Workflow Optimization for Identification of Female Germline or Oogonial Stem Cells in Human Ovarian Cortex Using Single-Cell RNA Sequence Analysis

In 2004, the identification of female germline or oogonial stem cells (OSCs) that can support post-natal oogenesis in ovaries of adult mice sparked a major paradigm shift in reproductive biology. Although these findings have been independently verified, and further extended to include identification of OSCs in adult ovaries of many species ranging from pigs and cows to non-human primates and humans, a recent study rooted in single-cell RNA sequence analysis (scRNA-seq) of adult human ovarian cortical tissue claimed that OSCs do not exist, and that other groups working with OSCs following isolation by magnetic-assisted or fluorescence-activated cell sorting have mistaken perivascular cells (PVCs) for germ cells. Here we report that rare germ lineage cells with a gene expression profile matched to OSCs but distinct from that of other cells, including oocytes and PVCs, can be identified in adult human ovarian cortical tissue by scRNA-seq after optimization of analytical workflow parameters. Deeper cell-by-cell expression profiling also uncovered evidence of germ cells undergoing meiosis-I in adult human ovaries. Lastly, we show that, if not properly controlled for, PVCs can be inadvertently isolated during flow cytometry protocols designed to sort OSCs because of inherently high cellular autofluorescence. However, human PVCs and human germ cells segregate into distinct clusters following scRNA-seq due to non-overlapping gene expression profiles, which would preclude the mistaken identification and use of PVCs as OSCs during functional characterization studies.

Protecting life in a time of war

Despite centuries of lessons from history, war endures. Across Earth, during nearly every year from the beginning of the twentieth century to present day, over 30 wars have been fought resulting in 187 million casualties, excluding the most recent conflict, which is the impetus for this essay (Timeline of 20th and 21st century wars). We are, sadly, a war-mongering people. The word “war” word infiltrates our vernacular, e.g., the war on poverty, on drugs, on cancer, on COVID, and, apropos, on terror. How did rational approaches to disagreement and conflict evade the world’s progress? Reproductive physicians and scientists are dedicated to safeguard lives and build families. Violence is antithetical to our mission as professionals, and moral integrity as humans. We are deeply concerned for, and stand in unity with, our Ukrainian colleagues—the embryologists, scientists, OBGYN and REI physicians, infertility patients, and all people under siege. Reproductive health services for Ukrainians (as with many other war-torn regions) have collapsed. Deeply disturbing reports have emerged that cite civilian hospitals (including maternity centers) being targeted. Liquid nitrogen supplies are scarce. Pregnant mothers and gestational carriers are at emergent risk of delivering in extremely harsh conditions, cold underground bunkers and refugee queues.

In vitro growth and maturation of primordial follicles and immature oocytes

Cryopreservation of ovarian tissue to preserve the fertility of girls and young women at high risk of sterility is now widely practiced. Pieces of cryopreserved ovarian cortex can be thawed and autografted to restore fertility, but because of the risks of reintroduction of the cancer, transplantation may not be possible for girls and women with blood-borne leukemias or cancers with a high risk of ovarian metastasis. Cryopreserved ovarian tissue contains mainly primordial follicles but also provides access to immature oocytes from small antral follicles, which may be matured in vitro to provide an additional source of mature oocytes. So in cases in which transplantation is contraindicated, fertility restoration could be safely achieved in the laboratory either by in vitro maturation (IVM) of oocytes aspirated from growing follicles or by the complete in vitro growth (IVG) and maturation (IVM) of primordial follicles to produce fertile metaphase II (MII) oocytes. The development of IVM and IVG methods to support all stages of oocytes available within ovarian tissue will maximize the potential for all patients undergoing fertility preservation.

FERTILITY PRESERVATION: Progress and prospects for developing human immature oocytes in vitro

Ovarian cryopreservation rapidly developed from basic science to clinical application and can now be used to preserve the fertility of girls and young women at high risk of sterility. Primordial follicles can be cryopreserved in ovarian cortex for long-term storage and subsequently autografted back at an orthotopic or heterotopic site to restore fertility. However, autografting carries a risk of re-introducing cancer cells in patients with blood-born leukaemias or cancers with a high risk of ovarian metastasis. For these women fertility restoration could only be safely achieved in the laboratory by the complete in vitro growth (IVG) and maturation (IVM) of cryopreserved primordial follicles to fertile metaphase II (MII) oocytes. Culture systems to support the development of human oocytes have provided greater insight into the process of human oocyte development as well as having potential applications within the field of fertility preservation. The technology required to culture human follicles is extremely challenging, but significant advances have been made using animal models and translation to human. This review will detail the progress that has been made in developing human in vitro growth systems and consider the steps required to progress this technology towards clinical application.

Inhibition of PTEN activates bovine non-growing follicles in vitro but increases DNA damage and reduces DNA repair response

STUDY QUESTION

Does ovarian follicle activation by phosphatase homologue of chromosome-10 (PTEN) inhibition affect DNA damage and repair in bovine oocytes and granulosa cells?

SUMMARY ANSWER

PTEN inhibition promotes bovine non-growing follicle activation but results in increased DNA damage and impaired DNA repair capacity in ovarian follicles in vitro.

WHAT IS KNOWN ALREADY

Inhibition of PTEN is known to activate primordial follicles but may compromise further developmental potential. In breast cancer cells, PTEN inhibition represses nuclear translocation of breast cancer susceptibility 1 (BRCA1) and Rad51; this impairs DNA repair resulting in an accumulation of damaged DNA, which contributes to cell senescence.

STUDY DESIGN, SIZE, DURATION

Bovine ovarian tissue fragments were exposed to control medium alone or containing either 1 or 10 μM bpv(HOpic), a pharmacological inhibitor of PTEN, in vitro for 24 h. A sub-group of tissue fragments were collected for Western blot analysis after bpv(HOpic) exposure. The remainder were incubated in control medium for a further 5 days and then analysed histologically and by immunohistochemistry to detect DNA damage and repair pathways.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Bovine ovaries were obtained from abattoir-slaughtered heifers. Tissue fragments were exposed to either control medium alone or medium containing either 1 μM or 10 μM bpv(HOpic) for 24 h. Tissue fragments collected after 24 h were subjected to Akt quantification by Western blotting (six to nine fragments per group per experiment). Follicle stage and morphology were classified in remaining fragments. Immunohistochemical analysis included nuclear exclusion of FOXO3 as a marker of follicle activation, γH2AX as a marker of DNA damage, meiotic recombination 11 (MRE11), ataxia telangiectasia mutated (ATM), Rad51, breast cancer susceptibility 1 (BRCA1) and breast cancer susceptibility 2 (BRCA2) as DNA repair factors. A total of 29 550 follicles from three independent experiments were analysed.

MAIN RESULTS AND THE ROLE OF CHANCE

Tissue fragments exposed to bpv(HOpic) had increased Akt phosphorylation at serine 473 (pAkt/Akt ratio, 2.25- and 6.23-fold higher in 1 and 10 μM bpv(HOpic) respectively compared to control, P < 0.05). These tissue fragments contained a significantly higher proportion of growing follicles compared to control (78.6% in 1 μM and 88.7% in 10 μM versus 70.5% in control; P < 0.001). The proportion of morphologically healthy follicles did not differ significantly between 1 μM bpv(HOpic) and control (P < 0.001) but follicle health was lower in 10 μM compared to 1 μM and control in all follicle types (P < 0.05). DNA damage in oocytes, indicated by expression of γH2AX, increased following exposure to 1 μM bpv(HOpic) (non-growing, 83%; primary follicles, 76%) and 10 μM (non-growing, 77%; primary, 84%) compared to control (non-growing, 30% and primary, 59%) (P < 0.05 for all groups). A significant reduction in expression of DNA repair proteins MRE11, ATM and Rad51 was observed in oocytes of non-growing and primary follicles of treatment groups (primary follicles in controls versus 10 μM bpv(HOpic): MRE, 68% versus 47%; ATM, 47% versus 18%; Rad51, 48% versus 24%), P < 0.05 for all groups. Higher dose bpv(HOpic) also resulted in lower expression of BRCA1 compared to control and 1 μM bpv(HOpic) (P < 0.001) in non-growing and primary follicles. BRCA2 expression was increased in oocytes of primary follicles in 1 μM bpv(HOpic) (36%) compared to control (20%, P = 0.010) with a marked decrease in 10 μM (1%, P ≤ 0.001). Granulosa cells of primary and secondary follicles in bpv(HOpic) groups showed more DNA damage compared to control (P < 0.05). However, bpv(HOpic) did not impact granulosa cell DNA repair capacity in secondary follicles, but BRCA1 declined significantly in higher dose bpv(HOpic).

LARGE-SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This study focuses on non-growing follicle activation after 6 days culture and may not reflect DNA damage and repair capacity in later stages of oocyte and follicle growth.

WIDER IMPLICATIONS OF THE FINDINGS

In vitro activation of follicle growth may compromise the bidirectional signalling between oocyte and granulosa cells necessary for optimal oocyte and follicle health. This large animal model may be useful in optimising follicle activation protocols with a view to transfer for clinical application.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by Indonesia endowment fund for education. No competing interest.

TRIAL REGISTRATION NUMBER

Not applicable.

Crosstalk between PTEN/PI3K/Akt Signalling and DNA Damage in the Oocyte: Implications for Primordial Follicle Activation, Oocyte Quality and Ageing

The preservation of genome integrity in the mammalian female germline from primordial follicle arrest to activation of growth to oocyte maturation is fundamental to ensure reproductive success. As oocytes are formed before birth and may remain dormant for many years, it is essential that defence mechanisms are monitored and well maintained. The phosphatase and tensin homolog of chromosome 10 (PTEN)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB, Akt) is a major signalling pathway governing primordial follicle recruitment and growth. This pathway also contributes to cell growth, survival and metabolism, and to the maintenance of genomic integrity. Accelerated primordial follicle activation through this pathway may result in a compromised DNA damage response (DDR). Additionally, the distinct DDR mechanisms in oocytes may become less efficient with ageing. This review considers DNA damage surveillance mechanisms and their links to the PTEN/PI3K/Akt signalling pathway, impacting on the DDR during growth activation of primordial follicles, and in ovarian ageing. Targeting DDR mechanisms within oocytes may be of value in developing techniques to protect ovaries against chemotherapy and in advancing clinical approaches to regulate primordial follicle activation.

In vitro growth of immature bovine follicles and oocytes

The limitation in the supply of mature, fertilisable oocytes constitutes a major impediment to increasing the success of assisted reproduction, stem cell derivation and cloning in domestic species. Techniques are being developed to grow immature oocytes invitro that have the potential to increase the supply of oocytes. Mouse oocytes can be cultured from initial stages of development to maturity, and live young have been produced, but for domestic species, such as cows, with long growth periods, invitro systems that allow complete growth of oocytes contained within primordial follicles to maturity is technically challenging and has not yet been achieved. For cows, several culture systems have been developed that support specific developmental stages, but a multistep culture system will be required for complete growth invitro. This review highlights the steps that will be required to achieve the goal of growing oocytes invitro.

Extracellular Localisation of the C-Terminus of DDX4 Confirmed by Immunocytochemistry and Fluorescence-Activated Cell Sorting

Putative oogonial stem cells (OSCs) have been isolated by fluorescence-activated cell sorting (FACS) from adult human ovarian tissue using an antibody against DEAD-box helicase 4 (DDX4). DDX4 has been reported to be germ cell specific within the gonads and localised intracellularly. White et al. (2012) hypothesised that the C-terminus of DDX4 is localised on the surface of putative OSCs but is internalised during the process of oogenesis. This hypothesis is controversial since it is assumed that RNA helicases function intracellularly with no extracellular expression. To determine whether the C-terminus of DDX4 could be expressed on the cell surface, we generated a novel expression construct to express full-length DDX4 as a DsRed2 fusion protein with unique C- and N-terminal epitope tags. DDX4 and the C-terminal myc tag were detected at the cell surface by immunocytochemistry and FACS of non-permeabilised human embryonic kidney HEK 293T cells transfected with the DDX4 construct. DDX4 mRNA expression was detected in the DDX4-positive sorted cells by RT-PCR. This study clearly demonstrates that the C-terminus of DDX4 can be expressed on the cell surface despite its lack of a conventional membrane-targeting or secretory sequence. These results validate the use of antibody-based FACS to isolate DDX4-positive putative OSCs.

Characterization of follicles in girls and young women with Turner syndrome who underwent ovarian tissue cryopreservation

OBJECTIVE

To characterize ovarian follicles of girls and young women with Turner syndrome (TS) who underwent ovarian tissue cryopreservation (OTC).

DESIGN

Retrospective case-control study.

SETTING

University hospital.

PATIENT(S)

Fifteen girls and young women with TS aged 5-22 years at OTC were included, together with 42 control girls and young women aged 1-25 years who underwent OTC because of cancer.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Follicle density (follicles/mm³), morphology, and health were assessed in ovarian cortex biopsies from TS patients and compared with controls. Hormone concentrations were measured in serum and follicle fluids. Immature cumulus oocyte complexes were obtained and matured in vitro.

RESULT(S)

Follicles were found in 60% of the biopsies (9 of 15) from TS ovaries. In 78% of the ovaries (7 of 9) with follicles, the follicle density was within the 95% confidence interval of the control group. There was a high rate of abnormal follicle morphology. Six follicle-specific proteins were expressed similarly in TS and control ovaries. However, apoptosis and zona pellucida protein expression were found to be abnormal in TS. Turner syndrome follicle fluid from small antral follicles had lower concentrations of estrogen and testosterone and higher concentrations of antimüllerian hormone than controls. Thirty-one cumulus oocyte complexes were collected from one patient and cultured for 48 hours in vitro, resulting in five metaphase II oocytes (maturation rate 16%, degeneration rate 19%).

CONCLUSION(S)

The benefits of OTC may be limited to a highly selected group of TS mosaic patients in whom a sizeable pool of normal follicles is present at OTC.

Metaphase II oocytes from human unilaminar follicles grown in a multi-step culture system

STUDY QUESTION

Can complete oocyte development be achieved from human ovarian tissue containing primordial/unilaminar follicles and grown in vitro in a multi-step culture to meiotic maturation demonstrated by the formation of polar bodies and a Metaphase II spindle?

SUMMARY ANSWER

Development of human oocytes from primordial/unilaminar stages to resumption of meiosis (Metaphase II) and emission of a polar body was achieved within a serum free multi-step culture system.

WHAT IS KNOWN ALREADY

Complete development of oocytes in vitro has been achieved in mouse, where in vitro grown (IVG) oocytes from primordial follicles have resulted in the production of live offspring. Human oocytes have been grown in vitro from the secondary/multi-laminar stage to obtain fully grown oocytes capable of meiotic maturation. However, there are no reports of a culture system supporting complete growth from the earliest stages of human follicle development through to Metaphase II.

STUDY DESIGN, SIZE, DURATION

Ovarian cortical biopsies were obtained with informed consent from women undergoing elective caesarean section (mean age: 30.7 ± 1.7; range: 25-39 years, n = 10).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Laboratory setting. Ovarian biopsies were dissected into thin strips, and after removal of growing follicles were cultured in serum free medium for 8 days (Step 1). At the end of this period secondary/multi-laminar follicles were dissected from the strips and intact follicles 100-150 μm in diameter were selected for further culture. Isolated follicles were cultured individually in serum free medium in the presence of 100 ng/ml of human recombinant Activin A (Step 2). Individual follicles were monitored and after 8 days, cumulus oocyte complexes (COCs) were retrieved by gentle pressure on the cultured follicles. Complexes with complete cumulus and adherent mural granulosa cells were selected and cultured in the presence of Activin A and FSH on membranes for a further 4 days (Step 3). At the end of Step 3, complexes containing oocytes >100 μm diameter were selected for IVM in SAGE medium (Step 4) then fixed for analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

Pieces of human ovarian cortex cultured in serum free medium for 8 days (Step 1) supported early follicle growth and 87 secondary follicles of diameter 120 ± 6 μm (mean ± SEM) could be dissected for further culture. After a further 8 days, 54 of the 87 follicles had reached the antral stage of development. COCs were retrieved by gentle pressure from the cultured follicles and those with adherent mural granulosa cells (n = 48) were selected and cultured for a further 4 days (Step 3). At the end of Step 3, 32 complexes contained oocytes >100 μm diameter were selected for IVM (Step 4). Nine of these complexes contained polar bodies within 24 h and all polar bodies were abnormally large. Confocal immuno-histochemical analysis showed the presence of a Metaphase II spindle confirming that these IVG oocytes had resumed meiosis but their developmental potential is unknown.

LIMITATIONS, REASONS FOR CAUTION

This is a small number of samples but provides proof of concept that complete development of human oocytes can occur in vitro. Further optimization with morphological evaluation and fertilization potential of IVG oocytes is required to determine whether they are normal.

WIDER IMPLICATIONS OF THE FINDINGS

The ability to develop human oocytes from the earliest follicular stages in vitro through to maturation and fertilization would benefit fertility preservation practice.

STUDY FUNDING/COMPETING INTEREST(S)

Funded by MRC Grants (G0901839 and MR/L00299X/1). No competing interests.

The existence and potential of germline stem cells in the adult mammalian ovary

It has long been accepted that the complement of follicles within the ovary is formed before birth in humans, or shortly after birth in rodents, and that no follicles are formed thereafter. This follows entry of all oogonia into meiosis in fetal life, with no remaining germ stem cells in the ovary, in contrast to the presence of spermatogonia in the testis. This has been brought back into debate in recent years, following the demonstration of isolation of cells expressing both germline and stem markers from the postnatal ovary in several species, including humans. We describe these cells as putative ovarian stem cells. Isolation of these cells is challenging, adding to the debate as to their existence, and the validity of DDX4 as the main marker used for their isolation has also to be questioned. While different groups have used varying techniques and indeed terminology to describe these cells, the body of evidence regarding their initial characterization after isolation is growing. There remain very limited data regarding their developmental potential, but the demonstration of the production of functional oocytes from induced pluripotent stem cells and the advances in ovarian follicle culture techniques provide a basis for such studies.

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.

Being a good egg in the 21st century

INTRODUCTION

Women are increasingly having children at a later age, but this can conflict with declining fertility in the later 30's and thereafter.

AREAS OF AGREEMENT

Declining egg quality and quantity with age are well-established, although egg quality can only be surmised from reproductive success or failure.

AREAS OF CONTROVERSY

Whether increasing the number of eggs that can be obtained from ovarian stimulation is of value, and whether there are precursor cells within the adult ovary that could become mature eggs.

GROWING POINTS

There is increasing use of donated eggs by older women to enhance their chances of conception. The storage of frozen eggs for potential use later in life is also becoming more common.

AREAS TIMELY FOR DEVELOPING RESEARCH

Understanding of growth initiation of follicles and development of an artificial ovary may lead to the ability to affect fertility and reproductive lifespan.

Initial characterisation of adult human ovarian cell populations isolated by DDX4 expression and aldehyde dehydrogenase activity

The existence of a population of putative stem cells with germline developmental potential (oogonial stem cells: OSCs) in the adult mammalian ovary has been marked by controversy over isolation methodology and potential for in-vitro transformation, particularly where cell sorting has been based on expression of DEAD box polypeptide 4 (DDX4). This study describes a refined tissue dissociation/fluorescence-activated cell sorting (FACS) protocol for the ovaries of adult women which results in increased cell viability and yield of putative OSCs. A FACS technique incorporating dual-detection of DDX4 with aldehyde dehydrogenase 1 (ALDH1) demonstrates the existence of two sub-populations of small DDX4-positive cells (approx. 7 µm diameter) with ALDH1 activity, distinguished by expression of differentially spliced DDX4 transcripts and of DAZL, a major regulator of germ cell differentiation. These may indicate stages of differentiation from a progenitor population and provide a likely explanation for the expression disparities reported previously. These findings provide a robust basis for the further characterisation of these cells, and exploration of their potential physiological roles and therapeutic application.

Non-growing follicle density is increased following adriamycin, bleomycin, vinblastine and dacarbazine (ABVD) chemotherapy in the adult human ovary

STUDY QUESTION

Do the chemotherapeutic regimens of ABVD (adriamycin, bleomycin, vinblastine and dacarbazine) or OEPA-COPDAC (combined vincristine, etoposide, prednisone, doxorubicin (OEPA) and cyclophosphamide, vincristine, prednisone, dacarbazine (COPDAC)) used to treat Hodgkin lymphoma (HL), affect the density, morphology and in vitro developmental potential of human ovarian follicles?

SUMMARY ANSWER

Ovarian tissue from women treated with ABVD contained a higher density of non-growing follicles (NGFs) per cubic millimetre and increased numbers of multiovular follicles but showed reduced in vitro growth compared with patients with lymphoma who had not received chemotherapy, patients treated with OEPA-COPDAC, age-matched healthy women and age-related model-predicted values.

WHAT IS KNOWN ALREADY

Chemotherapy regimens can cause a loss of follicles within the ovary, which depends on the drugs given. Early stage HL is commonly treated by ABVD, a non-alkylating regimen that apparently has ovarian sparing qualities; thus it is important to investigate the histological appearance and distribution of follicles within ABVD-treated ovarian tissue.

STUDY DESIGN, SIZE, DURATION

Thirteen ovarian biopsies were obtained from HL patients (six adolescents and seven adults) and one biopsy from a non-HL patient. Two HL patients and the non-HL patient had received no treatment prior to biopsy collection. The remaining 11 HL patients received one of two regimens: ABVD or OEPA-COPDAC. Tissue was analysed histologically and compared to biopsies from healthy women, and in a subgroup of patients, tissue was cultured for 6 days in vitro.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ovarian biopsies were obtained from patients undergoing ovarian cryopreservation for fertility preservation and from healthy women at the time of Caesarian section ('obstetric tissue'). Follicle number and maturity were evaluated in sections of ovarian cortical tissue, and compared to an age-related model of mean follicle density and to age-matched contemporaneous biopsies. The developmental potential of follicles was investigated after 6 days of tissue culture.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 6877 follicles were analysed. ABVD-treated tissue contained a higher density of NGFs per cubic millimetre (230 ± 17) (mean ± SEM) than untreated (110 ± 54), OEPA-COPDAC-treated (50 ± 27) and obstetric (20 ± 4) tissue (P < 0.01), with follicle density 9-21 SD higher than predicted by an age-related model. Biovular and binucleated NGFs occurred frequently in ABVD-treated and in adolescent-untreated tissue but were not observed in OEPA-COPDAC-treated or obstetric tissue, although OEPA-COPDAC-treated tissue contained a high proportion of morphologically abnormal oocytes (52% versus 23% in untreated, 22% in ABVD-treated and 25% in obstetric tissue; P < 0.001). Activation of follicle growth in vitro occurred in all groups, but in ABVD-treated samples there was very limited development to the secondary stage, whereas in untreated samples from lymphoma patients growth was similar to that observed in obstetric tissue (untreated; P < 0.01 versus ABVD-treated, NS versus obstetric).

LARGE SCALE DATA

N/A LIMITATIONS, REASONS FOR CAUTION: Although a large number of follicles were analysed, these data were derived from a small number of biopsies. The mechanisms underpinning these observations have yet to be determined and it is unclear how they relate to future fertility.

WIDER IMPLICATIONS OF THE FINDINGS

This study confirms that the number of NGFs is not depleted following ABVD treatment, consistent with clinical data that female fertility is preserved. Our findings demonstrate that immature follicle density can increase as well as decrease following at least one chemotherapy treatment. This is the first report of morphological and follicle developmental similarities between ABVD-treated tissue and the immature human ovary. Further experiments will investigate the basis for the marked increase in follicle density in ABVD-treated tissue.

STUDY FUNDING/COMPETING INTERESTS

Funded by UK Medical Research Council Grants G0901839 and MR/L00299X/1. The authors have no competing interests.

Re-implantation of cryopreserved ovarian cortex resulting in restoration of ovarian function, natural conception and successful pregnancy after haematopoietic stem cell transplantation for Wilms tumour

With the improvement of long-term cancer survival rates, growing numbers of female survivors are suffering from treatment-related premature ovarian insufficiency (POI). Although pre-treatment embryo and oocyte storage are effective fertility preservation strategies, they are not possible for pre-pubertal girls or women who cannot delay treatment. In these cases, the only available treatment option is ovarian cortex cryopreservation and subsequent re-implantation. A 32-year-old woman had ovarian cortex cryopreserved 10 years previously before commencing high-dose chemotherapy and undergoing a haematopoietic stem cell transplant for recurrent adult Wilms tumour, which resulted in POI. She underwent laparoscopic orthotopic transplantation of cryopreserved ovarian cortex to the original site of biopsy on the left ovary. She ovulated at 15 and 29 weeks post-re-implantation with AMH detectable, then rising, from 21 weeks, and conceived naturally following the second ovulation. The pregnancy was uncomplicated and a healthy male infant was born by elective Caesarean section at 36⁺⁴ weeks gestation. This is the first report of ovarian cortex re-implantation in the UK. Despite the patient receiving low-risk chemotherapy prior to cryopreservation and the prolonged tissue storage duration, the re-implantation resulted in rapid restoration of ovarian function and natural conception with successful pregnancy.

New approaches to increasing oocyte yield from ruminants

Artificial insemination, superovulation and embryo transfer have had beneficial impacts on animal production but a limiting factor to realizing the full potential of these techniques and of other reproductive technologies is the availability of fertile oocytes. To overcome this problem, methods for maturing oocytes in vitro (IVM) have been developed. The production of bovine embryos by IVM is in commercial use but the rate of success and quality of embryos is low. The lack of success may be due to the quality of oocytes that are being matured and it would be preferable to utilize the abundant source of immature oocytes from preantral and primordial follicles by developing systems for in vitro growth (IVG). Several culture systems that utilize early growing follicles as a source of oocytes have been developed for laboratory species and these have been successful in producing live young. IVG in association with IVM and cryopreservation have the potential to maximize the genetic potential of high genetic merit females and shorten generation intervals. This paper presents the current status of technology for the in vitro growth and development of immature oocytes, in vitro maturation and cryopreservation of germ cells in domestic ruminants.

Factors affecting folliculogenesis in ruminants

This review addresses the reasons for the lack of progress in the control of superovulation and highlights the importance of understanding the mechanisms underlying follicular development. The present inability to provide large numbers of viable embryos from selected females still restricts genetic improvement, whilst variability in ovarian response to hormones limit the present capacity for increasing reproductive efficiency.

Females are born with a large store of eggs which rapidly declines as puberty approaches. If these oocytes are normal then there is scope for increasing the reproductive potential of selected females. Oocytes must reach a certain size before they can complete all stages of development and the final changes that occur late in follicular development. It is likely that oocytes that do not produce specific factors at precise stages of development will not be viable. Hence, it is important to characterize oocyte secreted factors since there are potential indicators of oocyte quality.

The mechanisms that determine ovulation rate have still not been fully elucidated. Indeed follicular atresia, the process whereby follicles regress, is still not known. A better understanding of these processes should prove pivotal for the synchronization of follicular growth, for more precise oestrous synchronization and improved superovulatory response.

Nutrition can influence a whole range of reproductive parameters however, the pathways through which nutrition acts have not been fully elucidated. Metabolic hormones, particularly insulin and IGFs, appear to interact with gonadotrophins at the level of the gonads. Certainly gonadotropins provide the primary drive for the growth of follicles in the later stages of development and both insulin and IGF-1, possibly IGF-2, synergize with gonadotrophins to stimulate cell proliferation and hormone production. More research is required to determine the effects of other growth factors and their interaction with gonadotropins.

There is evidence, particularly from studies with rodents, that steroids can also modulate follicular growth and development, although information is very limited for ruminants. There may be a rôle for oestrogens in synchronizing follicular waves, to aid in oestrous synchronization regimes and for removing the dominant follicle to achieve improved superovulatory responses. However more information is required to determine whether these are feasible approaches.

Heritability for litter size is higher in sheep than in cattle. Exogenous gonadotropins are a commercially ineffective means of inducing twinning in sheep and cattle. Although there are differences in circulating gonadotropin concentrations, the mechanism(s) responsible for the high ovulation appear to reside essentially within the ovaries. The locus of the Booroola gene, a major gene for ovulation rate, has been established but not specifically identified. However sheep possessing major genes do provide extremely valuable models for investigating the mechanisms controlling ovulation rate, including a direct contrast to mono-ovulatory species such as cattle.

In conclusion, the relationship between oocyte quality, in both healthy follicles and those follicles destined for atresia, must be resolved before the future potential for increasing embryo yield can be predicted. In addition, a greater understanding of the factors affecting folliculogenesis in ruminants should ensure that the full benefits ensuing from the precise control of ovarian function are achieved. The improved use of artificial insemination and embryo transfer that would ensue from a greater understanding of the processes of folliculo genesis, coupled with the new technologies of genome and linkage mapping, should ensure a more rapid rate of genetic gain.

Creating a Global Community of Practice for Oncofertility

Fertility preservation in the cancer setting, known as oncofertility, is a field that requires cross-disciplinary interaction between physicians, basic scientists, clinical researchers, ethicists, lawyers, educators, and religious leaders. Funded by the National Institutes of Health, the Oncofertility Consortium (OC) was formed to be a scientifically grounded, transparent, and altruistic resource, both intellectual and monetary, for building this new field of practice capable of addressing the unique needs of young patients with cancer. The OC has expanded its attention to include other nonmalignant conditions that can threaten fertility, and the work of the OC now extends around the globe, involving partners who together have created a community of shared effort, resources, and practices. The OC creates materials that are translated, disseminated, and amended by all participants in the field, and local programs of excellence have developed worldwide to accelerate the pace and improve the quality of oncofertility research and practice. Here we review the global oncofertility programs and the capacity building activities that strengthen these research and clinical programs, ultimately improving patient care.

The controversial existence and functional potential of oogonial stem cells

The regenerative potential of the mammalian ovary has been a controversial area over the last decade. Isolation of cells, termed oogonial stem cells (OSCs), from adult rodent and human ovaries has been reported, with these cells exhibiting both germ and stem cell markers in culture. When re-introduced into an ovarian somatic environment these cells have generated follicles capable of producing healthy offspring in rodents, and there is some evidence of human OSCs being able to form oocyte-like structures in a xenotransplant model. Importantly, there are no data on their potential physiological role within the ovary, and specifically no evidence that they contribute to the primordial follicle pool and thus to later stages of follicle development. The cues required for oocyte differentiation from these cells are not well understood either in vivo or in vitro, and these will need to be further elucidated to maximise their potential for therapeutic intervention. OSCs may also be of value as a model to investigate normal human germ cell differentiation. It is likely that their interactions with ovarian somatic cells and/or extracellular signals will be important in these processes. This review summarises our current knowledge on the isolation and characterisation of mammalian oogonial stem cells.