways that signal defects in DSB repair and chromosome synapsis mediate this late oocyte attrition. Here, I review our current understanding of early and late oocyte attrition based on studies in mouse and describe how these processes appear to be both distinct and overlapping and how they help balance the quality and size of oocyte reserves to maximize fecundity.

Female fertility preservation in the pediatric and adolescent cancer patient population

The 5-year survival rate for childhood cancer is over 80%, thereby increasing the number of young women facing infertility in the future because of the gonadotoxic effects of chemotherapy and radiation. The gonadotoxic effects of childhood cancer treatment vary by the radiation regimen and the chemotherapeutic drugs utilized. Although the American Society of Clinical Oncology guidelines recommend fertility preservation for all patients, there are several barriers and ethical considerations to fertility preservation in the pediatric and adolescent female population. Additionally, the fertility preservation methods for pre- and postpubertal females differ, with only experimental methods available for prepubertal females. We will review the risk of chemotherapy and radiation on female fertility, the approach to fertility preservation in the pediatric and adolescent female population, methods of fertility preservation for both pre- and postpubertal females, barriers to fertility preservation, cost, and psychological and ethical considerations.

MicroRNAs: New Insight in Modulating Follicular Atresia: A Review

Our understanding of the post-transcriptional mechanisms involved in follicular atresia is limited; however, an important development has been made in understanding the biological regulatory networks responsible for mediating follicular atresia. MicroRNAs have come to be seen as a key regulatory actor in determining cell fate in a wide range of tissues in normal and pathological processes. Profiling studies of miRNAs during follicular atresia and development have identified several putative miRNAs enriched in apoptosis signaling pathways. Subsequent in vitro and/or in vivo studies of granulosa cells have elucidated the functional role of some miRNAs along with their molecular pathways. In particular, the regulatory roles of some miRNAs have been consistently observed during studies of follicular cellular apoptosis. Continued work should gradually lead to better understanding of the role of miRNAs in this field. Ultimately, we expect this understanding will have substantial benefits for fertility management at both the in vivo or/and in vitro levels. The stable nature of miRNA holds remarkable promise in clinical use as a diagnostic tool and in reproductive medicine to solve the ever-increasing fertility problem. In this review, we summarize current knowledge of the involvement of miRNAs in follicular atresia, discuss the challenges for further work and pinpoint areas for future research.

Cryopreservation of ovaries from neonatal marmoset monkeys

The ovary of neonatal nonhuman primates contains the highest number of immature oocytes, but its cryopreservation has not yet been sufficiently investigated in all life stages. In the current study, we investigated cryodamage after vitrification/warming of neonatal ovaries from a nonhuman primate, the common marmoset (Callithrix jacchus). A Cryotop was used for cryopreservation of whole ovaries. The morphology of the vitrified/warmed ovaries was found to be equivalent to that of fresh ovaries. No significant difference in the number of oocytes retaining normal morphology per unit area in histological sections was found between the two groups. In an analysis of dispersed cells from the ovaries, however, the cell viability of the vitrified/warmed group tended to be decreased. The results of a comet assay showed no significant differences in DNA damage. These results show that cryopreservation of neonatal marmoset ovaries using vitrification may be useful as a storage system for whole ovaries.

Roles of epidermal growth factor (EGF)-like factor in the ovulation process

Luteinizing hormone (LH) surge stimulates preovulatory follicles to induce the ovulation process, including oocyte maturation, cumulus expansion, and granulosa cell luteinization. The matured oocytes surrounded by an expanded cumulus cell layer are released from follicles to the oviduct. However, LH receptors are dominantly expressed in granulosa cells, but less in cumulus cells and are not expressed in oocytes, indicating that the secondary factors expressed and secreted from LH-stimulated granulosa cells are required for the induction of the ovulation process. Prostaglandin and progesterone are well-known factors that are produced in granulosa cells and then stimulate in both granulosa and cumulus cells. The mutant mice of prostaglandin synthase (Ptgs2KO mice) or progesterone receptor (PRKO mice) revealed that the functions were essential to accomplish the ovulation process, but not to induce the ovulation process. To identify the factors initiating the transfer of the stimuli of LH surge from granulosa cells to cumulus cells, M. Conti's lab and our group performed microarray analysis of granulosa cells and identified the epidermal growth factor (EGF)-like factor, amphiregulin (AREG), epiregulin (EREG), and β-cellulin (BTC) that act on EGF receptor (EGFR) and then induce the ERK1/2 and Ca²⁺-PLC pathways in cumulus cells. When each of the pathways was down-regulated using a pharmacological approach or gene targeting study, the induction of cumulus expansion and oocyte maturation were dramatically suppressed, indicating that both pathways are inducers of the ovulation process. However, an in vitro culture study also revealed that the EGFR-induced unphysiological activation of PKC in cumulus cells accelerated oocyte maturation with low cytostatic activity. Thus, the matured oocytes are not arrested at the metaphase II (MII) stage and then spontaneously form pronuclei. The expression of another type of EGF-like factor, neuregulin 1 (NRG1), that does not act on EGFR, but selectively binds to ErbB3 is observed in granulosa cells after the LH surge. NRG1 supports EGFR-induced ERK1/2 phosphorylation, but reduces PKC activity to physiological level in the cumulus cells, which delays the timing of meiotic maturation of oocytes to adjust the timing of ovulation. Thus, both types of EGF-like factor are rapidly induced by LH surge and then stimulate cumulus cells to control ERK1/2 and PKC pathways, which results in the release of matured oocytes with a fertilization competence.

Ethnicity or environment: effects of migration on ovarian reserve among Bangladeshi women in the United Kingdom

OBJECTIVE

To assess whether the quality of early childhood environments among different groups of Bangladeshi women, including migrants to the United Kingdom (UK), contributes to variation in ovarian reserve and the rate of reproductive aging in later life.

DESIGN

Cross-sectional study.

SETTING

Not applicable.

PATIENT(S)

A total of 179 healthy women volunteers aged 35-59 years were divided into four groups: [1] 36 Bangladeshis living in Sylhet, Bangladesh; [2] 53 Bangladeshis who migrated to the UK as adults; [3] 40 Bangladeshis who migrated to the UK as children aged 0-16 years; and [4] a reference group of 50 women of European origin living in London.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Levels of serum antimüllerian hormone, inhibin B, FSH, and E2, and anthropometrics derived from biomarkers; reproductive, demographic, and health variables from structured questionnaires.

RESULT(S)

Bangladeshi migrants who moved to the UK as children and European women had a highly significantly larger, age-related ovarian reserve compared with migrant Bangladeshis who had moved to the UK as adults or Bangladeshi women still living in Bangladesh. There were no other significant covariates in the model aside from age and menopausal status.

CONCLUSION(S)

The study points to the importance of childhood development in considering variation in ovarian reserve across different ethnic groups. Clinical studies and research in assisted reproductive technology have emphasized the role of genes or race in determining inter-population variation in ovarian reserve. Early life developmental factors should be given due consideration when evaluating inter-group differences in response to assisted reproductive technology.

An externally validated age-related model of mean follicle density in the cortex of the human ovary

Purpose

The ability to accurately estimate a woman’s ovarian reserve by non-invasive means is the goal of ovarian reserve prediction. It is not known whether a correlation exists between model-predicted estimates of ovarian reserve and data generated by direct histological analysis of ovarian tissue. The aim of this study was to compare mean non-growing follicle density values obtained from analysis of ovarian cortical tissue samples against ovarian volume models.

Methods

Non-growing follicle density values were obtained from 13 ovarian cortical biopsies (16-37 years). A mean non-growing follicle density was calculated for each patient by counting all follicles in a given volume of biopsied ovarian cortex. These values were compared to age-matched model generated densities (adjusted to take into consideration the proportion of ovary that is cortex) and the correlation between data sets tested.

Results

Non-growing density values obtained from fresh biopsied ovarian cortical samples closely matched model generated data with low mean difference, tight agreement limits and no proportional error between the observed and predicted results.

Conclusion

These findings validate the use of the adjusted population and ovarian volume models, to accurately predict mean follicle density in the ovarian cortex of healthy adult women.

The neonatal marmoset monkey ovary is very primitive exhibiting many oogonia

Oogonia are characterized by diploidy and mitotic proliferation. Human and mouse oogonia express several factors such as OCT4, which are characteristic of pluripotent cells. In human, almost all oogonia enter meiosis between weeks 9 and 22 of prenatal development or undergo mitotic arrest and subsequent elimination from the ovary. As a consequence, neonatal human ovaries generally lack oogonia. The same was found in neonatal ovaries of the rhesus monkey, a representative of the old world monkeys (Catarrhini). By contrast, proliferating oogonia were found in adult prosimians (now called Strepsirrhini), which is a group of ‘lower’ primates. The common marmoset monkey (Callithrix jacchus) belongs to the new world monkeys (Platyrrhini) and is increasingly used in reproductive biology and stem cell research. However, ovarian development in the marmoset monkey has not been widely investigated. Herein, we show that the neonatal marmoset ovary has an extremely immature histological appearance compared with the human ovary. It contains numerous oogonia expressing the pluripotency factors OCT4A, SALL4, and LIN28A (LIN28). The pluripotency factor-positive germ cells also express the proliferation marker MKI67 (Ki-67), which has previously been shown in the human ovary to be restricted to premeiotic germ cells. Together, the data demonstrate the primitiveness of the neonatal marmoset ovary compared with human. This study may introduce the marmoset monkey as a non-human primate model to experimentally study the aspects of primate primitive gonad development, follicle assembly, and germ cell biology in vivo.

Quantification of healthy and atretic germ cells and follicles in the developing and post-natal ovary of the South American plains vizcacha, Lagostomus maximus: evidence of continuous rise of the germinal reserve

The female germ line in mammals is subjected to massive cell death that eliminates 60-85% of the germinal reserve by birth and continues from birth to adulthood until the exhaustion of the germinal pool. Germ cell demise occurs mainly through apoptosis by means of a biased expression in favour of pro-apoptotic members of the BCL2 gene family. By contrast, the South American plains vizcacha, Lagostomus maximus, exhibits sustained expression of the anti-apoptotic BCL2 gene throughout gestation and a low incidence of germ cell apoptosis. This led to the proposal that, in the absence of death mechanisms other than apoptosis, the female germ line should increase continuously from foetal life until after birth. In this study, we quantified all healthy germ cells and follicles in the ovaries of L. maximus from early foetal life to day 60 after birth using unbiased stereological methods and detected apoptosis by labelling with TUNEL assay. The healthy germ cell population increased continuously from early-developing ovary reaching a 50 times higher population number by the end of gestation. TUNEL-positive germ cells were <0.5% of the germ cell number, except at mid-gestation (3.62%). Mitotic proliferation, entrance into prophase I stage and primordial follicle formation occurred as overlapping processes from early pregnancy to birth. Germ cell number remained constant in early post-natal life, but a remnant population of non-follicular VASA- and PCNA-positive germ cells still persisted at post-natal day 60. L. maximus is the first mammal so far described in which female germ line develops in the absence of constitutive massive germ cell elimination.

Polymorphisms in gonadotropin and gonadotropin receptor genes as markers of ovarian reserve and response in in vitro fertilization

Since gonadotropins are the fundamental hormones that control ovarian activity, genetic polymorphisms may alter gonadal responsiveness to glycoproteins; hence they are important regulators of hormone activity at the target level. The establishment of the pool of primordial follicles takes place during fetal life and is mainly under genetic control. Consequently, single nucleotide polymorphisms (SNPs) in gonadotropins and their receptors do not seem to be associated with any significant modification in the endowment of nongrowing follicles in the ovary. Indeed, the age at menopause, a biological characteristic strongly related to ovarian reserve, as well as markers of functional ovarian reserve such as anti-Müllerian hormone and antral follicle count, are not different in women with different genetic variants. Conversely, some polymorphisms in FSH receptor (FSHR) seem to be associated with modifications in ovarian activity. In particular, studies suggest that the Ser680 genotype for FSHR is a factor of relative resistance to FSH stimulation resulting in slightly higher FSH serum levels, thus leading to a prolonged duration of the menstrual cycle. Moreover, some FSHR gene polymorphisms show a positive association with ovarian response to exogenous gonadotropin administration, hence exhibiting some potential for a pharmacogenetic estimation of the FSH dosage in controlled ovarian stimulation. The study of SNPs of the FSHR gene is an interesting field of research that could provide us with new information about the way each woman responds to exogenous gonadotropin administration during ovulation induction.

The infant and pubertal human ovary: Balbiani's body-associated VASA expression, immunohistochemical detection of apoptosis-related BCL2 and BAX proteins, and DNA fragmentation

STUDY QUESTION

How do apoptosis-related BCL2 and BAX genes, known to regulate death or survival of germ cells in fetal and adult life, and germ-cell-specific VASA protein behave from birth to puberty in the human ovary?

SUMMARY ANSWER

In resting primordial follicles in both infant and pubertal ovaries, BCL2 family members and germ-cell-specific VASA behave as in fetal life. After birth, once follicles leave the resting reserve to enter the growing follicular pool, detection of apoptosis-related genes moves from the germ cell to granulosa cells and VASA expression is lost.

WHAT IS KNOWN ALREADY

In the human ovary, around 85% of the 7 × 10⁶ potential oocytes produced at mid-gestation are lost before birth, an extra 10% before puberty, and loss continues throughout reproductive life until germinal exhaustion of the ovary. Oocyte loss is mainly driven through a balanced expression of BCL2 gene family members. Apoptosis-inducing BAX gene shows a sustained expression throughout fetal and adult life, whereas apoptosis-inhibiting BCL2 is detectable during the proliferative stage of primordial germ cells and oogonia in the fetal ovary and proliferation of granulosa cells in growing follicles in the adult ovary. The germ-cell marker VASA is detectable in the fetal ovary from early oogenesis and is conspicuously expressed in primordial follicles, where in late pregnancy it is associated with the Balbiani's vitelline space. VASA expression is not detectable in the adult ovary.

STUDY DESIGN, SIZE, DURATION

This is a qualitative analysis involving infant/pubertal paraffin-embedded human ovaries screened for apoptosis-related proteins, DNA fragmentation and germ-cell identity.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ovaries from 13 patients ranging in age from 4 to 16 years, undergoing gynaecological surgical procedures due to benign pathology, were studied. Tissues were fixed in 10% formalin, paraffin-embedded and processed for immunohistochemistry to screen the temporal and cellular localization of germ-cell-specific VASA protein and BCL2 and BAX apoptosis-related proteins. In addition, a terminal deoxynucleotidyl transferase-mediated deoxiuridinetriphosphate nick-end labelling (TUNEL) assay was performed to detect DNA fragmentation. General histology and tissue integrity were assessed by haematoxylin-eosin staining.

MAIN RESULTS AND THE ROLE OF CHANCE

VASA showed a differential pattern of expression; in the resting primordial follicle reserve in infant and pubertal ovaries, it was associated with the Balbiani's body space in the germ cell. VASA remained detectable in primary follicles leaving the resting reserve, but once follicles entered the growing pool it became undetectable. This pattern of VASA expression is the same as in the fetal ovary. BAX was expressed both in the resting primordial reserve and in the pool of growing follicles, whereas BCL2 was detected only in granulosa cells in antral follicles in the growing pool. Apoptosis-related protein expression moved from the germ cell to the somatic stratum when primordial follicles left the resting reserve to enter the pool of growing follicles, irrespective of female age. Most TUNEL-positive cells were detected in the granulosa cells of antral follicles. No TUNEL-positive cells were found in resting primordial follicles.

LIMITATIONS, REASONS FOR CAUTION

The study was limited by the qualitative nature of the immuno-histochemical analysis and the TUNEL assay. The results neither quantify the levels of germ-cell death nor exclude other concurrent cell death mechanisms that could act in the regulation of female germ-cell number.

WIDER IMPLICATIONS OF THE FINDING

This study provides missing knowledge about apoptosis and germ-cell-specific VASA expression in the human ovary between birth and puberty and the participation of BCL2 and BAX genes in the balance between death and survival throughout female germ-line development. Intracellular localization of VASA in resting follicles emerges as a possible marker with prognostic value that needs further investigation, especially in infant patients entering ovarian cryo-preservation programmes. This knowledge will be valuable in optimizing the rescue and clinical use of germ cells to restore fertility in women.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was obtained for this study. The authors have no conflicts of interest to declare.

Dexamethasone induces germ cell apoptosis in the human fetal ovary

CONTEXT

The 21-hydroxylase deficiency is the most common cause of congenital adrenal hyperplasia. Pregnant women presenting a risk of genetic transmission may be treated with synthetic glucocorticoids such as dexamethasone (DEX) to prevent female fetus virilization.

OBJECTIVE

The aim of this study was to assess the potential deleterious effects of DEX exposure on fetal ovarian development.

SETTINGS

Human fetal ovaries, ranging from 8-11 weeks after fertilization, were harvested from material available after legally induced abortions. They were cultured in the absence or presence of DEX (2, 10, or 50 μm) over 14 d, and histological analyses were performed.

RESULTS

The glucocorticoid receptor NR3C1 was present and the signaling pathway active in the fetal ovary as demonstrated by the expression of NR3C1 target genes, such as PLZF and FKBP5, in response to DEX exposure. DEX decreased germ cell density at the 10 and 50 μm doses. Exposure to DEX, even at the highest dose, did not change oogonial proliferation as monitored by 5-bromo-2'-deoxyuridine incorporation and significantly increased the apoptotic rate, detected with cleaved caspase 3 staining. Interestingly, the expression of the prosurvival gene KIT was significantly decreased in the presence of DEX during the course of the culture.

CONCLUSION

We have demonstrated for the first time that in vitro exposure to high doses of DEX impairs human fetal oogenesis through an increase in apoptosis. These data are of high importance, and additional epidemiological studies are required to investigate the female fertility of those women who have been exposed to DEX during fetal life.

Variation in ovarian follicle density during human fetal development

PURPOSE

To obtain a precise estimate of ovarian follicle density and variation in the number of follicles at several gestational ages during human fetal development.

METHODS

Twelve necropsied ovaries from 9 fetuses (gestational age: 24 to 36 weeks) and 3 neonates (who died within the first hours of life) were studied. Ovaries were fixed with 4 % formaldehyde and embedded in paraffin. Serial, 7 mm thick sections of the ovaries were cut and evaluated at every 50 cuts. Follicles were counted in 10 regions (each measuring 625 μm(2)) of the ovarian cortex and the number of follicles per mm³ was calculated.

RESULTS

The number of follicles per 0.25 mm² ranged from 10.9 (± 4.8) in a neonate to 34.7 (± 10.6) also in a neonate. Among fetuses, follicle density was lowest at 36 weeks of gestation (11.1 ± 6.2) and highest at 26 weeks (32 ± 8.9). The total number of follicles ranged from 500,000 at the age of 22 weeks to > 1,000,000 at the age of 39 weeks.

CONCLUSION

Our results show a peak in the number of follicles during intrauterine life at approximately 26 weeks, followed by a rapid reduction in this number before birth, providing a step forward towards the understanding of primordial follicular assembly in humans and, ultimately, the identification of the determinants of reproductive capacity.

Ovarian tissue cryopreservation for fertility preservation in cancer patients: successful establishment and feasibility of a multidisciplinary collaboration

BACKGROUND

As advancements in cancer therapies have led to dramatic improvements in long term survival, there has been increasing interest in methods to expand fertility preservation options for cancer patients.

METHODS

An experimental protocol for ovarian tissue cryopreservation was developed at the University of Pennsylvania for patients requiring gonadotoxic therapies. The protocol for adults was implemented at the Hospital of the University of Pennsylvania and for children at the Children's Hospital of Philadelphia in collaboration with the Oncofertility Consortium and the National Physicians Cooperative (NPC).

RESULTS

A total of twenty-one patients (age range: 8-36 years) have cryopreserved ovarian tissue as part of this study. While patients had a variety of diagnoses and treatment exposures, 10/21 (48 %) patients suffered from hematologic disorders and 43 % were anticipating stem cell transplantation. No patients have requested that the tissue be used for clinical purposes.

CONCLUSIONS

Ovarian tissue cryopreservation protocols can be implemented at pediatric and adult institutions through multi-disciplinary collaboration. While more research is needed to determine the safety and efficacy of ovarian tissue cryopreservation, this procedure provides hope for preserving the ability to have biological offspring to patients facing gonadotoxic therapies for a variety of medical conditions.

The ovarian follicular pool and reproductive outcome in women

Both quantitative and qualitative aspects of the ovarian reserve are inversely related to age, hence the relationship existing between low quantity and low quality may be only indirect and depending on their strong relationship with the third variable, namely women's age. However the possibility exists that they may also be directly related. The objective of this study was to investigate the relationship between ovarian reserve and female reproductive outcome. Eight published studies reporting histological data on the human ovaries have been carefully reviewed. Only studies where the reproductive history of women was reported have been included for the analysis. The non-growing follicle count was plotted versus age and the best fit line through the data was calculated. All patients were assigned as to be above or below the calculated median hence differentiating women with high or low ovarian reserve for their age. A similar number of pregnancies ended in miscarriage in women with low and high ovarian reserve. The number of deliveries per woman in both the groups was not statistically different. The results of the study do not support the hypothesis that quality and quantity of the follicular pool are directly related.

NCI, NHLBI/PBMTC first international conference on late effects after pediatric hematopoietic cell transplantation: endocrine challenges-thyroid dysfunction, growth impairment, bone health, & reproductive risks

The endocrine system is highly susceptible to damage by high-dose chemotherapy and/or irradiation before hematopoietic cell transplantation (HCT) during childhood. The specific endocrine organs most affected by HCT include the thyroid gland, the pituitary, and the gonads. In addition, hormones that support development and stability of the skeletal system are also affected. Insufficiency of thyroid hormone is 1 of the most common late sequelae of HCT, and occurs more often in young children. Deficiency in the pituitary's production of growth hormone is a problem of unique concern to the pediatric population. The reproductive risks of HCT depend on the patient's gender and pubertal status at the time of HCT. Pubertal or gonadal failure frequently occurs, especially in females. Infertility risks for both genders remain high, whereas methods of fertility preservation are limited in all but postpubertal males. Bone health post-HCT can be compromised by low bone mineral density as well as avascular necrosis, but the data on both problems in the pediatric HCT population are limited. In this paper, the current state of knowledge, gaps in that knowledge, and recommendations for future research are addressed in detail for each of these systems.

Morphological and morphometric parameters of human ovaries from embryonic to menopausal age

Background:

There is a relationship between the intrauterine development, pubertal and adulthood variations, anomalies, and pathology of ovaries. But the entire development spectrum of the ovaries from fetal to menopausal age has not been examined among Indian females.

Objectives:

This study was conducted with an objective to establish the morphological and morphometric development characteristics of ovaries in local population as a proxy for Indians.

Materials and Methods:

Thirty ovaries from prenatal embryos and fetuses aged 6 weeks to 40 weeks and 50 postnatal ovaries up to 55 years of age were studied for morphology and morphometry, by doing dissection.

Results:

Oval shape was predominant in prenatal ovaries (66.68%), followed by rod (20%), almond, and “S” shapes (6.66% each). Among the postnatal ovaries while almond shape accounted for 72%, the incidence of oval shape was 28%. There was a significant correlation between gestational age and weight of the ovaries both in prenatal (r = 0.56) and postnatal (r = 0.696) specimens studied.

Conclusion:

Variations in the morphological and morphometric development characteristics of ovaries are common. The findings of this study form an initial database for the local population which may be improved in the subsequent studies.

Generation of viable embryos and embryonic stem cell-like cells from cultured primary follicles in mice

Primary follicles retrieved from B6CBAF1 prepubertal mice were cultured in a stepwise manner in an alpha-minimum essential medium-based medium to generate viable embryos and embryonic stem cell (ESC)-like cells. A significant increase in follicle growth and oocyte maturation accompanied by increased secretion of 17beta-estradiol and progesterone was achieved by exposing primary follicles to 100 or 200 mIU of follicle-stimulating hormone (FSH) during culture. More oocytes developed into blastocysts following in vitro fertilization (IVF) or parthenogenetic activation after culture with 200 mIU of FSH during the entire culture period than with 100 mIU. Eleven ESC-like cell lines, consisting of four heterozygotic and seven homozygotic phenotypes, were established from 25 trials of primary follicle culture combined with IVF or parthenogenetic activation. In conclusion, primary follicles can potentially yield developmentally competent oocytes, which produce viable embryos and ESC-like cell lines following in vitro manipulation. We suggest a method to utilize immature follicles, which are most abundant in ovaries, to improve reproductive efficiency and for use in regenerative medicine.

The developing ovary of the South American plains vizcacha, Lagostomus maximus (Mammalia, Rodentia): massive proliferation with no sign of apoptosis-mediated germ cell attrition

Apoptosis-dependent massive germ cell death is considered a constitutive trait of the developing mammalian ovary that eliminates 65–85% of the germinal tissue depending on the species. After birth and during adult lifetime, apoptotic activity moves from the germ cell proper to the somatic compartment, decimating germ cells through follicular atresia until the oocyte reserve is exhausted. In contrast, the South American rodent Lagostomus maximus shows suppressed apoptosis-dependent follicular atresia in the adult ovary, with continuous folliculogenesis and massive polyovulation, which finally exhausts the oocyte pool. The absence of follicular atresia in adult L. maximus might arise from a failure to move apoptosis from the germinal stratum to the somatic compartment after birth or being a constitutive trait of the ovarian tissue with no massive germ cell degeneration in the developing ovary. We tested these possibilities by analysing oogenesis, expression of germ cell-specific VASA protein, apoptotic proteins BCL2 and BAX, and DNA fragmentation by TUNEL assay in the developing ovary of L. maximus. Immunolabelling for VASA revealed a massive and widespread colonisation of the ovary and proliferation of germ cells organised in nests that disappeared at late development when folliculogenesis began. No sign of germ cell attrition was found at any time point. BCL2 remained positive throughout oogenesis, whereas BAX was slightly detected in early development. TUNEL assay was conspicuously negative throughout the development. These results advocate for an unrestricted proliferation of germ cells, without apoptosis-driven elimination, as a constitutive trait of L. maximus ovary as opposed to what is normally found in the developing mammalian ovary.

Systemic signals in aged males exert potent rejuvenating effects on the ovarian follicle reserve in mammalian females

Through the use of parabiosis in mice, aging-related deterioration of skeletal muscle and liver has been linked to a loss of systemic factors that support adult stem or progenitor cell activity. Since aging-related ovarian failure has recently been attributed, at least in part, to a loss of de-novo oocyte-containing follicle formation associated with declining oogonial stem cell activity, herein we tested in mice if aging-related changes in systemic factors influence the size of the ovarian follicle reserve. Ovaries of young (2-month-old) females parabiotically joined with young females for 5 weeks possess comparable numbers of healthy and degenerative (atretic) oocyte-containing follicles in their ovaries as those detected in non-parabiotic young females. Joining of young females with young males significantly increases follicle atresia without a net change healthy follicle numbers. Surprisingly, young females joined with aged (24-month-old) males exhibit a significant increase in the number of primordial follicles comprising the ovarian reserve, and this occurs without changes in follicle growth activation or atresia. Blood of aged males also induces ovarian expression of the germ cell-specific meiosis gene, Stimulated by retinoic acid gene 8 (Stra8), in ovaries of female parabionts, further supporting the conclusion that the observed changes in the follicle reserve of females joined with aged males reflect increased oocyte formation. Thus, factors in male blood exert dramatic effects on ovarian follicle dynamics, and aging males possess a beneficial systemic factor that significantly expands the ovarian follicle reserve in females through enhanced oogenesis.

Genes involved in initial follicle recruitment may be associated with age at menopause

CONTEXT

Timing of menopause is largely influenced by genetic factors. Because menopause occurs when the follicle pool in the ovaries has become exhausted, genes involved in primordial follicle recruitment can be considered as candidate genes for timing of menopause.

OBJECTIVE

The aim was to study the association of 23 tagging single nucleotide polymorphisms in five genes [Anti-Müllerian hormone (AMH), AMH type II receptor (AMHR2), bone morphogenetic protein 15 (BMP15), forkhead transcription factor L2 (FOXL2), and growth differentiation factor-9 (GDF9)] involved in recruitment of the primary follicle pool, including the AMHR2 gene, which has recently been associated with age at menopause.

DESIGN

We conducted a cross-sectional association study.

SETTING AND PARTICIPANTS

We studied a population-based sample of 3616 Dutch women with natural menopause.

MAIN OUTCOME MEASURE

We measured age at natural menopause.

RESULTS

Both studied AMHR2 tagging single nucleotide polymorphisms (rs2002555 and rs11170547) in the AMHR2 gene were associated with age at natural menopause in interaction with parity. Parous rs2002555 G/G carriers had menopause 1 yr later compared with A/A carriers (P = 0.01). For rs11170547, each minor allele (T) was associated with a 0.41-yr later onset of menopause in parous women (P = 0.01). Additionally, rs6521896 in BMP15 was associated with later menopause (β = 0.41; P = 0.007). Variants in the AMH, FOXL2, and GDF9 genes were not associated with timing of menopause.

CONCLUSIONS

The present study confirms an earlier finding that variation in the AMHR2 gene modifies the relation between parity and age at natural menopause. In combination with the association of BMP15 with menopausal age, we find that there is evidence that genes involved in primary follicle recruitment influence timing of menopause.

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.

Genetically modified mouse models for premature ovarian failure (POF)

Premature ovarian failure (POF) is a complex disorder that affects approximately 1% of women. POF is characterized by the depletion of functional ovarian follicles before the age of 40 years, and clinically, patients may present with primary amenorrhea or secondary amenorrhea. Although some genes have been hypothesized to be candidates responsible for POF, the etiology of most of the cases is idiopathic, with the underlying causes still unidentified because of the heterogeneity of the disease. In this review, we consider some mutant mouse models that exhibit phenotypes which are comparable to human POF, and we suggest that the use of these mouse models may help us to gain a better understanding of the molecular mechanisms underlying POF in humans.

Molecular mechanisms underlying the activation of mammalian primordial follicles

In humans and other mammalian species, the pool of resting primordial follicles serves as the source of developing follicles and fertilizable ova for the entire length of female reproductive life. One question that has intrigued biologists is: what are the mechanisms controlling the activation of dormant primordial follicles. Studies from previous decades have laid a solid, but yet incomplete, foundation. In recent years, molecular mechanisms underlying follicular activation have become more evident, mainly through the use of genetically modified mouse models. As hypothesized in the 1990s, the pool of primordial follicles is now known to be maintained in a dormant state by various forms of inhibitory machinery, which are provided by several inhibitory signals and molecules. Several recently reported mutant mouse models have shown that a synergistic and coordinated suppression of follicular activation provided by multiple inhibitory molecules is necessary to preserve the dormant follicular pool. Loss of function of any of the inhibitory molecules for follicular activation, including PTEN (phosphatase and tensin homolog deleted on chromosome 10), Foxo3a, p27, and Foxl2, leads to premature and irreversible activation of the primordial follicle pool. Such global activation of the primordial follicle pool leads to the exhaustion of the resting follicle reserve, resulting in premature ovarian failure in mice. In this review, we summarize both historical and recent results on mammalian primordial follicular activation and focus on the up-to-date knowledge of molecular networks controlling this important physiological event. We believe that information obtained from mutant mouse models may also reflect the molecular machinery responsible for follicular activation in humans. These advances may provide a better understanding of human ovarian physiology and pathophysiology for future clinical applications.

Variation in the ovarian reserve is linked to alterations in intrafollicular estradiol production and ovarian biomarkers of follicular differentiation and oocyte quality in cattle

The mechanisms whereby the high variation in numbers of morphologically healthy oocytes and follicles in ovaries (ovarian reserve) may have an impact onovarian function, oocyte quality, and fertility are poorly understood. The objective was to determine whether previously validated biomarkers for follicular differentiation and function, as well as oocyte quality differed between cattle with low versus a high antral follicle count (AFC). Ovaries were removed (n = 5 per group) near the beginning of the nonovulatory follicular wave, before follicles could be identified via ultrasonography as being dominant, from heifers with high versus a low AFC. The F1, F2, and F3 follicles were dissected and diameters determined. Follicular fluid and thecal, granulosal, and cumulus cells and the oocyte were isolated and subjected to biomarker analyses. Although the size and numerous biomarkers of differentiation, such as mRNAs for the gonadotropin receptors, were similar, intrafollicular concentrations of estradiol and the abundance of mRNAs for CYP19A1 in granulosal cells and ESR1, ESR2, and CTSB in cumulus cells were greater, whereas mRNAs for AMH in granulosal cells and TBC1D1 in thecal cells were lower for animals with low versus a high AFC during follicle waves. Hence, variation in the ovarian reserve may have an impact on follicular function and oocyte quality via alterations in intrafollicular estradiol production and expression of key genes involved in follicle-stimulating hormone action (AMH) and estradiol (CYP19A1) production by granulosal cells, function and survival of thecal cells (TBC1D1), responsiveness of cumulus cells to estradiol (ESR1, ESR2), and cumulus cell determinants of oocyte quality (CTSB).

Effects of tea polyphenols on ovarian development in rats

Tea is the most consumed beverage in the world. Tea polyphenols are the major constituents of tea leaves and have shown many potential healthy benefits. However, whether tea polyphenols influence ovarian follicle assembly and development and ovarian life span is unknown. To study the effect of tea polyphenols on ovarian follicle development and oocyte apoptosis, we investigated rat ovarian development of different ages [from postnatal day (PD)1 after birth to 10 months] after treatment with tea polyphenols. Our data showed that the percentage of unassembled follicles increased in the ovaries of 1- and 2-day-old rats which were ip injected with tea polyphenols (50 mg/kg/d) or whose mothers were treated with tea polyphenols (100 mg/kg/d) by intragastric administration from the day 11 after the detection of vaginal plug till delivery. The percentage of primordial follicles increased, while that of developing follicles decreased in the ovaries of 4- and 8-day-old rats following peritoneal injection with tea polyphenols compared with controls. The ratio of terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL)-positive oocytes decreased in the ovaries of neonatal rats following tea polyphenol treatment. In the 3- and 10-month-old rat ovaries, the number of primordial follicles augmented, whereas that of atretic follicles decreased after the treatment for 4 weeks. These data suggest that tea polyphenols may inhibit the transition from primordial to developing follicles, extend the entire growth phase of a follicle, and reduce dominant follicle numbers per cycle to increase the reserve of germ cells, inhibit oocyte apoptosis and follicle atresia during ovarian development from birth to early aged, and retard climacterium in rats. Drinking even a small cup of tea per day may benefit to extent the productive life of ovary.