Making gametes from alternate sources of stem cells: past, present and future

The Evolutionary Route of in vitro Human Spermatogenesis: What is the Next Destination?

Malfunction in spermatogenesis due to genetic diseases, trauma, congenital disorders or gonadotoxic treatments results in infertility in approximately 7% of males. The behavior of spermatogonial stem cells (SSCs) within three-dimensional, multifactorial, and dynamic microenvironment implicates a niche that serves as a repository for fertility, since can serve as a source of mature and functional male germ cells. Current protocols enable reprogramming of mature somatic cells into induced pluripotent stem cells (iPSCs) and their limited differentiation to SSCs within the range of 0-5%. However, the resulting human iPSC-derived haploid spermatogenic germ cell yield in terms of number and functionality is currently insufficient for transfer to infertility clinic as a therapeutic tool. In this article, we reviewed the evolution of experimental culture platforms and introduced a novel iPSCs-based approach for in vitro spermatogenesis based on a niche perspective bearing cellular, chemical, and physical factors that provide the complex arrangement of testicular seminiferous tubules embedded within a vascularized stroma. We believe that bioengineered organoids supported by smart bio-printed tubules and microfluidic organ-on-a-chip systems offer efficient, precise, personalized platforms for autologous pluripotent stem cell sources to undergo the spermatogenetic cycle, presenting a promising tool for infertile male patients with complete testicular aplasia.

Cellular remodeling and JAK inhibition promote zygotic gene expression in the Ciona germline

Transcription control is a major determinant of cell fate decisions in somatic tissues. By contrast, early germline fate specification in numerous vertebrate and invertebrate species relies extensively on RNA-level regulation, exerted on asymmetrically inherited maternal supplies, with little-to-no zygotic transcription. However delayed, a maternal-to-zygotic transition is nevertheless poised to complete the deployment of pre-gametic programs in the germline. Here, we focus on early germline specification in the tunicate Ciona to study zygotic genome activation. We first demonstrate that a peculiar cellular remodeling event excludes localized postplasmic Pem-1 mRNA, which encodes the general inhibitor of transcription. Subsequently, zygotic transcription begins in Pem-1-negative primordial germ cells (PGCs), as revealed by histochemical detection of elongating RNA Polymerase II, and nascent Mef2 transcripts. In addition, we uncover a provisional antagonism between JAK and MEK/BMPRI/GSK3 signaling, which controls the onset of zygotic gene expression, following cellular remodeling of PGCs. We propose a 2-step model for the onset of zygotic transcription in the Ciona germline and discuss the significance of germ plasm dislocation and remodeling in the context of developmental fate specification.

Very small embryonic-like stem cells have the potential to win the three-front war on tissue damage, cancer, and aging

The concept of dedifferentiation and reprogramming of mature somatic cells holds much promise for the three-front "war" against tissue damage, cancer, and aging. It was hoped that reprogramming human somatic cells into the induced pluripotent state, along with the use of embryonic stem cells, would transform regenerative medicine. However, despite global efforts, clinical applications remain a distant dream, due to associated factors such as genomic instability, tumorigenicity, immunogenicity, and heterogeneity. Meanwhile, the expression of embryonic (pluripotent) markers in multiple cancers has baffled the scientific community, and it has been suggested that somatic cells dedifferentiate and "reprogram" into the pluripotent state in vivo to initiate cancer. It has also been suggested that aging can be reversed by partial reprogramming in vivo. However, better methods are needed; using vectors or Yamanaka factors in vivo, for example, is dangerous, and many potential anti-aging therapies carry the same risks as those using induced pluripotent cells, as described above. The present perspective examines the potential of endogenous, pluripotent very small embryonic-like stem cells (VSELs). These cells are naturally present in multiple tissues; they routinely replace diseased tissue and ensure regeneration to maintain life-long homeostasis, and they have the ability to differentiate into adult counterparts. Recent evidence suggests that cancers initiate due to the selective expansion of epigenetically altered VSELs and their blocked differentiation. Furthermore, VSEL numbers have been directly linked to lifespan in studies of long- and short-lived transgenic mice, and VSEL dysfunction has been found in the ovaries of aged mice. To conclude, a greater interest in VSELs, with their potential to address all three fronts of this war, could be the "light at the end of the tunnel."

Proteomic Analysis of Murine Bone Marrow Very Small Embryonic-like Stem Cells at Steady-State Conditions and after In Vivo Stimulation by Nicotinamide and Follicle-Stimulating Factor Reflects their Germ-Lineage Origin and Multi Germ Layer Differentiation Potential

Very small embryonic-like stem cells (VSELs) are a dormant population of development early stem cells deposited in adult tissues that as demonstrated contribute to tissue/organ repair and regeneration. We postulated developmental relationship of these cells to migrating primordial germ cells (PGCs) and explained the quiescent state of these cells by the erasure of differently methylated regions (DMRs) at some of the paternally imprinted genes involved in embryogenesis. Recently, we reported that VSELs began to proliferate and expand in vivo in murine bone marrow (BM) after exposure to nicotinamide (NAM) and selected pituitary and gonadal sex hormones. In the current report, we performed proteomic analysis of VSELs purified from murine bone marrow (BM) after repeated injections of NAM + Follicle-Stimulating Hormone (FSH) that in our previous studies turned out to be an effective combination to expand these cells. By employing the Gene Ontology (GO) resources, we have performed a combination of standard GO annotations (GO-CAM) to produce a network between BM steady-state conditions VSELs (SSC-VSELS) and FSH + NAM expanded VSELs (FSH + NAM VSELs). We have identified several GO biological processes regulating development, organogenesis, gene expression, signal transduction, Wnt signaling, insulin signaling, cytoskeleton organization, cell adhesion, inhibiting apoptosis, responses to extra- and intracellular stimuli, protein transport and stabilization, protein phosphorylation and ubiquitination, DNA repair, immune response, and regulation of circadian rhythm. We report that VSELs express a unique panel of proteins that only partially overlapped with the proteome of BM - derived hematopoietic stem cells (HSCs) and hematopoietic mononuclear cells (MNCs) and respond to FSH + NAM stimulation by expressing proteins involved in the development of all three germ layers. Thus, our current data supports further germ-lineage origin and multi germ layer differentiation potential of these cells.

Co-culture induces expression of female primordial germ cell-specific genes in human Wharton's jelly-derived mesenchymal stem cells

OBJECTIVE

To detect mRNA and protein expression of meiosis-specific genes in human umbilical cord mesenchymal stem cells (hUMSCs) in an in vitro co-culture microenvironment with mouse primordial germ cells (PGCs), and to further explore the effective potential of hUMSCs to differentiate into PGCs.

METHODS

HUMSCs were obtained from human Wharton's jelly fragments by adherent culture. PGCs were derived from 12.5 days post-coitum (dpc) BalbC mice. Then hUMSCs were co-cultured with PGCs in Matrigel, inside or outside of a culture chamber, respectively. The changes in morphology and cytogenetic characteristics were observed. SCP3 and DDX4 expression in hUMSCs were detected and analyzed using immunofluorescence staining. Oct-4, Stra8, Zp3 and Dmc1 gene expressions in PGCs, hUMSCs, and hUMSCs after co-culture with PGCs were analyzed by real time reverse transcription-polymerase chain reaction.

RESULTS

Both hUMSCs and PGCs expressed Oct-4 at different degrees. After co-culture with PGCs, hUMSCs became rounded and showed AKP activity. HUMSCs suspension-cultured in Matrigel or adherent cultured with cell chamber significantly expressed Stra8, DMC1, SCP3 and DDX4 genes.

CONCLUSION

HUMSCs can be induced to express PGC-specific genes Stra8 and DMC1, spermatogonium/oogonium-specific genes SCP3 and DDX4 that predict directed differentiation potential into early germ cells at a molecular level.

Stem Cells and Organs-on-chips: New Promising Technologies for Human Infertility Treatment

Having biological children remains an unattainable dream for most couples with reproductive failure or gonadal dysgenesis. The combination of stem cells with gene editing technology and organ-on-a-chip models provides a unique opportunity for infertile patients with impaired gametogenesis caused by congenital disorders in sex development or cancer survivors. But how will these technologies overcome human infertility? This review discusses the regenerative mechanisms, applications, and advantages of different types of stem cells for restoring gametogenesis in infertile patients, as well as major challenges that must be overcome before clinical application. The importance and limitations of in vitro generation of gametes from patient-specific human-induced pluripotent stem cells (hiPSCs) will be discussed in the context of human reproduction. The potential role of organ-on-a-chip models that can direct differentiation of hiPSC-derived primordial germ cell-like cells to gametes and other reproductive organoids is also explored. These rapidly evolving technologies provide prospects for improving fertility to individuals and couples who experience reproductive failure.

Female germline stem cells: aging and anti-aging

The delay of ovarian aging and the fertility preservation of cancer patients are the eternal themes in the field of reproductive medicine. Acting as the pacemaker of female physiological aging, ovary is also considered as the principle player of cancer, cardiovascular diseases, cerebrovascular diseases, neurodegenerative diseases and etc. However, its aging mechanism and preventive measures are still unclear. Some researchers attempt to activate endogenous ovarian female germline stem cells (FGSCs) to restore ovarian function, as the most promising approach. FGSCs are stem cells in the adult ovaries that can be infinitely self-renewing and have the potential of committed differention. This review aims to elucidate FGSCs aging mechanism from multiple perspectives such as niches, immune disorder, chronic inflammation and oxidative stress. Therefore, the rebuilding nichs of FGSCs, regulation of immune dysfunction, anti-inflammation and oxidative stress remission are expected to restore or replenish FGSCs, ultimately to delay ovarian aging.

In vitro gametogenesis: A benefit for women at advanced and very advanced age? An ethical perspective

Assisted reproductive technologies (ART) may be supplemented with in vitro gametogenesis (IVG). Although IVG is still experimental the question arises whether IVG offers any moral advantages compared to implemented methods. The aim of the paper is to present the landscape of ethical arguments in favour or against IVG. ART-related ethical issues in relation to reproductive autonomy, health risks for the woman and foetus, the welfare of the future child, the adverse effects of advanced motherhood, gender equality, and justice are similar for IVG, oocyte cryopreservation, and oocyte donation. IVG may have the following advantages: (I) the psychological and physical burden of stimulation and puncture of the oocyte could be avoided; (II) women do not necessarily have to cope with motherhood at young age; (III) ethical doubts associated with oocyte donation would be eliminated; (IV) by using IVG in combination with preimplantation diagnostics, it is more likely to find suitable oocytes or embryos to increase the probability of pregnancy; (V) women would have the opportunity to decide how many oocytes should be generated and how often an attempt should be made to achieve pregnancy. Simultaneously, however, the advent of IVG may lead to new moral disadvantages: pressure on women to give birth at an advanced age or pressure on women to follow 'male' career structures. Additionally, the reimbursement of costs related to IVG is an open question, especially if equal opportunities regarding motherhood are linked to demands for equal access to ART. An early discussion about the ethical, legal, and social consequences for IVG is necessary.

Research Advances in Gametogenesis and Embryogenesis Using Pluripotent Stem Cells

The previous studies of human gametogenesis and embryogenesis have left many unanswered questions, which hinders the understanding of the physiology of these two vital processes and the development of diagnosis and treatment strategies for related diseases. Although many results have been obtained from animal studies, particularly mouse research, the results cannot be fully applied to humans due to species differences in physiology and pathology. However, due to ethical and material limitations, the direct study of human gametes and embryos is very difficult. The emergence and rapid development of organoids allow the construction of organoid systems that simulate gametogenesis and embryogenesis in vitro, and many studies have successfully established organoid systems for some parts of or even the entire processes of gametogenesis and embryogenesis. These studies typically start with the establishment of mouse models and then modify these models to obtain human organoid models. These organoid models can be used to obtain a better understanding of the signaling pathways, molecular mechanisms, genetics, and epigenetic changes involved in gametogenesis and embryogenesis and could also be applied to clinical applications, such as drug screening. Here, we discuss the formation of primordial stem cell-like cells (PGCLCs), and in vitro-induced gametes and embryoids using pluripotent stem cells (PSCs). We also analyze their applications and limitations.

Overview of follicle stimulating hormone and its receptors in reproduction and in stem cells and cancer stem cells

Follicle stimulating hormone (FSH) and its receptor (FSHR) have been reported to be responsible for several physiological functions and cancers. The responsiveness of stem cells and cancer stem cells towards the FSH-FSHR system make the function of FSH and its receptors more interesting in the context of cancer biology. This review is comprised of comprehensive information on FSH-FSHR signaling in normal physiology, gonadal stem cells, cancer cells, and potential options of utilizing FSH-FSHR system as an anti-cancer therapeutic target.

Epigenetic Modifications at the Center of the Barker Hypothesis and Their Transgenerational Implications

Embryo/fetal nutrition and the environment in the reproductive tract influence the subsequent risk of developing adult diseases and disorders, as formulated in the Barker hypothesis. Metabolic syndrome, obesity, heart disease, and hypertension in adulthood have all been linked to unwanted epigenetic programing in embryos and fetuses. Multiple studies support the conclusion that environmental challenges, such as a maternal low-protein diet, can change one-carbon amino acid metabolism and, thus, alter histone and DNA epigenetic modifications. Since histones influence gene expression and the program of embryo development, these epigenetic changes likely contribute to the risk of adult disease onset not just in the directly affected offspring, but for multiple generations to come. In this paper, we hypothesize that the effects of parental nutritional status on fetal epigenetic programming are transgenerational and warrant further investigation. Numerous studies supporting this hypothesis are reviewed, and potential research techniques to study these transgenerational epigenetic effects are offered.

Translating Basic Research to Animal Agriculture

Procedures to maintain viability of mammalian gametes and embryos in vitro, including cryopreservation, have been exceedingly valuable for my research over the past 55 years. Keeping sperm viable in vitro enables artificial insemination, which, when combined with selective breeding, often is the most effective approach to making rapid genetic change in a population. Superovulation and embryo transfer constitute a parallel approach for amplifying reproduction of female mammals. More recent developments include sexing of semen, in vitro fertilization, cloning by nuclear transfer, and genetic modification of germline cells, tools that are enabled by artificial insemination and/or embryo transfer for implementation. I have been fortunate in being able to contribute to the development of many of the above techniques, and to use them for research and applications for improving animal agriculture. Others have built on this work to circumvent human infertility, assist reproduction of companion animals, and rescue endangered species. It also has been a privilege to teach, mentor, and be mentored in this area. Resulting worldwide friendships have enriched me personally and professionally. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Environmentally Induced Epigenetic Transgenerational Inheritance and the Weismann Barrier: The Dawn of Neo-Lamarckian Theory

For the past 120 years, the Weismann barrier and associated germ plasm theory of heredity have been a doctrine that has impacted evolutionary biology and our concepts of inheritance through the germline. Although August Weismann in his 1872 book was correct that the sperm and egg were the only cells to transmit molecular information to the subsequent generation, the concept that somatic cells do not impact the germline (i.e., the Weismann barrier) is incorrect. However, the doctrine or dogma of the Weismann barrier still influences many scientific fields and topics. The discovery of epigenetics, and more recently environmentally induced epigenetic transgenerational inheritance of phenotypic variation and pathology, have had significant impacts on evolution theory and medicine today. Environmental epigenetics and the concept of epigenetic transgenerational inheritance refute aspects of the Weismann barrier and require a re-evaluation of both inheritance theory and evolution theory.

Wharton's jelly derived mesenchymal stem cells differentiate into oocyte like cells in vitro by follicular fluid and cumulus cells conditioned medium

Wharton's jelly derived-mesenchymal stem cells (WJ-MSCs) have a same developmental origin with primordial germ cells. WJ-MSCs perhaps differentiate into oocyte and germ like-cells (OLCs/GLCs) in the presence of appropriate inducers. Human follicular fluid (FF) and cumulus cells conditioned medium (CCM) are naturally rich sources for oocyte development. The aim of this study was to evaluate WJ-MSCs potential for differentiating into OLCs and GLCs exposed to FF and CCM. WJ-MSCs were cultured in two different induction media (10% FF, 10% CCM) for 21 days. Morphological changes and expression of developmental genes were evaluated on days 0, 7, 14 and 21 of culture. Also, on 21^st day of culture, the expression of oocyte and germ cell proteins investigated using immunofluorescence staining. Appearance of round shaped cells from 7^th day onwards indicated that WJ-MSCs can differentiate into OLCs when exposed to FF and CCM. The size of produced OLCs and expression of oocyte specific genes and proteins were increased more positively in FF group rather than CCM group. Although, WJ-MSCs could differentiate into OLCs by FF and CCM, however, the induction potential of FF for producing OLCs was better than CCM.

Breakthroughs and new horizons in reproductive biology of rare and endangered animal species

Because of higher extinction rates due to human and natural factors, more basic and applied research in reproductive biology is required to preserve wild species and design proper strategies leading to sustainable populations. The objective of the review is to highlight recent, inspiring breakthroughs in wildlife reproduction science that will set directions for future research and lead to more successes in conservation biology. Despite new tools and approaches allowing a better and faster understanding of key mechanisms, we still know little about reproduction in endangered species. Recently, the most striking advances have been obtained in nonmammalian species (fish, birds, amphibians, or corals) with the development of alternative solutions to preserve fertility or new information about parental nutritional influence on embryo development. A novel way has also been explored to consider the impact of environmental changes on reproduction-the allostatic load-in a vast array of species (from primates to fish). On the horizon, genomic tools are expected to considerably change the way we study wildlife reproduction and develop a concept of "precision conservation breeding." When basic studies in organismal physiology are conducted in parallel, new approaches using stem cells to create artificial gametes and gonads, innovations in germplasm storage, and more research on reproductive microbiomes will help to make a difference. Lastly, multiple challenges (for instance, poor integration of new tools in conservation programs, limited access to study animals, or few publication options) will have to be addressed if we want reproductive biology to positively impact conservation of biodiversity.

Necessity is the mother of invention and the evolutionary force driving the success of in vitro fertilization

During the last few decades, millions of healthy children have been born with the aid of in vitro fertilization (IVF). This success belies the fact that IVF treatment is comprised of a complex series of interventions starting with a customized control ovarian stimulation protocol. This is followed by the induction of oocyte maturation, the retrieval of mature oocytes and in vitro fertilization, which often involves the microinjection of a single sperm into the oocyte. After fertilization, the resulting embryos are cultured for up to 7 days. The best embryos are transferred into the uterus where the embryo implants and hopefully develops into a healthy child. However, frequently the best embryos are biopsied and frozen. The biopsied cells are analyzed to identify those embryos without chromosomal abnormalities. These embryos are eventually thawed and transferred with pregnancy rates as good if not better than embryos that are not biopsied and transferred in a fresh cycle. Thus, IVF treatment requires the coordinated efforts of physicians, nurses, molecular biologists and embryologists to conduct each of these multifaceted phases in a seamless and flawless manner. Even though complex, IVF treatment may seem routine today, but it was not always the case. In this review the evolution of human IVF is presented as a series of innovations that resolved a technical hurdle in one component of IVF while creating challenges that eventually lead to the next major advancement. This step-by-step evolution in the treatment of human infertility is recounted in this review.

Derivation and propagation of spermatogonial stem cells from human pluripotent cells

OBJECTIVES

This study is designed to generate and propagate human spermatogonial stem cells (SSCs) derived from human pluripotent stem cells (hPSCs).

METHODS

hPSCs were differentiated into SSC-like cells (SSCLCs) by a three-step strategy. The biological characteristics of SSCLCs were detected by immunostaining with antibodies against SSC markers. The ability of self-renewal was measured by propagating for a long time and still maintaining SSCs morphological property. The differentiation potential of SSCLCs was determined by the generation of spermatocytes and haploid cells, which were identified by immunostaining and flow cytometry. The transcriptome analysis of SSCLCs was performed by RNA sequencing. The biological function of SSCLCs was assessed by xeno-transplantation into busulfan-treated mouse testes.

RESULTS

SSCLCs were efficiently generated by a 3-step strategy. The SSCLCs displayed a grape-like morphology and expressed SSC markers. Moreover, SSCLCs could be propagated for approximately 4 months and still maintained their morphological properties. Furthermore, SSCLCs could differentiate into spermatocytes and haploid cells. In addition, SSCLCs displayed a similar gene expression pattern as human GPR125⁺ spermatogonia derived from human testicular tissues. And more, SSCLCs could survive and home at the base membrane of seminiferous tubules.

CONCLUSION

SSCLCs were successfully derived from hPSCs and propagated for a long time. The SSCLCs resembled their counterpart human GPR125⁺ spermatogonia, as evidenced by the grape-like morphology, transcriptome, homing, and functional characteristics. Therefore, hPSC-derived SSCLCs may provide a reliable cell source for studying human SSCs biological properties, disease modeling, and drug toxicity screening.

[George Lucas: prophet of transhumanism?]

Star Wars, a "general public" film saga, raises questions about human nature and transhumanism. It features different characters who are neither "real" humans nor robots; there are creatures that can be likened to advanced humans (cyborgs, chimeras or genetically-modified humans). Based on the "Star Wars" movie, we will approach some ways of modifying the human person both in his body and in his consciousness and we will wonder about the man of tomorrow by asking ourselves if George Lucas (director of the first film released) might have not been a visionary of the men of tomorrow.

In Vitro Generation of Oocyte Like Cells and Their In Vivo Efficacy: How Far We have been Succeeded

In the last few decades, stem cell therapy has grown as a boon for many pathological complications including female reproductive disorders. In this review, a brief description of available strategies that are related to stem cell-based in vitro oocyte-like cell (OLC) development are given. We have tried to cover all the aspects and latest updates of the in vitro OLC developmental methodologies, marker profiling, available disease models, and in vivo efficacies, with a special focus on mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs), and embryonic stem cells (ESCs) usage. The differentiation abilities of both the ovarian and non-ovarian stem cell sources under various induction conditions have shown different effects on morphological alterations, proliferation- and size-associated developments, hormonal secretions under gonadotropic stimulations, and their neo-oogenesis or folliculogenesis abilities after in vivo transplantations. The attainment of characters like oocyte-like morphology, size expansion, and meiosis initiation have been found to be major obstacles during in vitro oogenesis. A number of reports have either lacked in vivo studies or have shown their functional incapability to produce viable and healthy offspring. Though researchers have gained many valuable insights regarding in vitro gametogenesis, still there are many things to do to make stem cell-derived OLCs fully functional.

Fertility Preservation in Women With Malignancy: Future Endeavors

The area of fertility preservation is constantly developing. To date, the only noninvestigational and unequivocally accepted methods for fertility preservation are cryopreservation of embryos and unfertilized oocytes. This article is one of several in a monogram on fertility preservation. The debate, pros and cons, and equivocal data on the use of GnRH analogues for fertility preservation are elaborated by 3 other manuscripts, in this monogram. A repeat of the arguments, pros and cons of this debatable issue, would be a repetition and redundancy of what is already included in this monogram. The subject of ovarian cryopreservation for fertility preservation is also elaborated by several other authors in this monogram. It is possible that, in the not too far future, the technologies of in vitro maturation of primordial follicles to metaphase 2 oocytes, and the “artificial ovary,” will turn clinically available. These technologies may bypass the risk of resuming malignancy by autotransplantation of cryopreserved-thawed ovarian tissue in leukemia and diseases where malignant cells may persist in the cryopreserved ovarian tissue. We summarize here the suggested options for future endeavors in fertility preservation.

Fertility preservation in patients with hematologic malignancies and recipients of hematopoietic cell transplants

Patients with hematologic malignancies and those undergoing hematopoietic cell transplantation (HCT) face a complex set of challenges when considering options for fertility preservation (FP). There are no standard options for prepubertal children, and women with hematologic malignancies may not be eligible for standard FP options. Fortunately, initial therapies for most blood cancers are not highly gonadotoxic, affording an important opportunity for postremission counseling and referrals to fertility specialists. These patients face a high risk of relapse, and many will be referred for autologous or allogeneic HCT, which carries an extremely high risk of infertility. The expanding indications for HCT to include benign hematologic disorders as well as autoimmune diseases mandate that all hematologists are familiar with these risks. Oncofertility researchers are continually pushing the boundaries of what may be possible for our patients; in the meantime, communication and shared decision-making between hematologists and patients, as well as program-building, education, and outreach are essential to ensure that these patients, many of whom will be cured, maintain all of their options for a fulfilling life after intensive therapy.

Autologous activated platelet-rich plasma injection into adult human ovary tissue: molecular mechanism, analysis, and discussion of reproductive response

In clinical infertility practice, one intractable problem is low (or absent) ovarian reserve which in turn reflects the natural oocyte depletion associated with advancing maternal age. The number of available eggs has been generally thought to be finite and strictly limited, an entrenched and largely unchallenged tenet dating back more than 50 years. In the past decade, it has been suggested that renewable ovarian germline stem cells (GSCs) exist in adults, and that such cells may be utilized as an oocyte source for women seeking to extend fertility. Currently, the issue of whether mammalian females possess such a population of renewable GSCs remains unsettled. The topic is complex and even agreement on a definitive approach to verify the process of 'ovarian rescue' or 're-potentiation' has been elusive. Similarities have been noted between wound healing and ovarian tissue repair following capsule rupture at ovulation. In addition, molecular signaling events which might be necessary to reverse the effects of reproductive ageing seem congruent with changes occurring in tissue injury responses elsewhere. Recently, clinical experience with such a technique based on autologous activated platelet-rich plasma (PRP) treatment of the adult human ovary has been reported. This review summarizes the present state of understanding of the interaction of platelet-derived growth factors with adult ovarian tissue, and the outcome of human reproductive potential following PRP treatment.

Female Age Affects the Mesenchymal Stem Cell Characteristics of Aspirated Follicular Cells in the In Vitro Fertilization Programme

Aspirated follicular cells (AFCs) from the in vitro fertilization program can express various stem cell markers and are even able to differentiate into different types of cells in vitro. The female reproductive potential decreases with increasing age due to lowered ovarian reserve and oocyte quality, but data on the effect of female age on stem cell characteristics of AFCs are scarce. Therefore, the aim of this study was to elucidate whether female age affects the mesenchymal stem cell (MSC) characteristics of AFCs. Follicular aspirates were collected from 12 patients included in the in vitro fertilization programme with a normal ovarian reserve. Patients were divided into four age groups: Group A ≤ 30 years, Group B 31-35 years, Group C 36-39 years and Group D ≥ 40 years. After removal of the oocytes, AFCs were collected from follicular aspirates using hypo-osmotic technique and cultured in vitro, and their stemness was compared according to female age. The cultured AFCs were analysed for gene expression using the Human Mesenchymal Stem Cell RT² Profiler™ PCR Array, for their potential for differentiation into adipogenic and osteogenic lineage, and for their expression of MSC-related markers using immunocytochemistry. We found that female age can significantly influence their stemness: expression of pluripotency and MSC-related genes, and their differentiation potential. Despite the relatively high expression of MSC-related genes, the AFCs of the oldest patients had the lowest potential to differentiate into osteogenic and adipogenic lineages in vitro, which may be related to their age and the changed ovarian function.

Stem cells survive oncotherapy & can regenerate non-functional gonads: A paradigm shift for oncofertility

A large proportion of patients who survive cancer are rendered infertile as an unwanted side effect of oncotherapy. Currently accepted approaches for fertility preservation involve banking eggs/sperm/embryos or ovarian/testicular tissue before oncotherapy for future use. Such approaches are invasive, expensive, technically challenging and depend on assisted reproductive technologies (ART). Establishing a gonadal tissue bank (for cancer patients) is also fraught with ethical, legal and safety issues. Most importantly, patients who find it difficult to meet expenses towards cancer treatment will find it difficult to meet expenses towards gonadal tissue banking and ART to achieve parenthood later on. In this review an alternative strategy to regenerate non-functional gonads in cancer survivors by targeting endogenous stem cells that survive oncotherapy is discussed. A novel population of pluripotent stem cells termed very small embryonic-like stem cells (VSELs), developmentally equivalent to late migratory primordial germ cells, exists in adult gonads and survives oncotherapy due to their quiescent nature. However, the stem-cell niche gets compromised by oncotherapy. Transplanting niche cells (Sertoli or mesenchymal cells) can regenerate the non-functional gonads. This approach is safe, has resulted in the birth of fertile offspring in mice and could restore gonadal function early in life to support proper growth and later serve as a source of gametes. This newly emerging understanding on stem cells biology can obviate the need to bank gonadal tissue and fertility may also be restored in existing cancer survivors who were earlier deprived of gonadal tissue banking before oncotherapy.

Carry on editing

INTRODUCTION OR BACKGROUND

Genome editing facilitates alterations to DNA, large or subtle, in a precise fashion. In its most popular form it uses the programmable endonuclease system, CRISPR/Cas9. Edits can be made to any genome, including the human genome. This raises the possibility of genome editing in human embryos in both a research and reproductive context.

SOURCES OF DATA

All reports of genome editing in human embryos are included here, along with key papers examining the science and ethics of human genome editing.

AREAS OF AGREEMENT

As a basic research tool, genome editing promises to accelerate our understanding of genome biology. It also shows great promise as a means of combatting disease through so-called somatic genome editing.

AREAS OF CONTROVERSY

Genome editing could be used to prevent human disease transmission in a reproductive context. Such germ line interventions are opposed by some, for a number of reasons. Some of these reasons are discussed and a comparison is made with preimplantation genetic diagnosis (PGD).

GROWING POINTS

It is important that scientists, clinicians, bioethicists and other stakeholders engage widely with all those with an interest in genome editing.

AREAS TIMELY FOR DEVELOPING RESEARCH

In addition to offering new insights into human biology, basic (fundamental) research will deliver expertise allowing ever more precise and controllable genome editing methodologies and allied technologies. A range of clear and accessible ethical frameworks must be developed and scrutinized as part of a wider societal debate about possible applications of genome editing. In the UK, human reproductive genome editing can only take place if a change to primary legislation occurs. Inclusive discussions and assessments, involving difficult scientific and ethical concepts, must form part of any democratic decision.

Oocytes from stem cells

Folliculogenesis describes the process of activating an oocyte-containing primordial follicle from the ovarian reserve and its development to the mature ovulatory stage. This process is highly complex and is controlled by extra- and intra-ovarian signaling events. Oocyte competence and capacity for fertilization to support a viable pregnancy are acquired during folliculogenesis. Cancer and cancer-based therapies can negatively affect this process, compromising fertility. Currently, preservation of fertility in these patients remains limited to surrogacy, oocyte freezing, oocyte donation, or in vitro maturation (IVM). Recent reports of stem cells being used to produce fully competent oocytes and subsequently healthy offspring in mice have opened up a novel avenue for fertility preservation. However, translating these findings into human health first relies on enhancing our understanding of follicle growth and mimicking its intricacies in vitro. Indeed, the future of oocytes from stem cells in humans comes with many possibilities but currently faces several technical and ethical obstacles.

Ovarian stem cells-resolving controversies

A recent review on ovarian stem cells by Horan and Williams entitled "Oocyte Stem Cells: Fact or Fantasy?" suggests that the debate on ovarian stem cells (OSCs) is still not over. They did not even discuss the presence of two distinct populations of stem cells in the ovary in their review. OSCs are located in the ovary surface epithelium and Tilly's group reported them in the size range of 5-8 μm whereas Virant-Klun's group has reported pluripotent, 2-4 μm OSCs. Our group reported OSCs of two distinct sizes including pluripotent very small embryonic-like stem cells (VSELs) which are smaller in size than RBCs (similar to those reported by Virant-Klun's group) and slightly bigger (similar to those reported by Tilly's group) tissue committed progenitors (OSCs) that presumably differentiate from VSELs. These stem/progenitor cells express receptors for follicle stimulating hormone (FSH) and are activated by FSH. Our opinion article provides explanation to several open-ended questions raised in the review on OSCs by Horan and Williams. VSELs survive chemotherapy; maintain life-long homeostasis; loss of their function due to a compromised niche results in age-related senescence and presence of overlapping pluripotent markers suggest that they may also be implicated in epithelial ovarian cancers.