Transplantation directs oocyte maturation from embryonic stem cells and provides a therapeutic strategy for female infertility

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.

Synergistic effect of Huyang Yangkun Formula and embryonic stem cells on 4-vinylcyclohexene diepoxide induced premature ovarian insufficiency in mice

Background

Huyang Yangkun Formula (HYYKF) was developed based on theory of traditional Chinese medicine as well as clinical experience and used to improve ovarian function of premature ovarian insufficiency (POI) patients. Transplantation of embryonic stem cells (ESCs) has great potential in improving POI, and studies have confirmed that traditional Chinese medicine promoted the treatment effect of ESCs. In the present study, we compared the effect of combining HYYKF and ESCs, single HYYKF treatment and single ESCs intervention on POI mice to explore the effect of combination of HYYKF and ESCs in improving ovarian function.

Methods

C57BL/6 mice were used to create a POI model by 15-day intraperitoneal injection of 160 mg/kg of 4-vinylcyclonhexene diepoxide (VCD) and then treated with HYYKF, ESCs transplantation and combination of ESCs and HYYKF. When the treatments were finished, estrus cycle, ovarian follicle counting, serum sex hormone level, and expression of key nodes in the transforming growth factor beta/transforming growth factor beta-activated kinase 1 (TGF-β/TAK1) signaling pathway were determined.

Results

Combination therapy brought down the abnormal estrus cycle rate to 5.26%, significantly lower than that of HYYKF or ESCs alone (30%, 25%, respectively). The numbers of follicles at all levels were increased significantly in the combination ESCs with HYYKF group (P < 0.05), especially that of antral follicles (P < 0.01), which was not increased significantly when HYYKF or ESCs was single used. The level of anti-Mullerian hormone (AMH) was more significantly increased in the combination ESCs with HYYKF group (P < 0.01) than that of HYYKF or ESCs alone (both P < 0.05). The expression of the key nodes TGF-β1, TAK1, JNK, Smad4 and FSHR in the TGF-β/TAK1 pathway were obviously affected in the SCHY group.

Conclusion

Both HYYKF and ESCs improve the ovarian function of POI induced by VCD, and a combination of HYYKF and ESCs has the advantage that they work together to promote follicles developing probably by inhibiting expression of the TGF-β1/TAK1 pathway.

Derivation of oocyte-like cells from putative embryonic stem cells and parthenogenetically activated into blastocysts in goat

Germ cells are responsible for the propagation of live animals from generation to generation, but to surprise, a steep increase in infertile problems among livestock poses great threat for economic development of human race. An alternative and robust approach is essential to combat these ailments. Here, we demonstrate that goat putative embryonic stem cells (ESCs) were successfully in vitro differentiated into primordial germ cells and oocyte-like cells using bone morphogenetic protein-4 (BMP-4) and trans-retinoic acid (RA). Oocyte-like cells having distinct zonapellucida recruited adjacent somatic cells in differentiating culture to form cumulus-oocyte complexes (COCs). The putative COCs were found to express the zonapellucida specific (ZP1 and ZP2) and oocyte-specific markers. Primordial germ cell-specific markers VASA, DAZL, STELLA, and PUM1 were detected at protein and mRNA level. In addition to that, the surface architecture of these putative COCs was thoroughly visualized by the scanning electron microscope. The putative COCs were further parthenogenetically activated to develop into healthy morula, blastocysts and hatched blastocyst stage like embryos. Our findings may contribute to the fundamental understanding of mammalian germ cell biology and may provide clinical insights regarding infertility ailments.

Female Fertility Preservation through Stem Cell-based Ovarian Tissue Reconstitution In Vitro and Ovarian Regeneration In Vivo

Historically, approaches designed to offer women diagnosed with cancer the prospects of having a genetically matched child after completion of their cytotoxic treatments focused on the existing oocyte population as the sole resource available for clinical management of infertility. In this regard, elective oocyte and embryo cryopreservation, as well as autologous ovarian cortical tissue grafting posttreatment, have gained widespread support as options for young girls and reproductive-age women who are faced with cancer to consider. In addition, the use of ovarian protective therapies, including gonadotropin-releasing hormone agonists and sphingosine-1-phosphate analogs, has been put forth as an alternative way to preserve fertility by shielding existing oocytes in the ovaries in vivo from the side-effect damage caused by radiotherapy and many chemotherapeutic regimens. This viewpoint changed with the publication of now numerous reports that adult ovaries of many mammalian species, including humans, contain a rare population of oocyte-producing germ cells-referred to as female germline or oogonial stem cells (OSCs). This new line of study has fueled research into the prospects of generating new oocytes, rather than working with existing oocytes, as a novel approach to sustain or restore fertility in female cancer survivors. Here, we overview the history of work from laboratories around the world focused on improving our understanding of the biology of OSCs and how these cells may be used to reconstitute "artificial" ovarian tissue in vitro or to regenerate damaged ovarian tissue in vivo as future fertility-preservation options.

[In vitro oogenesis: How far have we come?]

Oogenesis is a complex cellular and molecular process whose fundamental mechanisms are still poorly described or not yet elucidated, especially in human species. The development of an in vitro model of oogenesis, particularly during fetal development in humans, is a critical step that would allow: (i) a better understand of the biological mechanisms of oogenesis; (ii) a refinement of medical diagnosis for women suffering from infertility; and (iii) providing new therapeutics for reproductive pathologies. The genesis of this model could be considered from ES/iPS cells. In this article, we will trace the physiological mechanisms of oogenesis in vivo and discuss the studies carried out in the field of in vitro oogenesis from ES/iPS cells, as well as the challenges to be met in the future.

Complete in vitro oogenesis: retrospects and prospects

Precise control of mammalian oogenesis has been a traditional focus of reproductive and developmental biology research. Recently, new reports have introduced the possibility of obtaining functional gametes derived in vitro from stem cells. The potential to produce functional gametes from stem cells has exciting applications for regenerative medicine though still remains challenging. In mammalian females ovulation and fertilization is a privilege reserved for a small number of oocytes. In reality the vast majority of oocytes formed from primordial germ cells (PGCs) will undergo apoptosis, or other forms of cell death. Removal occurs during germ cell cyst breakdown and the establishment of the primordial follicle (PF) pool, during the long dormancy at the PF stage, or through follicular atresia prior to reaching the ovulatory stage. A way to solve this limitation could be to produce large numbers of oocytes, in vitro, from stem cells. However, to recapitulate mammalian oogenesis and produce fertilizable oocytes in vitro is a complex process involving several different cell types, precise follicular cell-oocyte reciprocal interactions, a variety of nutrients and combinations of cytokines, and precise growth factors and hormones depending on the developmental stage. In 2016, two papers published by Morohaku et al. and Hikabe et al. reported in vitro procedures that appear to reproduce efficiently these conditions allowing for the production, completely in a dish, of a relatively large number of oocytes that are fertilizable and capable of giving rise to viable offspring in the mouse. The present article offers a critical overview of these results as well as other previous work performed mainly in mouse attempting to reproduce oogenesis completely in vitro and considers some perspectives for the potential to adapt the methods to produce functional human oocytes.

Ovarian regeneration: The potential for stem cell contribution in the postnatal ovary to sustained endocrine function

The endocrine function of the ovary is dependent upon the ovarian follicle, which on a cellular basis consists of an oocyte surrounded by adjacent somatic cells responsible for generating sex steroid hormones and maintenance of hormonal stasis with the hypothalamic-pituitary axis. As females age, both fertility and the endocrine function of the ovary decline due to waning follicle numbers as well as aging-related cellular dysfunction. Although there is currently no cure for ovarian failure and endocrine disruption, recent advances in ovarian biology centered on ovarian stem cell and progenitor cell populations have brought the prospects of cell- or tissue-based therapeutic strategies closer to fruition. Herein, we review the relative contributions of ovarian stem cells to ovarian function during the reproductive lifespan, and postulate steps toward the development of ovarian stem cell-based approaches to advance fertility treatments, and also importantly to provide a physiological long-term means of endocrine support.

In Vitro Gamete Differentiation from Pluripotent Stem Cells as a Promising Therapy for Infertility

Generation of gametes derived in vitro from pluripotent stem cells holds promising prospects for future reproductive applications. Indeed, it provides information on molecular and cellular mechanisms underlying germ cell (GC) development and could offer a new potential treatment for infertility. Great progress has been made in derivation of gametes from embryonic stem cells, despite ethical issues. Induced pluripotent stem cells (iPSCs) technology allows the reprogramming of a differentiated somatic cell, possibly emanating from the patient, into a pluripotent state. With the emergence of iPSCs, several studies created primordial GC stage to mature gamete-like cells in vitro in mice and humans. Recent findings in GC derivation suggest that in mice, functional gametes can be generated in vitro. This strengthens the idea that it might be possible in the future to generate functional human sperm and oocytes from pluripotent stem cells in culture.

Differentiation of human menstrual blood-derived endometrial mesenchymal stem cells into oocyte-like cells

Human endometrial mesenchymal stem cells (EnSCs) derived from menstrual blood are a unique stem cell source. Evidence suggests that EnSCs exhibit a multi-lineage potential and have attracted extensive attention in regenerative medicine. However, the potential of EnSCs to differentiate into germline cells in vitro remains unclear. In this study, EnSCs were induced to differentiate into germ cells in a differentiation medium supplemented with 20% human follicular fluid. Our results demonstrated that EnSCs derived from human menstrual blood form oocyte-like cells and express germ cell markers. The induced cell aggregates contained not only oocyte-like structures but also cells expressing follicle stimulating hormone receptor and luteotropic hormone receptor, and produced estrogen and progesterone regulated by gonodatropin, suggesting that granulosa-like and theca-like cells were also induced. We further found that granulosa cells promote the development of oocyte-like cells and activate the induction of blastocyst-like structures derived from EnSCs. In conclusion, EnSCs may potentially represent an in vitro system for the investigation of human folliculogenesis.

A gonogenic stimulated transition of mouse embryonic stem cells with enhanced control of diverse differentiation pathways

Embryonic stem (ES) cells share markers with undifferentiated primordial germ cells (PGCs). Here, we discovered that a cellular state with some molecular markers of male gonocyte induction, including a G1/S phase arrest and upregulation of specific genes such as Nanos2, Tdrd1, Ddx4, Zbtb16 and Plk1s1, can be chemically induced in male mouse ES cells in vitro, which we termed gonogenic stimulated transition (GoST). After longer culture of the resulting GoST cells without chemical stimulation, several molecular markers typical for early gonocytes were detected including the early gonocyte marker Tex101. Motivated by previous studies that found multipotency in cell lines derived from neonatal male germ cells in vitro, we then compared the differentiation potential of GoST cells to that of ES cells in vitro. Interestingly, GoST cells showed equal neurogenic, but enhanced cardiogenic and hepatogenic differentiation compared to ES cells in vitro. This work shows for the first time that some important molecular markers of the first developmental sexual differentiation program can be induced in male mouse ES cells in vitro and defines a novel concept to generate cells with enhanced multipotency.

In vitro differentiation of germ cells from stem cells: a comparison between primordial germ cells and in vitro derived primordial germ cell-like cells

Stem cells are unique cell types capable to proliferate, some of them indefinitely, while maintaining the ability to differentiate into a few or any cell lineages. In 2003, a group headed by Hans R. Schöler reported that oocyte-like cells could be produced from mouse embryonic stem (ES) cells in vitro. After more than 10 years, where have these researches reached? Which are the major successes achieved and the problems still remaining to be solved? Although during the last years, many reviews have been published about these topics, in the present work, we will focus on an aspect that has been little considered so far, namely a strict comparison between the in vitro and in vivo developmental capabilities of the primordial germ cells (PGCs) isolated from the embryo and the PGC-like cells (PGC-LCs) produced in vitro from different types of stem cells in the mouse, the species in which most investigation has been carried out. Actually, the formation and differentiation of PGCs are crucial for both male and female gametogenesis, and the faithful production of PGCs in vitro represents the basis for obtaining functional germ cells.

Artificial gametes from stem cells

The generation of artificial gametes is a real challenge for the scientific community today. In vitro development of human eggs and sperm will pave the way for the understanding of the complex process of human gametogenesis and will provide with human gametes for the study of infertility and the onset of some inherited disorders. However, the great promise of artificial gametes resides in their future application on reproductive treatments for all these people wishing to have genetically related children and for which gamete donation is now their unique option of parenthood. This is the case of infertile patients devoid of suitable gametes, same sex couples, singles and those fertile couples in a high risk of transmitting serious diseases to their progeny. In the search of the best method to obtain artificial gametes, many researchers have successfully obtained human germ cell-like cells from stem cells at different stages of differentiation. In the near future, this field will evolve to new methods providing not only viable but also functional and safe artificial germ cells. These artificial sperm and eggs should be able to recapitulate all the genetic and epigenetic processes needed for the correct gametogenesis, fertilization and embryogenesis leading to the birth of a healthy and fertile newborn.

Effect of BMP4 preceded by retinoic acid and co-culturing ovarian somatic cells on differentiation of mouse embryonic stem cells into oocyte-like cells

Bone morphogenetic protein 4 (BMP4) and retinoic acid (RA) signaling are the key regulators for germ cell and meiosis induction, respectively. Gonadal tissue also provides an appropriate microenvironment for oocyte differentiation in vivo. The current study aimed to determine whether mimicking in vivo niche is more efficient for oocyte differentiation from embryonic stem (ES) cells. Here, differentiation of mouse ES cells toward oocyte-like cells using embryoid body (EB) and monolayer protocols was induced in the presence (+BMP4) or absence (-BMP4) of BMP4. On day 5, each group was co-cultured with ovarian somatic cells in the presence or absence of RA (+RA or -RA) for an additional 14 days. Our results showed a significant increase in expression of meiotic markers in the +BMP4 condition in EB differentiation protocol. Further differentiation with ovarian somatic cells led to a subpopulation of oocyte-like cell formation. Compared to the controls, the +RA condition resulted in a significant elevation of the meiotic gene expression in contrast to Oct4 that significantly decreased in both protocols. In the cells pre-treated with BMP4 and then exposed to RA in the monolayer differentiation protocol, the gene expression levels of germ cell, Mvh, and maturation markers, Cx37, Zp2, and Gdf9, were also upregulated significantly. Therefore, it can be concluded that +BMP4 and +RA along with ovarian somatic cell co-culture improved the rate of in vitro oocyte differentiation.

Postnatal oogenesis in humans: a review of recent findings

In spite of generally accepted dogma that the total number of follicles and oocytes is established in human ovaries during the fetal period of life rather than forming de novo in adult ovaries, some new evidence in the field challenges this understanding. Several studies have shown that different populations of stem cells, such as germinal stem cells and small round stem cells with diameters of 2 to 4 μm, that resembled very small embryonic-like stem cells and expressed several genes related to primordial germ cells, pluripotency, and germinal lineage are present in adult human ovaries and originate in ovarian surface epithelium. These small stem cells were pushed into the germinal direction of development and formed primitive oocyte-like cells in vitro. Moreover, oocyte-like cells were also formed in vitro from embryonic stem cells and induced pluripotent stem cells. This indicates that postnatal oogenesis is not excluded. It is further supported by the occurrence of mesenchymal stem cells that can restore the function of sterilized ovaries and lead to the formation of new follicles and oocytes in animal models. Both oogenesis in vitro and transplantation of stem cell-derived "oocytes" into the ovarian niche to direct their natural maturation represent a big challenge for reproductive biomedicine in the treatment of female infertility in the future and needs to be explored and interpreted with caution, but it is still very important for clinical practice in the field of reproductive medicine.

Emerging methods to generate artificial germ cells from stem cells

Germ cells are responsible for the transmission of genetic and epigenetic information across generations. At present, the number of infertile couples is increasing worldwide; these infertility problems can be traced to environmental pollutions, infectious diseases, cancer, psychological or work-related stress, and other factors, such as lifestyle and genetics. Notably, lack of germ cells and germ cell loss present real obstacles in infertility treatment. Recent research aimed at producing gametes through artificial germ cell generation from stem cells may offer great hope for affected couples to treat infertility in the future. Therefore, this rapidly emerging area of artificial germ cell generation from nongermline cells has gained considerable attention from basic and clinical research in the fields of stem cell biology, developmental biology, and reproductive biology. Here, we review the state of the art in artificial germ cell generation.

Cell therapy for chemically induced ovarian failure in mice

Cell therapy has been linked to an unexplained return of ovarian function and fertility in some cancer survivors. Studies modeling this in mice have shown that cells transplantation generates donor-derived oocytes in chemotherapy-treated recipients. This study was conducted to further clarify the impact of cell transplantation from different sources on female reproductive function after chemotherapy using a preclinical mouse model. Methods. Female mice were administered 7.5 mg/kg cisplatin followed by cell transplantation (one week later) using GFP+ female cell donors. For cell tracking, adipose derived stem cell GFP+ (ADSC), female germline stem cell GFP+/MVH+ (FGSC), or ovary cell suspension GFP+ mice were transplanted into cisplatin-treated wild-type recipients. After 7 or 14 days animals were killed and histological analysis, IHQ for GFP cells, and ELISA for estradiol were performed. Results. Histological examinations showed that ADSC, ovary cell suspension, and FGSC transplant increase the number of follicles with apparent normal structure in the cells recipient group euthanized on day 7. Cell tracking showed GFP+ samples 7 days after transplant. Conclusion. These data suggest that intraovarian injection of ADSCs and FGSC into mice with chemotherapy-induced ovarian failure diminished the damage caused by cisplatin.

Human iPS Cell-Derived Germ Cells: Current Status and Clinical Potential

Recently, fertile spermatozoa and oocytes were generated from mouse induced pluripotent (iPS) cells using a combined in vitro and in vivo induction system. With regard to germ cell induction from human iPS cells, progress has been made particularly in the male germline, demonstrating in vitro generation of haploid, round spermatids. Although iPS-derived germ cells are expected to be developed to yield a form of assisted reproductive technology (ART) that can address unmet reproductive needs, genetic and/or epigenetic instabilities abound in iPS cell generation and germ cell induction. In addition, there is still room to improve the induction protocol in the female germline. However, rapid advances in stem cell research are likely to make such obstacles surmountable, potentially translating induced germ cells into the clinical setting in the immediate future. This review examines the current status of the induction of germ cells from human iPS cells and discusses the clinical potential, as well as future directions.

Human germ cell formation in xenotransplants of induced pluripotent stem cells carrying X chromosome aneuploidies

Turner syndrome is caused by complete or partial loss of the second sex chromosome and is characterized by spontaneous fetal loss in >90% of conceptions. Survivors possess an array of somatic and germline clinical characteristics. Induced pluripotent stem cells (iPSCs) offer an opportunity for insight into genetic requirements of the X chromosome linked to Turner syndrome. We derived iPSCs from Turner syndrome and control individuals and examined germ cell development as a function of X chromosome composition. We demonstrate that two X chromosomes are not necessary for reprogramming or maintenance of pluripotency and that there are minimal differences in gene expression, at the single cell level, linked to X chromosome aneuploidies. Formation of germ cells, as assessed in vivo through a murine xenotransplantation model, indicated that undifferentiated iPSCs, independent of X chromosome composition, are capable of forming germ-cell-like cells (GCLCs) in vivo. In combination with clinical data regarding infertility in women with X chromosome aneuploidies, results suggest that two intact X chromosomes are not required for human germ cell formation, qualitatively or quantitatively, but rather are likely to be required for maintenance of human germ cells to adulthood.

Generation of mouse functional oocytes in rat by xeno-ectopic transplantation of primordial germ cells

Primordial germ cells (PGCs) are germ cell progenitors in the fetal genital ridge; female PGCs give rise to definitive oocytes that contribute to the next generation. Artificial PGCs have been induced in vitro from pluripotent stem cells and gonad-like tissue has been induced in vivo by cotransplantation of PGCs with PGC-free gonadal cells. To apply these technologies to human infertility treatment or conservation of rare species, PGC transplantation must be established in xenogenic animals. Here, we established a xenogeneic transplantation model by inducing ovary-like tissue from PGCs in xenogenic animals. We transplanted enzymatically dispersed PGCs with PGC-free gonadal cells under the kidney capsule of xenogenic immunodeficient animals. The transplanted cells formed ovary-like tissues under the kidney capsule. These tissues were histologically similar to the normal gonad and expressed the oocyte markers Vasa and Stella. In addition, mouse germinal vesicle-stage oocyte-like cells collected from ovary-like tissue in rats matured to metaphase II via in vitro maturation and gave rise to offspring by intracytoplasmic sperm injection. Our studies show that rat/mouse female PGCs and PGC-free gonadal cells can develop and reconstruct ovary-like tissue containing functional oocytes in an ectopic xenogenic microenvironment.

Fate of iPSCs derived from azoospermic and fertile men following xenotransplantation to murine seminiferous tubules

Historically, spontaneous deletions and insertions have provided means to probe germline developmental genetics in Drosophila, mouse and other species. Here, induced pluripotent stem cell (iPSC) lines were derived from infertile men with deletions that encompass three Y chromosome azoospermia factor (AZF) regions and are associated with production of few or no sperm but normal somatic development. AZF-deleted iPSC lines were compromised in germ cell development in vitro. Undifferentiated iPSCs transplanted directly into murine seminiferous tubules differentiated extensively to germ-cell-like cells (GCLCs) that localized near the basement membrane, demonstrated morphology indistinguishable from fetal germ cells, and expressed germ-cell-specific proteins diagnostic of primordial germ cells. Alternatively, all iPSCs that exited tubules formed primitive tumors. iPSCs with AZF deletions produced significantly fewer GCLCs in vivo with distinct defects in gene expression. Findings indicate that xenotransplantation of human iPSCs directs germ cell differentiation in a manner dependent on donor genetic status.

Induced pluripotent stem cell potential in medicine, specifically focused on reproductive medicine

Since 2006, several laboratories have proved that somatic cells can be reprogramed into induced pluripotent stem cells (iPSCs). iPSCs have enormous potential in stem cell biology as they can give rise to numerous cell lineages, including the three germ layers. In this review, we discuss past and recent advances in human iPSCs used for modeling diseases in vitro, screening drugs to test new treatments, and autologous cell and tissue regenerative therapies, with a special focus on reproductive medicine applications. While this latter field of research is still in its infancy, it holds great promise for investigating germ cell development and studying the genetic and physiopathological mechanisms of infertility. A major cause of infertility is the absence of germ cells in the testes, mainly due to genetic background or as a consequence of gonadotoxic treatments. For these patients, no effective fertility restoration strategy has so far been identified. The derivation of germ cells from iPSCs represents an alternative source of stem cells able to differentiate into spermatozoa. Lessons learned from animal models as well as studies on human iPSCs for reproductive purposes are reviewed.

The Mechanistic Links Between Proteasome Activity, Aging and Age-related Diseases

Damaged and misfolded proteins accumulate during the aging process, impairing cell function and tissue homeostasis. These perturbations to protein homeostasis (proteostasis) are hallmarks of age-related neurodegenerative disorders such as Alzheimer’s, Parkinson’s or Huntington’s disease. Damaged proteins are degraded by cellular clearance mechanisms such as the proteasome, a key component of the proteostasis network. Proteasome activity declines during aging, and proteasomal dysfunction is associated with late-onset disorders. Modulation of proteasome activity extends lifespan and protects organisms from symptoms associated with proteostasis disorders. Here we review the links between proteasome activity, aging and neurodegeneration. Additionally, strategies to modulate proteasome activity and delay the onset of diseases associated to proteasomal dysfunction are discussed herein.

Fate of induced pluripotent stem cells following transplantation to murine seminiferous tubules

Studies of human germ cell development are limited in large part by inaccessibility of germ cells during development. Moreover, although several studies have reported differentiation of mouse and human germ cells from pluripotent stem cells (PSCs) in vitro, differentiation of human germ cells from PSCs in vivo has not been reported. Here, we tested whether mRNA reprogramming in combination with xeno-transplantation may provide a viable system to probe the genetics of human germ cell development via use of induced pluripotent stem cells (iPSCs). For this purpose, we derived integration-free iPSCs via mRNA-based reprogramming with OCT3/4, SOX2, KLF4 and cMYC alone (OSKM) or in combination with the germ cell-specific mRNA, VASA (OSKMV). All iPSC lines met classic criteria of pluripotency. Moreover, global gene expression profiling did not distinguish large differences between undifferentiated OSKM and OSKMV iPSCs; however, some differences were observed in expression of pluripotency factors and germ cell-specific genes, and in epigenetic profiles and in vitro differentiation studies. In contrast, transplantation of undifferentiated iPSCs directly into the seminiferous tubules of germ cell-depleted immunodeficient mice revealed divergent fates of iPSCs produced with different factors. Transplantation resulted in morphologically and immunohistochemically recognizable germ cells in vivo, particularly in the case of OSKMV cells. Significantly, OSKMV cells also did not form tumors while OSKM cells that remained outside the seminiferous tubule proliferated extensively and formed tumors. Results indicate that mRNA reprogramming in combination with transplantation may contribute to tools for genetic analysis of human germ cell development.

Characterization of embryonic stem-like cells derived from HEK293T cells through miR302/367 expression and their potentiality to differentiate into germ-like cells

Human induced pluripotent stem (iPS) cells have great value for regenerative medicine, but are facing problems of low efficiency. MicroRNAs are a recently discovered class of 19-25 nt small RNAs that negatively target mRNAs. miR302/367 cluster has been demonstrated to reprogram mouse and human somatic cells to iPS cells without exogenous transcription factors, however, the repetition and differentiation potentiality of miR302/367-induced pluripotent stem (mirPS) cells need to be improved. Here, we showed overexpression of miR302/367 cluster reprogrammed human embryonic kidney 293T cells into mirPS cells in serum-free N2B27-based medium. The mirPS cells had similar morphology with embryonic stem cells, and expressed pluripotent markers including Oct4, Sox2, Klf4, and Nanog. In addition, through formation of embryoid bodies, various cells and tissues from three germ layers could be determined. Moreover, we examined the potential of mirPS cells differentiating into germ cells both in vitro and in vivo. Taken together, these data might provide a new source of cells and technique for the investigation of the mechanisms underlying reprogramming and pluripotency.

A comparison of the multiple oocyte maturation gene expression patterns between the newborn and adult mouse ovary

BACKGROUND

The interaction between follicular cells and oocyte leads to a change in gene expression involved in oocyte maturation processes.

OBJECTIVE

The purpose of this study was to quantify the expression of more common genes involved in follicular growth and oocyte developmental competence.

MATERIALS AND METHODS

In this experimental study, the expression of genes was evaluated with qRT-PCR assay in female BALB/c mice pups at 3-day of pre-pubertal and 8 week old virgin adult ovaries. The tissue was prepared by H&E staining for normal morphological appearance. The data were calculated with the 2-∆Ct formula and assessed using non-parametric two-tailed Mann-Whitney test. The p<0.05 was considered as significant.

RESULTS

The data showed a significant increase in the level of Stra8 and GDF9 in adult compared with newborn mice ovaries (p=0.049). In contrast, a significant decrease in the level of Mvh, REC8, SCP1, SCP3, and ZP2 was observed in adult mice ovaries compared to those in the newborn mice ovaries (all p=0.049 except SCP1: p=0.046). There was no significant difference in the level of OCT4 and Cx37 expression between adult and newborn mice ovaries.

CONCLUSION

The modifications in gene expression patterns coordinate the follicular developmental processes. Furthermore, the findings showed higher expression level of premeiotic gene (Stra8) and lower level of meiotic entry markers (SCP1, SCP3, and REC8) in juvenile than newborn mouse ovaries. This article extracted from Ph.D. thesis. (Nehleh Zarei fard).

Generation of germ cells in vitro in the era of induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are stem cells that can be artificially generated via "cellular reprogramming" using gene transduction in somatic cells. iPSCs have enormous potential in stem-cell biology as they can give rise to numerous cell lineages, including the three germ layers. An evaluation of germ-line competency by blastocyst injection or tetraploid complementation, however, is critical for determining the developmental potential of mouse iPSCs towards germ cells. Recent studies have demonstrated that primordial germ cells obtained by the in vitro differentiation of iPSCs produce functional gametes as well as healthy offspring. These findings illustrate not only that iPSCs are developmentally similar to embryonic stem cells (ESCs), but also that somatic cells from adult tissues can produce gametes in vitro, that is, if they are reprogrammed into iPSCs. In this review, we discuss past and recent advances in the in vitro differentiation of germ cells using pluripotent stem cells, with an emphasis on ESCs and iPSCs. While this field of research is still at a stage of infancy, it holds great promises for investigating the mechanisms of germ-cell development, especially in humans, and for advancing reproductive and developmental engineering technologies in the future.

Human amniotic fluid stem cells have a potential to recover ovarian function in mice with chemotherapy-induced sterility

BACKGROUND

Human amniotic fluid cells (hAFCs) may differentiate into multiple cell lineages and thus have a great potential to become a donor cell source for regenerative medicine. The ability of hAFCs to differentiate into germ cell and oocyte-like cells has been previously documented. Herein we report the potential use of hAFCs to help restore follicles in clinical condition involving premature ovarian failure.

RESULTS

Human amniotic fluid was obtained via amniocentesis, yielding a subpopulation of cloned hAFCs that was able to form embryoid bodies (EBs) and differentiate into three embryonic germ layers. Moreover, culture of EBs in medium containing human follicular fluid (HFF) or a germ cell maturation factor cocktail (FAC), expressed germ cells markers such as BLIMP1, STELLA, DAZL, VASA, STRA8, SCP3, SCP1, and GDF9. Furthermore, one cell line was grown from clone cells transfected with lentivirus-GFP and displaying morphological characteristics of mesenchymal cells, had the ability to restore ovarian morphology following cell injection into the ovaries of mice sterilized by intraperitoneal injection of cyclophosphamide and busulphan. Restored ovaries displayed many follicle-enclosed oocytes at all stages of development, but no oocytes or follicles were observed in sterilized mice whose ovaries had been injected with medium only (control). Notably, identification of GFP-labeled cells and immunostaining with anti-human antigen-specific antibodies demonstrated that grafted hAFCs survived and differentiated into granulosa cells which directed oocyte maturation. Furthermore, labeling of ovarian tissue for anti-Müllerian hormone expression, a functional marker of folliculogenesis, was strong in hAFCs-transplanted ovaries but inexistent in negative controls.

CONCLUSION

These findings highlight the possibility of using human amniotic fluid-derived stem cells in regenerative medicine, in particular in the area of reproductive health.

Location and characterization of female germline stem cells (FGSCs) in juvenile porcine ovary

OBJECTIVES

Existence of germline stem cells (GSCs) in juvenile mammalian female ovaries has been drastically debated recently since reports that adult mouse ovaries still have mitotically active germ cells have been proposed. In addition, definitive location of such female germline stem cells (FGSCs) had not been demonstrated.

MATERIALS AND METHODS

We segregated porcine FGSCs mechanically from ovary cortex, and tested our hypotheses by utilizing immunofluorescent staining, qRT-PCR and western blotting.

RESULTS

We attached emphasis to unambiguous location of FGSCs, which settle simultaneously in the theca. Dissected cells from porcine thecal layers maintained similar characteristics to mouse FGSCs and ESCs over 4-months in vitro culture.

CONCLUSION

These results may provide a new resource for the study of oogenesis and therapy for ovarian sterility.

Status of human germ cell differentiation from pluripotent stem cells

Historically, the quality of life of infertile couples has been greatly diminished by the loss of opportunity to conceive. However, beginning with the advent of IVF in the late 1970s, novel clinical interventions have greatly changed the outlook for those with severe forms of infertility. Yet, in cases in which the quality and quantity of germ cells are most compromised, there are few options. In the present paper, the current status of germ cell development from stem cells is reviewed in light of potential utility for basic science and clinical applications.

Oocyte differentiation is genetically dissociable from meiosis in mice

Oogenesis is the process by which ovarian germ cells undertake meiosis and differentiate to become eggs. In mice, Stra8 is required for the chromosomal events of meiosis to occur, but its role in differentiation remains unknown. Here we report Stra8-deficient ovarian germ cells that grow and differentiate into oocyte-like cells that synthesize zonae pellucidae, organize surrounding somatic cells into follicles, are ovulated in response to hormonal stimulation, undergo asymmetric cell division to produce a polar body and cleave to form two-cell embryos upon fertilization. These events occur without premeiotic chromosomal replication, sister chromatid cohesion, synapsis or recombination. Thus, oocyte growth and differentiation are genetically dissociable from the chromosomal events of meiosis. These findings open to study the independent contributions of meiosis and oocyte differentiation to the making of a functional egg.

The egg. The inside story of a cell

The egg, a fantastic little laboratory of molecular biology, has played a crucial role in redefining modern biology by moving it from the description of living things to the synthesis of living things (synthetic biology). Over the centuries, many hypotheses have been advanced concerning the egg's role in reproduction-from the preformation theory until von Baer's discovery to the present, with the 2012 Nobel Prize for Physiology or Medicine celebrating the egg as a totipotent stem cell able to reprogram fully differentiated somatic nuclei. The molecular dissection of its cytoplasmic components makes the egg an ideal bioreactor for several biotechnological applications, including pharmacological and food production sciences. In addition to its ubiquitous contribution to the worldwide diet, the egg, a powerful symbol, pervades philosophy, art, religion, and idiomatic expressions.

Embryonic stem cell-derived granulosa cells participate in ovarian follicle formation in vitro and in vivo

Differentiating embryonic stem cells (ESCs) can form ovarian follicle-like structures in vitro, consisting of an oocyte-like cell surrounded by somatic cells capable of steroidogenesis. Using a dual-fluorescence reporter system in which mouse ESCs express green fluorescent protein (GFP) under the control of a germ cell-specific Pou5f1 gene promoter and red fluorescent protein (Discosoma sp red [DsRed]) driven by the granulosa cell-specific Forkhead box L2 (Foxl2) gene promoter, we first confirmed in vitro formation of follicle-like structures containing GFP-positive cells surrounded by DsRed-positive cells. Isolated DsRed-positive cells specified from ECSs exhibited a gene expression profile consistent with granulosa cells, as revealed by the detection of messenger RNAs (mRNAs) for Foxl2, follistatin (Fst), anti-Müllerian hormone (Amh), and follicle-stimulating hormone receptor (Fshr) as well as by production of both progesterone and estradiol. In addition, treatment of isolated DsRed-expressing cells with follicle-stimulating hormone (FSH) significantly increased estradiol production over basal levels, confirming the presence of functional FSH receptors in these cells. Last, ESC-derived DsRed-positive cells injected into neonatal mouse ovaries became incorporated within the granulosa cell layer of immature follicles. These studies demonstrate that Foxl2-expressing ovarian somatic cells derived in vitro from differentiating ESCs express granulosa cell markers, actively associate with germ cells in vitro, synthesize steroids, respond to FSH, and participate in folliculogenesis in vivo.

Embryonic stem cell-derived granulosa cells participate in ovarian follicle formation in vitro and in vivo

Differentiating embryonic stem cells (ESCs) can form ovarian follicle-like structures in vitro, consisting of an oocyte-like cell surrounded by somatic cells capable of steroidogenesis. Using a dual-fluorescence reporter system in which mouse ESCs express green fluorescent protein (GFP) under the control of a germ cell-specific Pou5f1 gene promoter and red fluorescent protein (Discosoma sp red [DsRed]) driven by the granulosa cell-specific Forkhead box L2 (Foxl2) gene promoter, we first confirmed in vitro formation of follicle-like structures containing GFP-positive cells surrounded by DsRed-positive cells. Isolated DsRed-positive cells specified from ECSs exhibited a gene expression profile consistent with granulosa cells, as revealed by the detection of messenger RNAs (mRNAs) for Foxl2, follistatin (Fst), anti-Müllerian hormone (Amh), and follicle-stimulating hormone receptor (Fshr) as well as by production of both progesterone and estradiol. In addition, treatment of isolated DsRed-expressing cells with follicle-stimulating hormone (FSH) significantly increased estradiol production over basal levels, confirming the presence of functional FSH receptors in these cells. Last, ESC-derived DsRed-positive cells injected into neonatal mouse ovaries became incorporated within the granulosa cell layer of immature follicles. These studies demonstrate that Foxl2-expressing ovarian somatic cells derived in vitro from differentiating ESCs express granulosa cell markers, actively associate with germ cells in vitro, synthesize steroids, respond to FSH, and participate in folliculogenesis in vivo.

Aberrant gene expression and sexually incompatible genomic imprinting in oocytes derived from XY mouse embryonic stem cells in vitro

Mouse embryonic stem cells (ESCs) have the potential to differentiate into germ cells (GCs) in vivo and in vitro. Interestingly, XY ESCs can give rise to both male and female GCs in culture, irrespective of the genetic sex. Recent studies showed that ESC-derived primordial GCs contributed to functional gametogenesis in vivo; however, in vitro differentiation techniques have never succeeded in generating mature oocytes from ESCs due to cryptogenic growth arrest during the preantral follicle stages of development. To address this issue, a mouse ESC line, capable of producing follicle-like structures (FLSs) efficiently, was established to investigate their properties using conventional molecular biological methods. The results revealed that the ESC-derived FLSs were morphologically similar to ovarian primary-to-secondary follicles but never formed an antrum; instead, the FLSs eventually underwent abnormal development or cell death in culture, or formed teratomas when transplanted under the kidney capsule in mice. Gene expression analyses demonstrated that the FLSs lacked transcripts for genes essential to late folliculogenesis, including gonadotropin receptors and steroidogenic enzymes, whereas some other genes were overexpressed in FLSs compared to the adult ovary. The E-Cadherin protein, which is involved in cell-to-cell interactions, was also expressed ectopically. Remarkably, it was seen that oocyte-like cells in the FLSs exhibited androgenetic genomic imprinting, which is ordinarily indicative of male GCs. Although the FLSs did not express male GC marker genes, the DNA methyltransferase, Dnmt3L, was expressed at an abnormally high level. Furthermore, the expression of sex determination factors was ambiguous in FLSs as both male and female determinants were expressed weakly. These data suggest that the developmental dysfunction of the ESC-derived FLSs may be attributable to aberrant gene expression and genomic imprinting, possibly associated with uncertain sex determination in culture.

Expression of pluripotency and oocyte-related genes in single putative stem cells from human adult ovarian surface epithelium cultured in vitro in the presence of follicular fluid

The aim of this study was to trigger the expression of genes related to oocytes in putative ovarian stem cells scraped from the ovarian surface epithelium of women with premature ovarian failure and cultured in vitro in the presence of follicular fluid, rich in substances for oocyte growth and maturation. Ovarian surface epithelium was scraped and cell cultures were set up by scrapings in five women with nonfunctional ovaries and with no naturally present mature follicles or oocytes. In the presence of donated follicular fluid putative stem cells grew and developed into primitive oocyte-like cells. A detailed single-cell gene expression profiling was performed to elucidate their genetic status in comparison to human embryonic stem cells, oocytes, and somatic fibroblasts. The ovarian cell cultures depleted/converted reproductive hormones from the culture medium. Estradiol alone or together with other substances may be involved in development of these primitive oocyte-like cells. The majority of primitive oocyte-like cells was mononuclear and expressed several genes related to pluripotency and oocytes, including genes related to meiosis, although they did not express some important oocyte-specific genes. Our work reveals the presence of putative stem cells in the ovarian surface epithelium of women with premature ovarian failure.

Gene expression profiling of human oocytes developed and matured in vivo or in vitro

The quality of the human oocyte determines the success of fertilization and affects the consequent embryo development, pregnancy and birth; it therefore serves as a basis for human reproduction and fertility. The possibility to evaluate oocyte quality in the in vitro fertilization programme is very limited. The only criterion which is commonly used to evaluate oocyte quality is its morphology. There is a mass of oocytes in the in vitro fertilization programme which are not fertilized in spite of normal morphology. In the past, several attempts focused on oocyte gene expression profiling by different approaches. The results elucidated groups of genes related to the human oocyte. It was confirmed that some factors, such as oocyte in vitro maturation, are detectable at the molecular level of human oocytes and their polar bodies in terms of gene expression profile. Furthermore, the first genetic evaluations of oocyte-like cells developed in vitro from human stem cells of different origin were performed showing that these cells express some genes related to oocytes. All these findings provide some new knowledge and clearer insights into oocyte quality and oogenesis that might be introduced into clinical practice in the future.

Recovery of functional oocytes from cultured premeiotic germ cells after kidney capsule transplantation

The efficiency of in vitro culture systems for a premeiotic female germ cell is still low, mostly because of our incomplete understanding of the mechanisms controlling oogenesis and the obvious difficulties in reproducing the complex in vivo environment of such a process under in vitro conditions. Here we explored the possibility of recovering the developmental potential of mouse oocytes generated in vitro from premeiotic germ cells by transplantation under a kidney capsule of adult animals. To this aim, mouse embryonic ovaries of 12.5 days postcoitum cultured in vitro in a serum-free medium for 7 or 14 days, were transplanted beneath the kidney capsule of immunodeficient mice and analyzed after 21 (7+21 group) or 14 days (14+14 group). Cultured ovaries before transplantation showed delayed oocyte meiotic progression and follicle development. Interestingly, grafted ovaries of both groups, especially those of the 7+21 group, seemed able to restore the reproductive cycle of recipients. While the almost complete absence of primordial follicles was observed in grafted ovaries, oocytes from these ovaries showed transcript levels of genes associated to oocyte maturation similar to control. Moreover, the developmental stage of follicles and oocytes of the 7+21 group ovaries were comparable to that of 21 days post partum in vivo ovaries, whereas significant developmental delay were found in the 14+14 group ovaries. Nevertheless, oocytes retrieved from transplanted ovaries of both groups matured (around 80%) and were fertilized in vitro (around 20%-45%). Two-cell embryos from the fertilized oocytes developed to hatching blastocysts (about 50%) or gave rise to healthy live offspring (from 6% to 10%) when transplanted in a host mother. In conclusion, our results indicate that premeiotic female germ cells cultured in vitro up to primordial/primary follicle stages preserve their capability to complete oogenesis and can be fertilized and generate live pups after transplantation into a suitable in vivo environment.

Characterization of female germ-like cells derived from mouse embryonic stem cells through expression of GFP under the control of Figla promoter

Previous studies have demonstrated that germ cells can be derived from mouse embryonic stem cells (ESCs). However, there is still no efficient system, which can visualize the stage of germ cell specification in vitro, and further to identify and enrich germ cells derived from ESCs. Figla (factor in the germline, alpha) gene encodes a germ cell specific transcription factor that coordinates the expression of the oocyte-specific zona pellucida (Zp) genes and is essential for folliculogenesis in mouse. Here, we first constructed a pFigla-EGFP recombinant plasmid that expressed enhanced green fluorescent protein (EGFP) under the control of Figla promoter, and generated and characterized an ESC line stably carrying this pFigla-EGFP reporter construct. Then the ESCs were induced to differentiate into female germ-like cells by culturing adherent embryoid bodies (EBs) in retinoic acid (RA) induction medium or transplanting ESCs under the kidney capsule with ovarian cells. A population of differentiated ESCs expressed GFP, and these cells were analyzed by RT-PCR and immunofluorescence. The GFP positive cells showed the expression of germ cell markers Vasa, meiotic specific gene Stra8, Scp3, oocyte markers Gdf9, Zp3 and Figla, indicating that this method could be used for the purification and selection of female germ cells. Our study establishes a new selective system of female germ-like cell derivation and offers an approach for further research on the development and the differentiation of germ cells derived from stem cells.

Reprogramming and the mammalian germline: the Weismann barrier revisited

The germline represents a unique cell type that can transmit genetic material to the next generation. During early embryonic development, somatic cells give rise to a small population of cells known as germ cells, which eventually differentiate into mature gametes. Germ cells undergo a process of removing and resetting relevant epigenetic information, mainly by DNA demethylation. This extensive epigenetic reprogramming leads to the conversion of germ cells into immortal cells that can pass on the genome to the next generation. In the absence of germline-specific reprogramming, germ cells would preserve the old, parental epigenetic memory, which would prevent the transfer of heritable information to the offspring. On the contrary, somatic cells cannot reset epigenetic information by preserving the full methylation pattern on imprinting genes. In this review, we focus on the capacity of germ cells and somatic cells (soma) to transfer genetic information to the next generation, and thus revisit the Weismann theory of heredity.

Human aneuploidy: mechanisms and new insights into an age-old problem

Trisomic and monosomic (aneuploid) embryos account for at least 10% of human pregnancies and, for women nearing the end of their reproductive lifespan, the incidence may exceed 50%. The errors that lead to aneuploidy almost always occur in the oocyte but, despite intensive investigation, the underlying molecular basis has remained elusive. Recent studies of humans and model organisms have shed new light on the complexity of meiotic defects, providing evidence that the age-related increase in errors in the human female is not attributable to a single factor but to an interplay between unique features of oogenesis and a host of endogenous and exogenous factors.

The next (re)generation of ovarian biology and fertility in women: is current science tomorrow's practice?

Stem cell-based strategies for ovarian regeneration and oocyte production have been proposed as future clinical therapies for treating infertility in women. However, utilization of embryonic stem cells or induced pluripotent stem cells to produce oocytes has had limited success in vitro. A recent report of the isolation and characterization of endogenous oocyte-producing or oogonial stem cells (OSCs) from ovaries of reproductive age women describes the first stable and pure human female germ cell culture model in which a subset of cells appear to initiate and complete meiosis. In addition, purified human OSCs introduced into adult human ovarian cortical tissue generate oocytes that arrest at the diplotene stage of meiosis and successfully recruit granulosa cells to form new primordial follicles. This overview examines the current landscape of in vitro and in vivo gametogenesis from stem cells, with emphasis on generation of human oocytes. Future research objectives for this area of work, as well as potential clinical applications involving the use of human OSCs, are discussed.

Meiotic competent human germ cell-like cells derived from human embryonic stem cells induced by BMP4/WNT3A signaling and OCT4/EpCAM (epithelial cell adhesion molecule) selection

The establishment of an effective germ cell selection/enrichment platform from in vitro differentiating human embryonic stem cells (hESCs) is crucial for studying the molecular and signaling processes governing human germ cell specification and development. In this study, we developed a germ cell-enriching system that enables us to identify signaling factors involved in germ cell-fate induction from differentiating hESCs in vitro. First, we demonstrated that selection through an OCT4-EGFP reporter system can successfully increase the percentage of meiotic-competent, germ cell-like cells from spontaneously differentiating hESCs. Furthermore, we showed that the pluripotency associated surface marker, epithelial cell adhesion molecule (EpCAM), is also expressed in human fetal gonads and can be used as an effective selection marker for germ cell enrichment from differentiating hESCs. Combining OCT4 and EpCAM selection can further enrich the meiotic-competent germ cell-like cell population. Also, with the percentage of OCT4(+)/EpCAM(+) cells as readout, we demonstrated the synergistic effect of BMP4/pSMAD1/5/8 and WNT3A/β-CATENIN in promoting hESCs toward the germline fate. Combining BMP4/WNT3A induction and OCT4/EpCAM selection can significantly increase the putative germ cell population with meiotic competency. Co-transplantation of these cells with dissociated mouse neonatal ovary cells into SCID mice resulted in a homogenous germ cell cluster formation in vivo. The stepwise platform established in this study provides a useful tool to elucidate the molecular mechanisms of human germ cell development, which has implications not only for human fertility research but regenerative medicine in general.

Oocyte formation by mitotically active germ cells purified from ovaries of reproductive-age women

Germline stem cells that produce oocytes in vitro and fertilization-competent eggs in vivo have been identified in and isolated from adult mouse ovaries. Here we describe and validate a FACS-based protocol that can be used with adult mouse ovaries and human ovarian cortical tissue to purify rare mitotically-active cells that exhibit a gene expression profile consistent with primitive germ cells. Once established in vitro, these cells can be expanded for months and spontaneously generate 35–50 µm oocytes, as determined by morphology, gene expression and attainment of haploid (1n) status. Injection of the human germline cells, engineered to stably express GFP, into human ovarian cortical biopsies leads to formation of follicles containing GFP-positive oocytes 1–2 weeks after xenotransplantation into immunodeficient female mice. Thus, ovaries of reproductive-age women, like adult mice, possess rare mitotically-active germ cells that can be propagated in vitro as well as generate oocytes in vitro and in vivo.

Ovarian stem cell niche and follicular renewal in mammals

Stem cell niche consists of perivascular compartment, which connects the stem cells to the immune and vascular systems. During embryonic period, extragonadal primordial germ cells colonize coelomic epithelium of developing gonads. Subsequently, ovarian stem cells (OSC) produce secondary germ cells under the influence of OSC niche, including immune system-related cells and hormonal signaling. The OSC in fetal and adult human ovaries serve as a source of germ and granulosa cells. Lack of either granulosa or germ cell niche will result in premature ovarian failure in spite of the presence of OSC. During perinatal period, the OSC transdifferentiate into fibroblast-like cells forming the ovarian tunica albuginea resistant to environmental threats. They represent mesenchymal precursors of epithelial OSC during adulthood. The follicular renewal during the prime reproductive period (PRP) ensures that there are fresh eggs available for a healthy progeny. End of PRP is followed by exponentially growing fetal genetic abnormalities. The OSC are present in adult, aging, and postmenopausal ovaries, and differentiate in vitro into new oocytes. During in vitro development of large isolated oocytes reaching 200 μm in diameter, an ancestral mechanism of premeiotic nurse cells, which operates during oogenesis in developing ovaries from invertebrates to mammalian species, is utilized. In vitro developed eggs could be used for autologous IVF treatment of premature ovarian failure. Such eggs are also capable to produce parthenogenetic embryos like some cultured follicular oocytes. The parthenotes produce embryonic stem cells derived from inner cell mass, and these cells can serve as autologous pluripotent stem cells.

Generation of human female reproductive tract epithelium from human embryonic stem cells

Background

Recent studies have identified stem/progenitor cells in human and mouse uterine epithelium, which are postulated to be responsible for tissue regeneration and proliferative disorders of human endometrium. These progenitor cells are thought to be derived from Müllerian duct (MD), the primordial female reproductive tract (FRT).

Methodology/Principal Findings

We have developed a model of human reproductive tract development in which inductive neonatal mouse uterine mesenchyme (nMUM) is recombined with green fluorescent protein (GFP)-tagged human embryonic stem cells (hESCs); GFP-hESC (ENVY). We demonstrate for the first time that hESCs can be differentiated into cells with a human FRT epithelial cell phenotype. hESC derived FRT epithelial cells emerged from cultures containing MIXL1⁺ mesendodermal precursors, paralleling events occurring during normal organogenesis. Following transplantation, nMUM treated embryoid bodies (EBs) generated epithelial structures with a typical MD phenotype that expressed the MD markers PAX2, HOXA10. Functionally, the hESCs derived FRT epithelium responded to exogenous estrogen by proliferating and secreting uterine-specific glycodelin A (GdA).

Conclusions/Significance

These data show nMUM can induce differentiation of hESC to form the FRT epithelium. This may provide a model to study early developmental events of the human FRT.