Comparative evaluation of different in vitro systems that stimulate germ cell differentiation in human embryonic stem cells

Menstrual blood-derived endometrial stem cell, a unique and promising alternative in the stem cell-based therapy for chemotherapy-induced premature ovarian insufficiency

Chemotherapy can cause ovarian dysfunction and infertility since the ovary is extremely sensitive to chemotherapeutic drugs. Apart from the indispensable role of the ovary in the overall hormonal milieu, ovarian dysfunction also affects many other organ systems and functions including sexuality, bones, the cardiovascular system, and neurocognitive function. Although conventional hormone replacement therapy can partly relieve the adverse symptoms of premature ovarian insufficiency (POI), the treatment cannot fundamentally prevent deterioration of POI. Therefore, effective treatments to improve chemotherapy-induced POI are urgently needed, especially for patients desiring fertility preservation. Recently, mesenchymal stem cell (MSC)-based therapies have resulted in promising improvements in chemotherapy-induced ovary dysfunction by enhancing the anti-apoptotic capacity of ovarian cells, preventing ovarian follicular atresia, promoting angiogenesis and improving injured ovarian structure and the pregnancy rate. These improvements are mainly attributed to MSC-derived biological factors, functional RNAs, and even mitochondria, which are directly secreted or indirectly translocated with extracellular vesicles (microvesicles and exosomes) to repair ovarian dysfunction. Additionally, as a novel source of MSCs, menstrual blood-derived endometrial stem cells (MenSCs) have exhibited promising therapeutic effects in various diseases due to their comprehensive advantages, such as periodic and non-invasive sample collection, abundant sources, regular donation and autologous transplantation. Therefore, this review summarizes the efficacy of MSCs transplantation in improving chemotherapy-induced POI and analyzes the underlying mechanism, and further discusses the benefit and existing challenges in promoting the clinical application of MenSCs in chemotherapy-induced POI.

Oocyte Arrested at Metaphase II Stage were Derived from Human Pluripotent Stem Cells in vitro

Initiation of meiosis is the most difficult aspect of inducing competent oocytes differentiation from human stem cells in vitro. Human induced pluripotent stem cells (hiPSCs) and embryonic stem cells (hESCs) were cultured with follicle fluid, cytokines and small molecule to induced oocyte-like cells (OLCs) formation through a three-step induction procedure. Expression of surface markers and differentiation potential of germ cells were analyzed in vitro by flow cytometry, gene expression, immunocytochemistry, western blotting and RNA Sequencing. To induce the differentiation of hiPSCs into OLCs, cells were firstly cultured with a primordial germ cell medium for 10 days. The cells exhibited similar morphological features to primordial germ cells (PGCs), high expressing of germ cell markers and primordial follicle development associated genes. The induced PGCs were then cultured with the primordial follicle-like cell medium for 5 days to form the induced follicle-like structures (iFLs), which retained both primordial oocytes-like cells and granulosa-like cells. In the third step, the detached iFLs were harvested and transferred to the OLC-medium for additional 10 days. The cultured cells developed cumulus-oocyte-complexes (COCs) structures and OLCs with different sizes (50-150 μm diameter) and a zona pellucida. The in vitro matured OLCs had polar bodies and were arrested at metaphase II (MII) stage. Some OLCs were self-activated and spontaneously developed into multiple-cell structures similar to preimplantation embryos, indicating that OLCs were parthenogenetically activated though in vitro fertilization potential of OLCs are yet to be proved. in vitro maturation of OLCs derived from hiPSCs provides a new means to study human germ cell formation and oogenesis.

Comparative effects of retinoic acid, granulosa cells conditioned medium or forskolin in combination with granulosa cell co-culturing on mouse germ cell differentiation

BACKGROUND

Devising of an appropriate in vitro culture method for germ cells differentiation in the presence of soluble factors has attracted considerable attention, which results will provide new insight into reproductive biology. In this study, we compared the effects of forskolin, retinoic acid (RA) or granulosa cell-conditioned medium in the presence or absence of granulosa cell co-culturing on germ cell differentiation from embryonic stem cells (ESCs).

METHODS AND RESULTS

Embryonic stem cells were differentiated using embryoid bodies (EBs) for 5 days, and then EB-derived cells were co-cultured with or without adult mouse granulosa cells using monolayer protocol and treated with 50 µM forskolin, 1 µM RA and 50% granulosa cell-conditioned medium for 4 days. Granulosa cell-conditioned medium significantly increased the levels of Scp3, Rec8, Mvh and Gdf9 expression in the granulosa cell co-culture method compared to untreated cells. A significant elevation of Stra8, Rec8 and Mvh was observed after treatment with RA in the absence of granulosa cells and there was no significant increase in the levels of expression of germ cell-specific genes after treatment with forskolin compared to control. Furthermore, forskolin and RA significantly increased viability and proliferation of germ-like cells, compared with granulosa cell-conditioned medium.

CONCLUSIONS

Our study revealed that granulosa cell-conditioned medium and RA effectively can induce germ cell differentiation from ESCs, however combined application of granulosa cell-conditioned medium and co-culturing with granulosa cells had synergic effect on germ cell development in vitro as optimized protocol.

Meiosis resumption in human primordial germ cells from induced pluripotent stem cells by in vitro activation and reconstruction of ovarian nests

Background

The differentiation of human induced pluripotent stem cells (iPSCs) into oocytes, which involves the transformation from mitosis to meiosis, has been a hotspot of biological research for many years and represents a desirable experimental model and potential strategy for treating infertility. At present, studies have shown that most cells stagnate in the oogonium stage after differentiation into primordial germ cells (PGCs) from human iPSCs.

Methods

iPSCs carrying a SYCP3-mkate2 knock-in reporter were generated by the CRISPR/Cas9 strategy to monitor meiosis status during induced differentiation from iPSCs into oocytes. These induced PGCs/oogonia were activated by small molecules from the Wnt signaling pathway and then cocultured with reconstructed human ovarian nests in vivo for further development.

Results

First, human PGCs and oogonia were efficiently induced from iPSCs. Second, induced dormant PGCs resumed meiosis and then differentiated into primary oocytes through the in vitro activation of the Wnt signaling pathway. Finally, a new coculture system involving the reconstruction of ovarian nests in vitro could facilitate the differentiation of oocytes.

Conclusions

Human PGCs/oogonia induced from iPSCs can be activated and used to resume meiosis by molecules of the Wnt signaling pathway. The coculture of activated PGCs and reconstruction of ovarian nests facilitated differentiation into primary oocytes and the generation of haploid human oocytes in vivo. These findings established a new strategy for germline competence in primary oocytes and provided a keystone for human gametogenesis in vitro and in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03019-3.

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

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

The safety of VASApos presumptive adult ovarian stem cells

Isolation and characterization of presumptive human adult ovarian stem cells (OSC) has broken the long standing dogma of the absence of postnatal neo-oogenesis. Human adult OSC have been immunosorted by antibodies reacting against the RNA helicase VASA and have been reported to engraft into appropriate stem cell niches to promote neo-oogenesis. Analysis of published research, however, questions some of the findings on isolation, characterization, in-vitro self-renewal and clinical safety of the presumptive human adult OSC. In the present study, human VASA^pos embryo-fetal primordial germ cells and presumptive adult OSC are shown to share several pluripotency and early germ cell markers not ascertained in the initial characterization of adult OSC. A new hypothesis is made that the restoration of fertility claimed to result from presumptive human adult OSC may be attributed instead to VASA^pos embryo-fetal primordial germ cell remnants in the adult ovary, or alternatively to earlier VASA^neg germ cells generated by in-vitro de-differentiation of the presumptive OSC. The suggested hypotheses have extensive implications for the practice and safety of adult OSC in the development of new treatments aimed at rescuing the ovarian reserve.

Regenerative Medicine Approaches in Bioengineering Female Reproductive Tissues

Diseases, disorders, and dysfunctions of the female reproductive tract tissues can result in either infertility and/or hormonal imbalance. Current treatment options are limited and often do not result in tissue function restoration, requiring alternative therapeutic approaches. Regenerative medicine offers potential new therapies through the bioengineering of female reproductive tissues. This review focuses on some of the current technologies that could address the restoration of functional female reproductive tissues, including the use of stem cells, biomaterial scaffolds, bio-printing, and bio-fabrication of tissues or organoids. The use of these approaches could also be used to address issues in infertility. Strategies such as cell-based hormone replacement therapy could provide a more natural means of restoring normal ovarian physiology. Engineering of reproductive tissues and organs could serve as a powerful tool for correcting developmental anomalies. Organ-on-a-chip technologies could be used to perform drug screening for personalized medicine approaches and scientific investigations of the complex physiological interactions between the female reproductive tissues and other organ systems. While some of these technologies have already been developed, others have not been translated for clinical application. The continuous evolution of biomaterials and techniques, advances in bioprinting, along with emerging ideas for new approaches, shows a promising future for treating female reproductive tract-related disorders and dysfunctions.

Human Pluripotent Stem Cells in Reproductive Science-a Comparison of Protocols Used to Generate and Define Male Germ Cells from Pluripotent Stem Cells

Globally, fertility-related issues affect around 15% of couples. In 20%–30% of cases men are solely responsible, and they contribute in around 50% of all cases. Hence, understanding of in vivo germ-cell specification and exploring different angles of fertility preservation and infertility intervention are considered hot topics nowadays, with special focus on the use of human pluripotent stem cells (hPSCs) as a source of in vitro germ-cell generation. However, the generation of male germ cells from hPSCs can currently be considered challenging, making a judgment on the real perspective of these innovative approaches difficult. Ever since the first spontaneous germ-cell differentiation studies, using human embryonic stem cells, various strategies, including specific co-cultures, gene over-expression, and addition of growth factors, have been applied for human germ-cell derivation. In line with the variety of differentiation methods, the outcomes have ranged from early and migratory primordial germ cells up to post-meiotic spermatids. This variety of culture approaches and cell lines makes comparisons between protocols difficult. Considering the diverse strategies and outcomes, we aim in this mini-review to summarize the literature regarding in vitro derivation of human male germ cells from hPSCs, while keeping a particular focus on the culture methods, growth factors, and cell lines used.

Genetic studies in mice directly link oocytes produced during adulthood to ovarian function and natural fertility

Multiple labs have reported that mammalian ovaries contain oogonial stem cells (OSCs), which can differentiate into oocytes that fertilize to produce offspring. However, the physiological relevance of these observations to adult ovarian function is unknown. Here we performed targeted and reversible ablation of premeiotic germ cells undergoing differentiation into oocytes in transgenic mice expressing the suicide gene, herpes simplex virus thymidine kinase (HSVtk), driven by the promoter of stimulated by retinoic acid gene 8 (Stra8), a germ cell-specific gene activated during meiotic commitment. Over a 21-day ablation phase induced by the HSVtk pro-drug, ganciclovir (GCV), oocyte numbers declined due to a disruption of new oocyte input. However, germ cell differentiation resumed after ceasing the ablation protocol, enabling complete regeneration of the oocyte pool. We next employed inducible lineage tracing to fate map, through Cre recombinase-mediated fluorescent reporter gene activation only in Stra8-expressing cells, newly-formed oocytes. Induction of the system during adulthood yielded a mosaic pool of unmarked (pre-existing) and marked (newly-formed) oocytes. Marked oocytes matured and fertilized to produce offspring, which grew normally to adulthood and transmitted the reporter to second-generation offspring. These findings establish that oocytes generated during adulthood contribute directly to ovarian function and natural fertility in mammals.

Overexpression of Oct4 in porcine ovarian stem/stromal cells enhances differentiation of oocyte-like cells in vitro and ovarian follicular formation in vivo

Background

Recent findings have revealed that the female gonad may have regenerative activity with having germ line stem cells in juveniles and adults. Application of these germ line stem cells could be an alternative therapy for reproductive disorders in regenerative medicine.

Methods

To enhance the potency of differentiation into oocyte-like cells (OLCs) and folliculogenesis, we overexpressed Oct4 in ovarian stem/stromal cell (OvSCs) and examined the cellular properties related to stemness and self-renewal ability and finally demonstrated the ability of in vitro differentiation and folliculogenesis.

Results

Ovarian cortex included putative stem cells in terms of AP activity, cell cycle status, cell proliferation, expression of mesenchymal lineage surface markers and pluripotent transcriptional markers. Further, Oct4 transfected OvSCs (Oct4-OvSCs) were enhanced their AP activity and cell proliferation compared to OvSCs. The potential on in vitro differentiation into OLCs and in vivo folliculogenesis was also evaluated in OvSCs and Oct4-OvSCs, respectively. Oct4-OvSCs possessed higher oogenesis potential in vitro than OvSCs, in terms of expression of germ cell markers by RT-PCR and the number of OLCs. When OvSCs and Oct4-OvSCs were xeno-transplanted into infertile mice ovaries, the OvSCs transplantation induced new primary follicle formation and hormonal levels of estradiol and FSH remained similar to that of normal mice. However, Oct4-OvSCs possessed higher ability for folliculogenesis based on inducing developing follicles with thecal layer and granulosa cells and more similar estradiol level to normal mice.

Conclusions

These findings demonstrated that putative stem cells were present in ovarian cortex and exhibited differentiation ability into OLCs and folliculogenesis in vivo, and Oct4-overexpression enhanced these ability, suggesting their cellular models based on gene therapy in understanding the mechanisms of oogenesis and folliculogenesis, and finally in view of reproductive cell therapy.

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.

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.

Human amniotic fluid stem cells possess the potential to differentiate into primordial follicle oocytes in vitro

Previous reports have demonstrated that embryonic stem cells were capable of differentiating into primordial germ cells through the formation of embryoid bodies that subsequently generated oocyte-like cells (OLCs). Such a process could facilitate studies of primordial follicle oocyte development in vitro and regenerative medicine. To investigate the pluripotency of human amniotic fluid stem cells (hAFSCs) and their ability to differentiate into germ cells, we isolated a CD117(+)/CD44(+) hAFSC line that showed fibroblastoid morphology and intrinsically expressed both stem cell markers (OCT4, NANOG, SOX2) and germ cell markers (DAZL, STELLA). To encourage differentiation into OLCs, the hAFSCs were first cultured in a medium supplemented with 5% porcine follicular fluid for 10 days. During the induction period, cell aggregates formed and syntheses of steroid hormones were detected; some OLCs and granulosa cell-like cells could be loosened from the surface of the culture dish. Cell aggregates were collected and replated in oocyte culture medium for an additional 7-10 days. OLCs ranging from 50 to 120 μm presenting zona pellucida were observed in cumulus-oocyte complexes; some OLCs developed spontaneously into multicell structures similar to preimplantation embryos. Approximately 2% of the hAFSCs differentiated to meiotic germ cells that expressed folliculogenesis- and oogenesis-associated markers. Although the in vitro maturation and fertilization potentials are as yet unproven, short-term (<25 days) and high-efficiency (>2%) derivation of OLCs from hAFSCs might provide a new approach to the study of human germ cell development in vitro.

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.

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.

Differentiation of stem cells upon deprivation of exogenous FGF2: a general approach to study spontaneous differentiation of hESCs in vitro

Establishing a model for in vitro differentiation of human embryonic stem cells (hESCs) towards the germ cell lineage could be used to identify molecular mechanisms behind germ cell differentiation that may help in understanding human infertility. Here, we evaluate whether a lack of exogenous fibroblast growth factor 2 (FGF2) is supporting spontaneous differentiation of hESCs cultured on human foreskin fibroblast (hFF) monolayers towards germ cell lineage. Additionally to depriving the hESCs of exogenous FGF2, cells were stimulated with all-trans retinoic acid (ATRA). To get a more comprehensive impression on effects of removal of FGF2 and stimulation with ATRA, we combined the results of three cell lines for each experimental setting. When combining gene expression profiles of three cell lines for 96 genes, only 6 genes showed a significant up-regulation in all cell lines, when no FGF2 was added to the media for 12 weeks. None of these genes are related to the germ lineage, whereas genes for neuronal cells (PAX6 and NR6A1) and endothelial cells (FLT-1 and PTF1A) were up-regulated. To induce and support the differentiation towards the germ lineage we stimulated hESCs with different concentrations of ATRA for 7 and 14 days. We observed no significant difference in gene expression on RNA level when combining all cell lines. Whereas, the overall outcome was negative, one of these cell lines demonstrated an up-regulation of DDX4 on RNA and protein level after 7 days of ATRA stimulation. In summary, our data showed that the lack of exogenous FGF2 results in up-regulation of genes crucial for neuronal and endothelial cell differentiation of hESCs, but not in the up-regulation of genes related to germ cell differentiation when cultured on hFFs. Additionally, we demonstrated that ATRA supplementation did not result in a general specific direction of hESCs towards the germ lineage.

Molecular signatures to define spermatogenic cells in common marmoset (Callithrix jacchus)

Germ cell development is a fundamental process required to produce offspring. The developmental program of spermatogenesis has been assumed to be similar among mammals. However, recent studies have revealed differences in the molecular properties of primate germ cells compared with the well-characterized mouse germ cells. This may prevent simple application of rodent insights into higher primates. Therefore, thorough investigation of primate germ cells is necessary, as this may lead to the development of more appropriate animal models. The aim of this study is to define molecular signatures of spermatogenic cells in the common marmoset, Callithrix jacchus. Interestingly, NANOG, PRDM1, DPPA3 (STELLA), IFITM3, and ZP1 transcripts, but no POU5F1 (OCT4), were detected in adult marmoset testis. Conversely, mouse testis expressed Pou5f1 but not Nanog, Prdm1, Dppa3, Ifitm3, and Zp1. Other previously described mouse germ cell markers were conserved in marmoset and mouse testes. Intriguingly, marmoset spermatogenic cells underwent dynamic protein expression in a developmental stage-specific manner; DDX4 (VASA) protein was present in gonocytes, diminished in spermatogonial cells, and reexpressed in spermatocytes. To investigate epigenetic differences between adult marmoset and mice, DNA methylation analyses identified unique epigenetic profiles to marmoset and mice. Marmoset NANOG and POU5F1 promoters in spermatogenic cells exhibited a methylation status opposite to that in mice, while the DDX4 and LEFTY1 loci, as well as imprinted genes, displayed an evolutionarily conserved methylation pattern. Marmosets have great advantages as models for human reproductive biology and are also valuable as experimental nonhuman primates; thus, the current study provides an important platform for primate reproductive biology, including possible applications to humans.

Label-free detection of surface markers on stem cells by oblique-incidence reflectivity difference microscopy

Conventional fluorescence microscopy is routinely used to detect cell surface markers through fluorophore-conjugated antibodies. However, fluorophore-conjugation of antibodies alters binding properties such as strength and specificity of the antibody in often uncharacterized ways. Here we present a method using an oblique-incidence reflectivity difference (OI-RD) microscope for label-free, real-time detection of cell surface markers, and apply it to analysis of stage-specific embryonic antigen 1 (SSEA1) on stem cells. Mouse stem cells express SSEA1 on their surfaces, and the level of SSEA1 decreases when the cells start to differentiate. In this study, we immobilized mouse stem cells and non-stem cells (control) on a glass surface as a microarray and reacted the cell microarray with unlabeled SSEA1 antibodies. By monitoring the reaction with an OI-RD microscope in real time, we confirmed that the SSEA1 antibodies bind only to the surface of the stem cells and not to the surface of non-stem cells. From the binding curves, we determined the equilibrium dissociation constant (Kd) of the antibody with the SSEA1 markers on the stem cell surface. Thus, the OI-RD microscope can be used to detect binding affinities between cell surface markers and unlabeled antibodies bound to the cells; this information could be useful for determination of stem cell stages.

Sertoli cell-conditioned medium induces germ cell differentiation in human embryonic stem cells

PURPOSE

To investigate the spontaneous germ cell differentiation capacity of VUB hESC lines, develop a protocol for the induction of germ cell differentiation using conditioned medium from Sertoli cells (SCCM) and compare it to existing protocols.

METHODS

hESC were allowed to differentiate spontaneously or after the addition of bone morphogenetic proteins (BMPs) and/or SCCM. VASA transcripts were measured by relative quantification real-time RT-PCR to determine the efficiency of germ cell differentiation.

RESULTS

VUB hESC lines can differentiate spontaneously towards the germ cell lineage, however, more consistently in an embryoid body approach than in monolayer cultures. BMPs and SCCM significantly improve VASA expression, but do not have a synergistic effect. Direct contact of differentiating hESC with Sertoli cells does not improve VASA expression.

CONCLUSIONS

SCCM contains inductive factors for germ cell differentiation and could represent an element for in-vitro differentiation to germ cells.