Establishing reproductive potential and advances in fertility preservation techniques for XY individuals with differences in sex development.

BACKGROUND: Discordance between gonadal type and gender identity has often led to an assumption of infertility in patients with differences in sex development (DSD). However, there is now greater recognition of fertility being an important issue for this group of patients. Currently, gonadal tissue that may have fertility potential is not being stored for individuals with DSD and, where gonadectomy forms part of management, is often discarded. The area of fertility preservation has been predominantly driven by oncofertility which is a field dedicated to preserving the fertility of patients undergoing gonadotoxic cancer treatment. The use of fertility preservation techniques could be expanded to include individuals with DSD where functioning gonads are present. METHODS: This is a systematic literature review evaluating original research articles and relevant reviews between 1974 and 2018 addressing DSD and fertility, in vitro maturation of sperm, and histological/ultrastructural assessment of gonadal tissue in complete and partial androgen insensitivity syndrome, 17ß-hydroxysteroid dehydrogenase type 3 and 5α-reductase deficiency. CONCLUSION: Successful clinical outcomes of ovarian tissue cryopreservation are paving the way for similar research being conducted using testicular tissue and sperm. There have been promising results from both animal and human studies leading to cryopreservation of testicular tissue now being offered to boys prior to cancer treatment. Although data are limited, there is evidence to suggest the presence of reproductive potential in the gonads of some individuals with DSD. Larger, more detailed studies are required, but if these continue to be encouraging, individuals with DSD should be given the same information, opportunities and access to fertility preservation as other patient groups.

In vitro and in vivo mouse follicle development in ovaries and reaggregated ovaries.

Follicle development requires complex and coordinated interactions between both the oocyte and its associated somatic cells. In ovarian dysfunction, follicle development may be abnormal due to defective somatic cell function; for example, premature ovarian insufficiency or malignancies. Replacing defective somatic cells, using the reaggregated ovary (RO) technique, may 'rescue' follicle development. ROs containing mature follicles have been generated when transplanted to a host mouse to develop. We have developed a RO culture technique and the aims were to determine how follicle development differed between transplanted and cultured ROs, and the influence of ovarian age (P2 vs P6). Mouse ROs were cultured for 14 days; P2 and P6 ovaries cultured as Controls. Follicle development was compared to ROs transplanted for 14 days and ovaries from P16 and P20 mice. ROs generated from either P2 or P6 exhibited similar follicle development in culture whereas in vivo follicle development was more advanced in P6 ROs. Follicles were more developed in cultured ROs than transplanted ROs. However, follicles in cultured ROs and ovaries had smaller oocytes with fewer theca and granulosa cells than in vivo counterparts. Our results demonstrate the fluidity of follicle development despite ovary dissociation and that environment is more important to basal lamina formation and theca cell development. Furthermore, follicle development within cultured ROs appears to be independent of oocyte nest breakdown and primordial follicle formation in source ovaries. Our results highlight the need for understanding follicle development in vitro, particularly in the development of the RO technique as a potential fertility treatment.

Oocyte-specific ablation of N- and O-glycans alters cumulus cell signalling and extracellular matrix composition.

Cumulus-oocyte complex (COC) expansion is essential for ovulation and fertilisation and is linked to oocyte quality. Hyaluronan (HA), the major matrix constituent, is cross-linked via inter-α-inhibitor heavy chains (HCs), pentraxin 3 (PTX3) and tumour necrosis factor-stimulated gene 6 (TSG-6). All except HCs are secreted by cumulus cells in response to oocyte-secreted factors, which signal via SMAD pathways. The double mutant (DM) mouse generates oocytes lacking complex N- and O-glycans due to oocyte-specific deletion of core 1 ß1,3-galactosyltransferase (C1galt1) and N-acetylglucosaminyltransferase I (Mgat1) and has modified cumulus expansion. We compared COCs before expansion (48 h-post-pregnant mare serum gonadotrophin (PMSG)) and at late-stage expansion (9 h-post-human chorionic gonadotrophin (hCG); control n=3 mice, DM n=3 per group). Using histochemistry the levels of HA, HCs, PTX3, TSG-6 and phosphorylated-SMAD1/5/8 and -SMAD2 (12-25 COCs per group) were assessed. DM COCs did not differ from Controls in cumulus size or cell density at 9 h-post-hCG; however, HA and HC levels and phosphorylated-SMAD1/5/8 were reduced. Furthermore, no correlations were found between the levels of matrix molecules and cumulus area in DM or Control samples. These data suggest that HA and HCs can support cumulus expansion provided that they are present above minimum threshold levels. We propose that oocyte-specific ablation of C1galt1 and Mgat1 may affect bone morphogenetic protein 15 synthesis or bioactivity, thereby reducing SMAD1/5/8 phosphorylation and HA production.

Oocyte stem cells: fact or fantasy?

For many decades, the dogma prevailed that female mammals had a finite pool of oocytes at birth and this was gradually exhausted during a lifetime of reproductive function. However, in 2004, a new era began in the field of female oogenesis. A study was published that appeared to detect oocyte-stem cells capable of generating new eggs within mouse ovaries. This study was highly controversial and the years since this initial finding have produced extensive research and even more extensive debate into their possibility. Unequivocal evidence testifying to the existence of oocyte-stem cells (OSCs) has yet to be produced, meanwhile the spectrum of views from both sides of the debate are wide-ranging and surprisingly passionate. Although recent studies have presented some convincing results that germ cells exist and are capable of creating new oocytes, many questions remain. Are these cells present in humans? Do they exist in physiological conditions in a dormant state? This comprehensive review first examines where and how the dogma of a finite pool was established, how this has been challenged over the years and addresses the most pertinent questions as to the current status of their existence, their role in female fertility, and perhaps most importantly, if they do exist, how can we harness these cells to improve a woman's oocyte reserve and treat conditions such as premature ovarian insufficiency (POI: also known as premature ovarian failure, POF).

Analysis of in vitro follicle development during the onset of premature ovarian insufficiency in a mouse model.

Premature ovarian insufficiency (POI) occurs in 1% of women under 40 years of age and is predominantly idiopathic. In a transgenic mouse model of follicular POI, the Double Mutant (DM), female mice are fertile at 6 weeks of age, become infertile by 9 weeks and exhibit POI by 3 months. DM female mice generate oocytes lacking mucin O-glycans and complex N-glycans due to deletion of core 1 synthase, glycoprotein-N-acetylgalactosamine 3-ß-galactosyltransferase 1 (C1galt1) and mannoside acetylglucosaminyltransferase 1 (Mgat1) respectively (DM, C1galt1F/FMgat1F/F:ZP3Cre; Control, C1galt1F/FMgat1F/F). To determine whether DM follicle development could be improved in a controlled environment, follicles from DM and Control mice were cultured individually and follicle growth, morphology, survival and antrum formation were evaluated. DM ovaries were more rigid than Control ovaries at 3, 6 and 9 weeks, which was exacerbated with age, resulting in a failure to isolate follicles from 9 week-old DM females. DM follicles had decreased survival compared with Control follicles from females at 3 and 6 weeks of age. Furthermore, survival rate of DM follicles decreased with age between 3 and 6 weeks. DM follicles at both 3 and 6 weeks had accelerated follicle growth and altered antrum formation during the first few days of culture but, after 6 days, follicles were equivalent in size to the Controls. In conclusion, a population of DM follicles retain the potential to develop in vitro, and therefore follicle culture offers a reliable method to generate antral follicles from preantral follicles after the onset of POI in these female mice.

Oocyte glycoproteins regulate the form and function of the follicle basal lamina and theca cells.

Maintaining follicle integrity during development, whereby each follicle is a functional unit containing a single oocyte, is essential for the generation of healthy oocytes. However, the mechanisms that regulate this critical function have not been determined. In this paper we investigate the role of the oocyte in maintaining follicle development. To investigate this role, we use a mouse model with oocyte-specific deletion of C1galt1 which is required for the generation of core 1-derived O-glycans. The loss of oocyte-generated O-glycans results in the joining of follicles and the generation of Multiple-Oocyte Follicles (MOFs). The aim was to determine how Mutant follicle development is modified thus enabling follicles to join. Extracellular matrix and follicle permeability were studied using histology, immunohistochemistry and electron microscopy (EM). In ovaries containing Mutant Oocytes, the Follicle basal lamina (FBL) is altered both functionally and structurally from the primary stage onwards with Mutant follicles possessing unexpectedly thicker FBL. In Mutant ovaries, the theca cell layer is also modified with intermingling of theca between adjacent follicles. MOF function was analysed but despite increased numbers of preantral MOFs in Mutants, these do not reach the preovulatory stage after gonadotrophin stimulation. We propose a model describing how oocyte initiated changes in FBL and theca cells result in follicles joining. These data reveal new and important roles for the oocyte in follicle development and follicle integrity.

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

The number of eggs ovulated varies within and between species and is influenced by many variables. However, the regulatory mechanisms remain poorly understood. We previously demonstrated a key role for the oocyte because mice generating oocytes deficient in core 1-derived O-glycans ovulate ∼40-50% more eggs than Controls. Here we analyze the basis of this phenotype using Mutant [core 1 ß1,3-galactosyltransferase 1 (C1galt1)(FF):zona pellucida glycoprotein 3 Cre (ZP3Cre)] and Control (C1galt1(FF)) female mice. In culture, Mutant follicles exhibited delayed antrum formation [indicative of follicle stimulant hormone (FSH) dependence] and increased sensitivity to FSH. Although the Mutant estrous cycle was extended, comprehensive endocrine changes were not observed; rather FSH, LH, inhibin B, and anti-Mullerian hormone were temporally altered, revealing estrous cycle stage-specific modifications to the hypothalamic-pituitary-gonadal axis. At proestrus, when FSH levels were decreased in Mutants, ovaries contained more, smaller, preantral follicles. Mutant follicles exhibited reduced levels of apoptosis, and both B-cell lymphoma 2 (Bcl-2) and BCL-2-associated X protein (Bax) were altered compared with Controls. Mutant ovaries also had an increase in the expression ratio of growth differentiation factor 9 (GDF9):bone morphogenetic protein 15 (BMP15) at diestrus. On the basis of these data, we propose that modified oocyte glycoproteins alter GDF9:BMP15 expression modifying follicle development resulting in the generation of more follicles. Thus, the oocyte is a key regulator of follicle development and has a crucial role in determining ovulation rate.

Molecular analysis of the cumulus matrix: insights from mice with O-glycan-deficient oocytes.

During follicle development, oocytes secrete factors that influence the development of granulosa and cumulus cells (CCs). In response to oocyte and somatic cell signals, CCs produce extracellular matrix (ECM) molecules resulting in cumulus expansion, which is essential for ovulation, fertilisation, and is predictive of oocyte quality. The cumulus ECM is largely made up of hyaluronan (HA), TNF-stimulated gene-6 (TSG-6, also known as TNFAIP6), pentraxin-3 (PTX3), and the heavy chains (HCs) of serum-derived inter-α-inhibitor proteins. In contrast to other in vivo models where modified expansion impairs fertility, the cumulus mass of C1galt1 Mutants, which have oocyte-specific deletion of core 1-derived O-glycans, is modified without impairing fertility. In this report, we used C1galt1 Mutant (C1galt1(FF):ZP3Cre) and Control (C1galt1(FF)) mice to investigate how cumulus expansion is affected by oocyte-specific deletion of core 1-derived O-glycans without adversely affecting oocyte quality. Mutant cumulus-oocyte complexes (COCs) are smaller than Controls, with fewer CCs. Interestingly, the CCs in Mutant mice are functionally normal as each cell produced normal levels of the ECM molecules HA, TSG-6, and PTX3. However, HC levels were elevated in Mutant COCs. These data reveal that oocyte glycoproteins carrying core 1-derived O-glycans have a regulatory role in COC development. In addition, our study of Controls indicates that a functional COC can form provided all essential components are present above a minimum threshold level, and thus some variation in ECM composition does not adversely affect oocyte development, ovulation or fertilisation. These data have important implications for IVF and the use of cumulus expansion as a criterion for oocyte assessment.

Cloning for the Twenty-First Century and Its Place in Endangered Species Conservation.

Cloning as it relates to the animal kingdom generally refers to the production of genetically identical individuals. Because cloning is increasingly the subject of renewed attention as a tool for rescuing endangered or extinct species, it seems timely to dissect the role of the numerous reproductive techniques encompassed by this term in animal species conservation. Although cloning is typically associated with somatic cell nuclear transfer, the recent advent of additional techniques that allow genome replication without genetic recombination demands that the use of induced pluripotent stem cells to generate gametes or embryos, as well as older methods such as embryo splitting, all be included in this discussion. Additionally, the phenomenon of natural cloning (e.g., a subset of fish, birds, invertebrates, and reptilian species that reproduce via parthenogenesis) must also be pointed out. Beyond the biology of these techniques are practical considerations and the ethics of using cloning and associated procedures in endangered or extinct species. All of these must be examined in concert to determine whether cloning has a place in species conservation. Therefore, we synthesize progress in cloning and associated techniques and dissect the practical and ethical aspects of these methods as they pertain to endangered species conservation.

Cloning in action: can embryo splitting, induced pluripotency and somatic cell nuclear transfer contribute to endangered species conservation?

The term 'cloning' refers to the production of genetically identical individuals but has meant different things throughout the history of science: a natural means of reproduction in bacteria, a routine procedure in horticulture, and an ever-evolving gamut of molecular technologies in vertebrates. Mammalian cloning can be achieved through embryo splitting, somatic cell nuclear transfer, and most recently, by the use of induced pluripotent stem cells. Several emerging biotechnologies also facilitate the propagation of genomes from one generation to the next whilst bypassing the conventional reproductive processes. In this review, we examine the state of the art of available cloning technologies and their progress in species other than humans and rodent models, in order to provide a critical overview of their readiness and relevance for application in endangered animal conservation.

Rescue of follicle development after oocyte-induced ovary dysfunction and infertility in a model of POI.

The mechanisms and aetiology underlying the development of premature ovarian insufficiency (POI) are poorly understood. However, the oocyte clearly has a role as demonstrated by the Double Mutant (DM) mouse model where ovarian dysfunction (6 weeks) is followed by POI (3 months) due to oocyte-specific deletion of complex and hybrid N- and O-glycans. The ovaries of DM mice contain more primary follicles (3a stage) accompanied by fewer developing follicles, indicating a block in follicle development. To investigate this block, we first analysed early follicle development in postnatal (8-day), pre-pubertal (3-week) and post-pubertal (6-week and 3-month) DM (C1galt1 F/F Mgat1 F/F:ZP3Cre) and Control (C1galt1 F/F Mgat1 F/F) mice. Second, we investigated if transplantation of DM ovaries into a "normal" endocrine environment would restore follicle development. Third, we determined if replacing DM ovarian somatic cells would rescue development of DM oocytes. At 3-week, DM primary 3a follicles contain large oocytes accompanied by early development of a second GC layer and increased GC proliferation. At 6-week, DM primary 3a follicles contain abnormally large oocytes, accompanied with decreased GC proliferation. Transplantation of DM ovaries into a 'normal' endocrine environment did not restore normal follicle development. However, replacing somatic cells by generating reaggregated ovaries (ROs) did enable follicle development to progress and thus highlighted intra-ovarian factors were responsible for the onset of POI in DM females. Thus, these studies demonstrate oocyte-initiated altered communication between GCs and oocytes results in abnormal primary follicles which fail to progress and leads to POI.

The neonatal southern white rhinoceros ovary contains oogonia in germ cell nests.

The northern white rhinoceros is functionally extinct with only two females left. Establishing methods to culture ovarian tissues, follicles, and oocytes to generate eggs will support conservation efforts using in vitro embryo production. To the best of our knowledge, this is the first description of the structure and molecular signature of any rhinoceros, more specifically, we describe the neonatal and adult southern white rhinoceros (Ceratotherium simum simum) ovary; the closest relation of the northern white rhinoceros. Interestingly, all ovaries contain follicles despite advanced age. Analysis of the neonate reveals a population of cells molecularly characterised as mitotically active, pluripotent with germ cell properties. These results indicate that unusually, the neonatal ovary still contains oogonia in germ cell nests at birth, providing an opportunity for fertility preservation. Therefore, utilising ovaries from stillborn and adult rhinoceros can provide cells for advanced assisted reproductive technologies and investigating the neonatal ovaries of other endangered species is crucial for conservation.

Complex N-glycans are essential, but core 1 and 2 mucin O-glycans, O-fucose glycans, and NOTCH1 are dispensable, for mammalian spermatogenesis.

To identify roles in spermatogenesis for major subclasses of N- and O-glycans and Notch signaling, male mice carrying floxed C1galt1, Pofut1, Notch1 or Mgat1 alleles and a testis-specific Cre recombinase transgene were generated. T-synthase (C1GALT1) transfers Gal to generate core 1 and core 2 mucin O-glycans; POFUT1 transfers O-fucose to particular epidermal growth factor-like repeats and is essential for canonical Notch signaling; and MGAT1 (GlcNAcT-I) transfers GlcNAc to initiate hybrid and complex N-glycan synthesis. Cre recombinase transgenes driven by various promoters were investigated, including Stra8-iCre expressed in spermatogonia, Sycp1-Cre expressed in spermatocytes, Prm1-Cre expressed in spermatids, and AMH-Cre expressed in Sertoli cells. All Cre transgenes deleted floxed alleles, but efficiencies varied widely. Stra8-iCre was the most effective, deleting floxed Notch1 and Mgat1 alleles with 100% efficiency and floxed C1galt1 and Pofut1 alleles with ~80% efficiency, based on transmission of deleted alleles. Removal of C1galt1, Pofut1, or Notch1 in spermatogonia had no effect on testicular weight, histology, or fertility. However, males in which the synthesis of complex N-glycans was blocked by deletion of Mgat1 in spermatogonia did not produce sperm. Spermatogonia, spermatocytes, and spermatids were generated, but most spermatids formed giant multinucleated cells or symplasts, and apoptosis was increased. Therefore, although core 1 and 2 mucin O-glycans, NOTCH1, POFUT1, O-fucose glycans, and Notch signaling are dispensable, MGAT1 and complex N-glycans are essential for spermatogenesis.

Viability assessment for artificial gametes: the need for biomarkers of functional competency.

Assisted reproductive technology (ART) has resulted in more than 5 million births worldwide. However, mainstream ART techniques are not always successful for an estimated 30% of infertile patients in whom gametes are nonviable. Most patients would clearly prefer genetic parenthood, currently possible only via the use of donated gametes or, in future, via the clinical use of artificial gametes (AGs) incorporating parental DNA. Despite much recent progress in the derivation of AGs, significant obstacles remain. Although it is possible to create artificial cells exhibiting some of the molecular and physiological traits of human gametes, they do not yet exhibit the same level of functionality as their in vivo counterparts. Most current effort pays scant attention to confirmation of molecular integrity and clinical applicability of AGs. Here we discuss the various clinical parameters used to assess gamete and embryo viability and discuss markers of gamete function that may be used within future studies attempting to derive AGs. The use of AGs may prove controversial to some members of the general public, and, as such, there is significant need for an appropriate ethical and legal framework governing the clinical use of such cells. However, provided these issues can be successfully overcome, it is highly likely that AGs will represent powerful biological tools for reproductive science, a valuable training resource for embryologists and for potential use in the clinical treatment of human infertility.

Embryos generated from oocytes lacking complex N- and O-glycans have compromised development and implantation.

Female mice generating oocytes lacking complex N- and O-glycans (double mutants (DM)) produce only one small litter before undergoing premature ovarian failure (POF) by 3 months. Here we investigate the basis of the small litter by evaluating ovulation rate and embryo development in DM (Mgat1(F/F)C1galt1(F/F):ZP3Cre) and Control (Mgat1(F/F)C1galt1(F/F)) females. Surprisingly, DM ovulation rate was normal at 6 weeks, but declined dramatically by 9 weeks. In vitro development of zygotes to blastocysts was equivalent to Controls although all embryos from DM females lacked a normal zona pellucida (ZP) and ∼30% lacked a ZP entirely. In contrast, in vivo preimplantation development resulted in less embryos recovered from DM females compared with Controls at 3.5 days post coitum (dpc) (3.2±1.3 vs 7.0±0.6). Furthermore, only 45% of mated DM females contained embryos at 3.5 dpc. Of the preimplantation embryos collected from DM females, approximately half were morulae unlike Controls where the majority were blastocysts, indicating delayed embryo development in DM females. Post-implantation development in DM females was analysed to determine whether delayed preimplantation development affected subsequent development. In DM females at 5.5 dpc, only ∼40% of embryos found at 3.5 dpc had implanted. However, at 6.5 dpc, implantation sites in DM females corresponded to embryo numbers at 3.5 dpc indicating delayed implantation. At 9.5 dpc, the number of decidua corresponded to embryo numbers 6 days earlier indicating that all implanted embryos progress to midgestation. Therefore, a lack of complex N- and O-glycans in oocytes during development impairs early embryo development and viability in vivo leading to delayed implantation and a small litter.

A fertile future: Fertility preservation special series.

Fertility preservation is a rapidly advancing field with numerous broad applications ranging from retaining the prospect of fertility in a child with cancer to protecting an entire species from extinction. In recent years, huge strides have been made in understanding the biology of male and female reproduction in animals and humans and using this knowledge to develop strategies for fertility preservation across a range of clinical and ecological applications. This Reproduction and Fertility preservation series is composed of articles from experts on this topic and these will highlight key developments in fertility preservation and also identify the challenges that still face this exciting and relatively new field.

No evidence for age-related differences in mitochondrial RNA quality in the female germline.

Abstract: Mitochondrial quality is implicated as a contributor to declining fertility with aging. We investigated mitochondrial transcripts in oocytes and their associated cumulus cells from mice of different ages using RNA-seq. Mice aged 3 weeks, 9 weeks, and 1 year were superovulated, and 48 h later, oocyte cumulus complexes were collected by follicle puncture. We did not detect any major differences that could be attributed to aging. However, mitochondrial RNA transcripts which deviated from the consensus sequence were found at a higher frequency in cumulus cells than in their corresponding oocyte. Previous investigations have shown that variation in the sequence of mtRNA transcripts is substantial, and at least some of this can be accounted for by post-transcriptional modifications which impact base calling during sequencing. Our data would be consistent with either less post-transcriptional modification in mitochondrial RNA from oocytes than cumulus cells or with lower mtDNA mutational load. Lay summary: Women become less fertile as they age. Shortage of energy contributes to this, caused by a decline in the quality of mitochondria (the powerhouses of the cell) in the egg. Genes are the blueprint for the cell. They are made of DNA which is copied into an RNA message, or instructions, for making proteins. We counted differences in the RNA message of developing eggs and the cells that support them during development (cumulus cells). We compared the number of these differences in mice of different ages. These age groups represent mice had not reached puberty, those of prime reproductive age, and old mothers. We did not find any differences linked to the age of the mice. However, we did find differences between the egg and the cumulus cells. In most cases, there were lower levels of mutations in eggs than there were in cumulus cells.

The role of mitophagy during oocyte aging in human, mouse, and Drosophila: implications for oocyte quality and mitochondrial disease.

There is a worldwide trend for women to have their first pregnancy later in life. However, as oocyte quality declines with maternal aging, this trend leads to an increase in subfertility. The cellular mechanisms underlying this decline in oocyte competence are poorly understood. Oocyte mitochondria are the subcellular organelles that supply the energy that drives early embryogenesis, and thus their quality is critical for successful conception. Mitochondria contain their own DNA (mtDNA) and mutations in mtDNA cause mitochondrial diseases with severe symptoms, such as neurodegeneration and heart disease. Since mitochondrial function declines in tissues as humans age accompanied by an accumulation of mtDNA mutations, mtDNA is implicated as a cause of declining oocyte quality in older mothers. While this mutation load could be caused by declining accuracy of the mitochondrial replisome, age-related decline in mitochondrial quality control likely contributes, however knowledge is lacking. Mitophagy, a cellular process which specifically targets and recycles damaged mitochondria may be involved, but studies are scarce. And although assisted reproductive technologies can help older mothers, how these techniques affect the mechanisms that regulate mitochondrial and oocyte quality have not been studied. With the long-term goal of understanding the molecular mechanisms that control mitochondrial quality in the oocyte, model systems including Drosophila and mouse as well as human oocytes have been used. In this review, we explore the contribution of mitophagy to oocyte quality and the need for further systematic investigation in oocytes during maternal aging using different systems. LAY SUMMARY: Mitochondria are small parts of cells called organelles that generate the chemical energy needed for life. Hundreds of thousands of mitochondria in the developing eggs of the mother support the initial growth and development of the fertilized egg. However, due to increasingly diminished function over time, mitochondria generate less energy as we age, posing real problems for older women considering pregnancy. It is possible that this declining energy could be responsible for declining fertility as women age. Energy may decline because mitochondria fail and the cell's way of keeping them healthy become less efficient as we age. This review summarizes what is known about mitochondrial quality control in developing eggs as they age. In the future, understanding how the best mitochondria are selected and maintained in the egg, and hence the future baby, may enable older women with or without mitochondrial problems, to have healthy children.

Analysing culture methods of frozen human ovarian tissue to improve follicle survival.

In vitro follicle growth is a potential fertility preservation method for patients for whom current methods are contraindicated. Currently, this method has only been successful using fresh ovarian tissue. Since many patients who may benefit from this treatment currently have cryopreserved ovarian tissue in storage, optimising in vitro follicle growth (IVG) for cryopreserved-thawed tissue is critical. This study sought to improve the first step of IVG by comparing different short-term culture systems for cryopreserved-thawed human ovarian tissue, in order to yield a higher number of healthy multilayer follicles. We compared two commonly used culture media (αMEM and McCoy's 5A), and three plate conditions (300 µL, 1 mL on a polycarbonate membrane and 1 mL in a gas-permeable plate) on the health and development of follicles after 6 days of culture. A total of 5797 follicles from three post-pubertal patients (aged 21.3 ± 2.3 years) were analysed across six different culture conditions and non-cultured control. All culture systems supported follicle development and there was no difference in developmental progression between the different conditions tested. Differences in follicle morphology were evident with follicles cultured in low volume conditions having significantly greater odds of being graded as morphologically normal compared to other conditions. Furthermore, culture in a low volume of αMEM resulted in the highest proportion of morphologically normal primary and multilayer follicles (23.8% compared to 6.3-19.9% depending on condition). We, therefore, recommend culturing cryopreserved human ovarian tissue in a low volume of αMEM to support follicle health and development. LAY SUMMARY: Ovaries contain a large number of follicles, each containing an immature egg and other important cells. Cancer treatments can lead to long-lasting negative side effects to the ovaries including the destruction of follicles, resulting in infertility. One strategy to preserve fertility is freezing of ovaries or ovarian tissue in girls and women undergoing cancer treatment. The long-term aim is to thaw and grow their ovarian tissue in the laboratory to obtain mature eggs, which can then be fertilised. In this study, we compared six different methods of growing previously frozen human ovarian tissue in order to best support follicle growth and health. We found that using the lowest amount of αMEM medium (a specific type of nutrient-rich growth solution) resulted in the highest proportion of healthy follicles. Improving the methods used to grow ovarian tissue, particularly frozen tissue, is important for future fertility preservation.

Variation in follicle health and development in cultured cryopreserved ovarian cortical tissue: a study of ovarian tissue from patients undergoing fertility preservation.

This study investigated how follicle health and development in human ovarian tissue cryopreserved for fertility preservation varied between patients before and after 6 d of in vitro culture. Ovarian tissue from 12 patients (9-25 years) was used. In 3 patients, a 1hr neutral red (NR) incubation was used to identify tissues with viable follicles. Tissues were fixed, sectioned and follicles staged and graded for health. Inter-patient differences were observed in the non-cultured tissue in the number of both healthy follicles (p = 0.005) and growing follicles (p = 0.005). After culture there was significant variation in the number of transitional, primary and secondary follicles between patients (p < 0.001). Asymmetric primary follicles with a single complete layer of granulosa cells plus two or more additional partial layers were 5.5 times more likely to be observed in cultured compared to non-cultured tissue (p = 0.0063). Non-cultured (p = 0.0125) and cultured (p < 0.001) tissue selected using NR had more healthy follicles compared to tissue not selected using NR. Non-cultured and cultured tissue selected using NR had more healthy follicles compared to tissue not selected using NR (p = 0.0125; p < 0.001). We demonstrate that inter-patient variation exists in the health and development of follicles before and after culture. Culture systems need to be optimized to support cryopreserved ovarian tissue and these findings should prompt researchers to consider patient variation when evaluating culture systems.