Isolation of small SSEA-4-positive putative stem cells from the ovarian surface epithelium of adult human ovaries by two different methods

Which Side of the Coin Are You on Regarding Possible Postnatal Oogenesis?

It is well known that oocytes are produced during fetal development and that the total number of primary follicles is determined at birth. In humans, there is a constant loss of follicles after birth until about two years of age. The number of follicles is preserved until the resumption of meiosis at puberty and there is no renewal of the oocytes; this dogma was maintained in the last century because there were no suitable techniques to detect and obtain stem cells. However, following stem cell markers, several scientists have detected them in developing and adult human ovarian tissues, especially in the ovarian surface epithelial cells. Furthermore, many authors using different methodological strategies have indicated this possibility. This evidence has led many scientists to explore this hypothesis; there is no definitive consensus to accept this idea. Interestingly, oocyte retrieval from mature ovaries and other tissue sources of stem cells has contributed to the development of strategies for the retrieval of mature oocytes, useful for assisted reproductive technology. Here, we review the evidence and controversies on oocyte neooogenesis in adult women; in addition, we agree with the idea that this process may occur in adulthood and that its alteration may be related to various pathologies in women, such as polycystic ovary syndrome, premature ovarian insufficiency, diminished ovarian reserve and several infertility and genetic disorders.

Glycan diversity in ovarian cancer: Unraveling the immune interplay and therapeutic prospects

Ovarian cancer remains a formidable challenge in oncology due to its late-stage diagnosis and limited treatment options. Recent research has revealed the intricate interplay between glycan diversity and the immune microenvironment within ovarian tumors, shedding new light on potential therapeutic strategies. This review seeks to investigate the complex role of glycans in ovarian cancer and their impact on the immune response. Glycans, complex sugar molecules decorating cell surfaces and secreted proteins, have emerged as key regulators of immune surveillance in ovarian cancer. Aberrant glycosylation patterns can promote immune evasion by shielding tumor cells from immune recognition, enabling disease progression. Conversely, certain glycan structures can modulate the immune response, leading to either antitumor immunity or immune tolerance. Understanding the intricate relationship between glycan diversity and immune interactions in ovarian cancer holds promise for the development of innovative therapeutic approaches. Immunotherapies that target glycan-mediated immune evasion, such as glycan-based vaccines or checkpoint inhibitors, are under investigation. Additionally, glycan profiling may serve as a diagnostic tool for patient stratification and treatment selection. This review underscores the emerging importance of glycan diversity in ovarian cancer, emphasizing the potential for unraveling immune interplay and advancing tailored therapeutic prospects for this devastating disease.

Unveiling the Differentiation Potential of Ovarian Theca Interna Cells from Multipotent Stem Cell-like Cells

RESEARCH QUESTION

Theca interna cells (TICs) are an indispensable cell source for ovarian follicle development and steroidogenesis. Recent studies have identified theca stem cells (TSCs) in both humans and animals. Interestingly, TSCs express mesenchymal stem cell (MSC)-related markers and can differentiate into mesenchymal lineages. MSCs are promising for tissue engineering and regenerative medicine due to their self-renewal and differentiation abilities. Therefore, this study investigated the potential origin of TICs from MSCs.

DESIGN

Whole ovaries from postmenopausal organ donors were obtained, and their cortex was cryopreserved prior to the isolation of stromal cells. These isolated cells were differentiated in vitro to TICs using cell media enriched with various growth factors and hormones. Immunocytochemistry, an enzyme-linked immunosorbent assay, flow cytometry, and reverse transcription-quantitative polymerase chain were employed at different timepoints. Data were analyzed using one-way ANOVA.

RESULTS

Immunocytochemistry showed an increase in TIC markers from day 0 to day 8 and a significant rise in MSC-like markers on day 2. This corresponds with rising androstenedione levels from day 2 to day 13. Flow cytometry identified a decreasing MSC-like cell population from day 2 onwards. The CD13+ cell population and its gene expression increased significantly over time. NGFR and PDGFRA expression was induced on days 0 and 2, respectively, compared to day 13.

CONCLUSIONS

This study offers insights into MSC-like cells as the potential origin of TICs. Differentiating TICs from these widely accessible MSCs holds potential significance for toxicity studies and investigating TIC-related disorders like polycystic ovary syndrome (PCOS).

Identification and characterization of multipotential stem cells in immortalized normal ovarian surface epithelial cells

The ovarian surface epithelium (OSE) is a single layer of squamous-to-cuboidal epithelial cells that experience repetitive ovulatory rupture and subsequent repair. However, the characteristics of human immortalized ovarian surface epithelial cells (IOSE80) remain elusive. This study aims to determine whether IOSE80 cells have the characteristics of stem cell proliferation and multilineage differentiation and their application in regenerative medicine. IOSE80 cells are sequenced by high-throughput transcriptome analysis, and 5 sets of public data are used to compare the differences between IOSE80 cells and bone marrow mesenchymal stem cells, pluripotent stem cells, and oocytes in transcriptome profiling. The IOSE80 cells present a cobblestone-like monolayer and express the epithelial cell marker KRT18; the stem cell markers IFITM3, ALDH1A1, and VIM; lowly express stem cell marker LGR5 and germ cell markers DDX4 and DAZL. In addition, the GO terms "regulation of stem cell proliferation", "epithelial cell proliferation", etc., are significantly enriched ( P<0.05). IOSE80 cells have the potential to act as mesenchymal stem cells to differentiate into adipocytes with lipid droplets, osteoblasts, and chondroblasts in vitro. IOSE80 cells express pluripotent stem cell markers, including OCT4, SSEA4, TRA-1-60, and TRA-1-81, and they can be induced into three germ layers in vitro. IOSE80 cells also form oocyte-like cells in vitro and in vivo. In addition, IOSE80 cells exhibit robust proliferation, migration, and ovarian repair functions after in vivo transplantation. This study demonstrates that IOSE80 cells have the characteristics of pluripotent/multipotent stem cells, indicating their important role in tissue engineering and regenerative medicine.

Smaller size packs a stronger punch - Recent advances in small antibody fragments targeting tumour-associated carbohydrate antigens

Attached to proteins, lipids, or forming long, complex chains, glycans represent the most versatile post-translational modification in nature and surround all human cells. Unique glycan structures are monitored by the immune system and differentiate self from non-self and healthy from malignant cells. Aberrant glycosylations, termed tumour-associated carbohydrate antigens (TACAs), are a hallmark of cancer and are correlated with all aspects of cancer biology. Therefore, TACAs represent attractive targets for monoclonal antibodies for cancer diagnosis and therapy. However, due to the thick and dense glycocalyx as well as the tumour micro-environment, conventional antibodies often suffer from restricted access and limited effectiveness in vivo. To overcome this issue, many small antibody fragments have come forth, showing similar affinity with better efficiency than their full-length counterparts. Here we review small antibody fragments against specific glycans on tumour cells and highlight their advantages over conventional antibodies.

Does the ovarian surface epithelium differentiate into primordial follicle and primary follicle precursor structures?

Purpose: The aim of this study is to investigate the differentiation capacity of ovarian surface epithelial cells both in cell culture conditions and in ovarian tissue sections. Materials and Methods: The ovaries of two prepubertal (4 weeks old) female rats were divided into small pieces and explant cell culture was created. Ovarian surface epithelium proliferating together with ovarian stromal cells in mixed cell culture was isolated and reproduced. In addition, ovarian surface epithelium was examined in histological sections of ovarian tissue and images were taken under the microscope. Results: The morphological appearance of the ovarian surface epithelium was found to be cobblestone. In the count performed under phase contrast microscopy, it was observed that 2x106 and 3x106 cells were grown in the culture dishes, respectively. Primordial follicle-like structures were observed in some areas of the petri dishes. On the histological sections, primordial and primary follicle precursor structures were observed on the basement membrane. Conclusion: Showing oocyte markers (Gdf-9, C-Mos, Zpc, Stella) and germ cell markers (Dazl, Vasa, Blimp1, Fragilis) both in cell cultures and in histological sections can give us valuable information in terms of monitoring the differentiation capacity of these cells.

Artificial Oocyte: Development and Potential Application

Millions of people around the world suffer from infertility, with the number of infertile couples and individuals increasing every year. Assisted reproductive technologies (ART) have been widely developed in recent years; however, some patients are unable to benefit from these technologies due to their lack of functional germ cells. Therefore, the development of alternative methods seems necessary. One of these methods is to create artificial oocytes. Oocytes can be generated in vitro from the ovary, fetal gonad, germline stem cells (GSCs), ovarian stem cells, or pluripotent stem cells (PSCs). This approach has raised new hopes in both basic research and medical applications. In this article, we looked at the principle of oocyte development, the landmark studies that enhanced our understanding of the cellular and molecular mechanisms that govern oogenesis in vivo, as well as the mechanisms underlying in vitro generation of functional oocytes from different sources of mouse and human stem cells. In addition, we introduced next-generation ART using somatic cells with artificial oocytes. Finally, we provided an overview of the reproductive application of in vitro oogenesis and its use in human fertility.

Identification of Stem Cell-Like Cells in the Ovary

Understanding the function of stem cells and cellular microenvironments in in vitro oogenesis, including ovarian folliculogenesis, is crucial for reproductive biology. Because mammalian females cannot generate oocytes after birth, the number of oocyte decreases with the progression of reproductive age. Meanwhile, there is an emerging need for the neogenesis of female germ cells to treat the increasing infertility-related issues in cancer survivors. The concept of oocytes neogenesis came from the promising results of stem cells in reproductive medicine. The stem cells that generate oocytes are defined as stem cell-like cells in the ovary (OSCs). Several recent studies have focused on the origin, isolation, and characteristic of OSCs and the differentiation of OSCs into oocytes, ovarian follicles and granulosa cells. Hence, in this review, we focus on the experimental trends in OSC research and discuss the methods of OSC isolation. We further summarized the characteristics of OSCs and discuss the markers used to identify OSCs differentiated from various cell sources. We believe that this review will be beneficial for advancing the research and clinical applications of OSCs.

Why double ovarian stimulation in an in vitro fertilization cycle is potentially unsafe

The occurrence of two antral follicle recruitment waves in a single inter-ovulatory interval has been detected in ovaries of normal women. This data supports the claim that a double ovarian stimulation in the same cycle may benefit poor responder patients with an increased recovery of mature oocytes and good quality embryos per single cycle. The double stimulation protocol was the object of several published studies in which, surprisingly, the mechanism and the safety of the double stimulation in the same cycle were poorly addressed. We propose that in the double stimulation protocol, the first stimulation impacts more committed oocytes progenitors ready to differentiate into mature oocytes. Conversely, the protracted exposure of developmentally earlier less-committed ovarian stem cells to FSH, which occurs in the double stimulation protocol, impacts the less differentiated stem cells which take longer to differentiate into oocytes. The proposed mechanism has broad implications for the safety of the double stimulation strategy.

DDX4 + stem cells in the ovaries of postmenopausal women: existence and differentiation potential

Ovarian aging is a pacemaker with multiple organ dysfunction. Recently, stem cells with the ability to generate new oocytes have been identified, which provides the possibility of stem cell therapy for ovarian aging. Several studies have revealed the existence of stem cells in human postmenopausal ovary. In this study, we describe a new method using magnetic activated cell sorting combined with differential adhesion to isolate DDX4 + stem cells from ovaries of postmenopausal women and show that the cells exhibit similar gene expression profiles and growth characteristics with primitive germ cells. Furthermore, the DDX4 + stem cells could enter meiosis stage and differentiation into oocytes. The RNA-seq data of the differentiated oocytes shows that mitochondrial metabolism may play an important role in the oogenesis process of the DDX4 + stem cells. Through using human ovarian cortical fragments transplantation model, we indicated that the GFP-DDX4 + stem cells differentiated into some GFP positive oocyte-like structure in vivo. Our study provided a new method for the isolation of DDX4 + stem cells from the ovaries of postmenopausal women and confirmed the ability of these stem cells to differentiate into oocytes.

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

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

Bone marrow-derived mesenchymal stem cells combined with gonadotropin therapy restore postnatal oogenesis of chemo-ablated ovaries in rats via enhancing very small embryonic-like stem cells

BACKGROUND

Very small embryonic-like stem cells (VSELs) are a rare population within the ovarian epithelial surface. They contribute to postnatal oogenesis as they have the ability to generate immature oocytes and resist the chemotherapy. These cells express markers of pluripotent embryonic and primordial germ cells.

OBJECTIVE

We aimed to explore the capability of VSELs in restoring the postnatal oogenesis of chemo-ablated rat ovaries treated with bone marrow-derived mesenchymal stem cells (BM-MSCs) combined with pregnant mare serum gonadotropin (PMSG).

METHODS

Female albino rats were randomly assigned across five groups: I (control), II (chemo-ablation), III (chemo-ablation + PMSG), IV (chemo-ablation + MSCs), and V (chemo-ablation + PMSG + MSCs). Postnatal oogenesis was assessed through measurement of OCT4, OCT4A, Scp3, Mvh, Nobox, Dazl4, Nanog, Sca-1, FSHr, STRA8, Bax, miR143, and miR376a transcript levels using qRT-PCR. Expression of selected key proteins were established as further confirmation of transcript expression changes. Histopathological examination and ovarian hormonal assessment were determined.

RESULTS

Group V displayed significant upregulation of all measured genes when compared with group II, III or IV. Protein expression confirmed the changes in transcript levels as group V displayed the highest average density in all targeted proteins. These results were confirmed histologically by the presence of cuboidal germinal epithelium, numerous primordial, unilaminar, and mature Graafian follicles in group V.

CONCLUSION

VSELs can restore the postnatal oogenesis in chemo-ablated ovaries treated by BM-MSCs combined with PMSG.

Actions and Roles of FSH in Germinative Cells

Follicle stimulating hormone (FSH) is produced by the pituitary gland in a coordinated hypothalamic-pituitary-gonadal (HPG) axis event, plays important roles in reproduction and germ cell development during different phases of reproductive development (fetal, neonatal, puberty, and adult life), and is consequently essential for fertility. FSH is a heterodimeric glycoprotein hormone of two dissociable subunits, α and β. The FSH β-subunit (FSHβ) function starts upon coupling to its specific receptor: follicle-stimulating hormone receptor (FSHR). FSHRs are localized mainly on the surface of target cells on the testis and ovary (granulosa and Sertoli cells) and have recently been found in testicular stem cells and extra-gonadal tissue. Several reproduction disorders are associated with absent or low FSH secretion, with mutation of the FSH β-subunit or the FSH receptor, and/or its signaling pathways. However, the influence of FSH on germ cells is still poorly understood; some studies have suggested that this hormone also plays a determinant role in the self-renewal of germinative cells and acts to increase undifferentiated spermatogonia proliferation. In addition, in vitro, together with other factors, it assists the process of differentiation of primordial germ cells (PGCLCs) into gametes (oocyte-like and SSCLCs). In this review, we describe relevant research on the influence of FSH on spermatogenesis and folliculogenesis, mainly in the germ cell of humans and other species. The possible roles of FSH in germ cell generation in vitro are also presented.

Combined Effect of Anti-SSEA4 and Anti-Globo H Antibodies on Breast Cancer Cells

The globo-series glycosphingolipids (SSEA3, SSEA4, and Globo H) were shown to express in many cancers selectively, and a combination of anti-SSEA4 and anti-Globo H antibodies was able to suppress tumor growth in mice inoculated with breast cancer cell lines. To further understand the effect, we focused on the combined effect of the two antibodies in target binding and antibody-dependent cellular cytotoxicity (ADCC) in vitro. Here, we report that the binding of anti-Globo H antibody (VK9) to MDA-MB231 breast cancer cells was influenced by anti-SSEA4 antibody (MC813-70), and a combination of both antibodies induced a similar effect as did anti-SSEA4 antibodies alone in a reporter-based ADCC assay, indicating that SSEA4 is a major target in breast cancer due to its higher expression than Globo H. Furthermore, we showed that a homogeneous anti-SSEA4 antibody (chMC813-70-SCT) designed to maximize the ADCC activity can be used to isolate a subpopulation of natural killer (NK) cells that exhibit an ∼23% increase in killing the target cells as compared to the unseparated NK cells. These findings can be used to predict a therapy outcome based on the expression levels of antigens and evaluate therapeutic antibody development.

Efficient generation of neural-like cells from porcine ovarian putative stem cells - morphological characterization and evaluation of their electrophysiological properties

Until recently, the mammalian ovary was considered to consist of fully differentiated tissues, but evidence for the presence of adult stem cells in this organ appeared. The differentiation potential of these cells, referred to as putative stem cells, is not well defined. Porcine ovarian putative stem cells (poPSCs) were immunomagnetically isolated from postnatal pig ovaries based on the presence of the SSEA-4 surface marker protein. First, they were cultured in the undifferentiated state. After the third passage, a novel 7-day culture method inducing their differentiation into neural-like cells by the addition of forskolin (FSK), retinoic acid (RA) and basic fibroblast growth factor (bFGF) to the culture medium was applied. After 7 days, poPSCs successfully differentiated into neural-like cells, as evidenced by neural morphology and the presence of the neuronal markers nestin, NeuN, and GFAP, as confirmed by immunofluorescence, western blot, and real-time PCR. Electrophysiological analysis of potassium and sodium channel activity (patch clamp) confirmed that they indeed differentiated into neurons. The plasticity of poPSCs offers an excellent opportunity, especially in the field of neuroscience, since they can differentiate into neurons or glial cells. Although poPSCs might not be pluripotent cells, they also escape the rigid classification framework of adult stem cells.

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

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

Similar Population of CD133+ and DDX4+ VSEL-Like Stem Cells Sorted from Human Embryonic Stem Cell, Ovarian, and Ovarian Cancer Ascites Cell Cultures: The Real Embryonic Stem Cells?

A population of small stem cells with diameters of up to 5 μm resembling very small embryonic-like stem cells (VSELs) were sorted from human embryonic stem cell (hESC) cultures using magnetic-activated cell sorting (MACS) based on the expression of a stem-cell-related marker prominin-1 (CD133). These VSEL-like stem cells had nuclei that almost filled the whole cell volume and expressed stem-cell-related markers (CD133, SSEA-4) and markers of germinal lineage (DDX4/VASA, PRDM14). They were comparable to similar populations of small stem cells sorted from cell cultures of normal ovaries and were the predominant cells in ascites of recurrent ovarian cancer. The sorted populations of CD133+ VSEL-like stem cells were quiescent in vitro, except for ascites, and were highly activated after exposure to valproic acid and follicle-stimulating hormone (FSH), indicating a new tool to study these cells in vitro. These VSEL-like stem cells spontaneously formed clusters resembling tumour-like structures or grew into larger, oocyte-like cells and were differentiated in vitro into adipogenic, osteogenic and neural lineages after sorting. We propose the population of VSEL-like stem cells from hESC cultures as potential original embryonic stem cells, which are present in the human embryo, persist in adult human ovaries from the embryonic period of life and are involved in cancer manifestation.

Functional Testing of Primitive Oocyte-like Cells Developed in Ovarian Surface Epithelium Cell Culture from Small VSEL-like Stem Cells: Can They Be Fertilized One Day?

Data from the literature show that there are different populations of stem cells present in human adult ovaries, including small stem cells resembling very small embryonic-like stem cells (VSELs). These small ovarian stem cells with diameters of up to 5 μm are present in the ovarian surface epithelium and can grow into bigger, primitive oocyte-like cells that express several markers of a germinal lineage and exhibit pluripotency but not the zona pellucida structure when cultured in vitro. In this report, we present the results of the functional testing of such primitive oocyte-like cells from one patient with premature ovarian failure after insemination with her partners' sperm. Knowing that even immature oocytes collected in an in vitro fertilization program cannot be fertilized naturally, we were only interested in determining whether and how these cells react to added sperm and whether spermatozoa somehow "recognize" them. Interestingly, the primitive oocyte-like cells quickly released a zona pellucida-like structure in the presence of sperm. Two different populations of cells were distinguished, those with a thick and those with a thin zona pellucida-like structure. The primitive oocyte-like cells with a released zona pellucida-like structure expressed the pluripotency-related gene OCT4A (POU5F1) and zona pellucida-related gene ZP3, similar to oocytes obtained from in vitro fertilization but not somatic chondrocytes. In a small proportion of these cells, a single-spermatozoon was observed inside the cytoplasm, but no signs of fertilization were found. These observations may suggest a primitive "cortical reaction". Our data further confirm the presence of germinal stem cells in the ovarian surface epithelium cell culture.

Autologous mitochondrial transfer as a complementary technique to intracytoplasmic sperm injection to improve embryo quality in patients undergoing in vitro fertilization-a randomized pilot study

OBJECTIVE

To study if autologous mitochondrial transfer (AUGMENT) improves outcome in patients with previously failed in vitro fertilization (IVF).

DESIGN

Randomized, controlled, triple-blind, experimental study.

SETTING

Private infertility center, Valencian Institute of Infertility (IVI-RMA), Valencia, Spain.

PATIENT(S)

Infertile women ≤42 years of age, body mass index <30 kg/m², antimüllerian hormone ≥4 pmol/L, >5 million/mL motile sperm, at least one previous IVF with at least five metaphase oocytes (MIIs) collected, and low embryo quality.

INTERVENTIONS(S)

An ovarian cortex biopsy was performed to isolate egg precursor cells to obtain their mitochondria. Sibling MIIs were randomly allocated to AUGMENT (experimental) or intracytoplasmic sperm injection (Control). In AUGMENT, mitochondrial suspension was injected along with the sperm. Viable blastocysts from both groups were biopsied for preimplantation genetic testing for aneuploidy.

MAIN OUTCOME MEASURE(S)

Pregnancy, embryo quality.

RESULT(S)

An interim analysis was conducted. The patients' mean age was 36.3 ± 3.6 years, and they had an average of 2.5 ± 1.5 previous IVF cycles. Two of the 59 enrolled patients spontaneously conceived (one miscarried). Fifty-seven patients had ovarian biopsies and underwent stimulation. Oocyte retrieval was performed in 56 patients (premature ovulation; n = 1). A total of 253 MIIs were inseminated in AUGMENT and 250 in Control; fertilization rates were 62.7 ± 30.0% and 68.7 ± 29.1%, respectively. Statistical differences were observed in day 5 blastocyst formation rates (23.3 ± 32.0% vs. 41.1 ± 36.9%). Neither the euploid rate per biopsied blastocyst (43.8 ± 41.7% vs. 63.8 ± 44.1%) nor the euploid rate per MII (9.8 ± 20.5% vs. 11.9 ± 16.1%) between AUGMENT and Control achieved statistical significance. Moreover, no differences were seen regarding mitochondrial DNA content and relevant morphokinetic variables. Thirty patients were able to undergo embryo transfer. Cumulative live birth rates per transferred embryo were 41.6% in AUGMENT and 41.2% in Control.

CONCLUSION(S)

AUGMENT does not seem to improve prognosis in this population. Therefore, the study has been discontinued.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02586298.

Carbohydrate Targets for CAR T Cells in Solid Childhood Cancers

Application of the CAR targeting strategy in solid tumors is challenged by the need for adequate target antigens. As a consequence of their tissue origin, embryonal cancers can aberrantly express membrane-anchored gangliosides. These are carbohydrate molecules consisting of a glycosphingolipid linked to sialic acids residues. The best-known example is the abundant expression of ganglioside G_D2 on the cell surface of neuroblastomas which derive from G_D2-positive neuroectoderm. Gangliosides are involved in various cellular functions, including signal transduction, cell proliferation, differentiation, adhesion and cell death. In addition, transformation of human cells to cancer cells can be associated with distinct glycosylation profiles which provide advantages for tumor growth and dissemination and can serve as immune targets. Both gangliosides and aberrant glycosylation of proteins escape the direct molecular and proteomic screening strategies currently applied to identify further immune targets in cancers. Due to their highly restricted expression and their functional roles in the malignant behavior, they are attractive targets for immune engineering strategies. G_D2-redirected CAR T cells have shown activity in clinical phase I/II trials in neuroblastoma and next-generation studies are ongoing. Further carbohydrate targets for CAR T cells in preclinical development are O-acetyl-G_D2, NeuGc-GM3 (N-glycolyl GM3), G_D3, SSEA-4, and oncofetal glycosylation variants. This review summarizes knowledge on the role and function of some membrane-expressed non-protein antigens, including gangliosides and abnormal protein glycosylation patterns, and discusses their potential to serve as a CAR targets in pediatric solid cancers.

Characterization of stem cell and cancer stem cell populations in ovary and ovarian tumors

Background

Ovarian cancer is a complicated malady associated with cancer stem cells (CSCs) contributing to 238,700 estimated new cases and 151,900 deaths per year, worldwide. CSCs comprise a tiny fraction of tumor-bulk responsible for cancer recurrence and eventual mortality. CSCs or tumor initiating cells are responsible for self-renewal, differentiation and proliferative potential, tumor initiation capability, its progression, drug resistance and metastatic spread. Although several biomarkers are implicated in these processes, their distribution within the ovary and association with single cell type has neither been established nor demonstrated across ovarian tumor developmental stages. Therefore, precise identification, thorough characterization and effective targeted destruction of dormant and highly proliferating potent CSC populations is an immediate need.

Results

In view of this, distribution of various CSC (ALDH1/2, C-KIT, CD133, CD24 and CD44) and cell proliferation (KI67) specific markers in the ovarian surface epithelium (OSE) and cortex regions in normal ovary, and benign, borderline and high grade metastatic ovarian tumors by immuno-histochemistry and confocal microscopy was studied. We further confirmed their expression by RT-PCR analysis. Co-expression analysis of stem cell (OCT4, SSEA4) and CSC (ALDH1/2, CD44 and LGR5) markers with proliferation marker (KI67) in HG tumors revealed dual positive proliferating stem and CSCs, few non-proliferating stem/CSC (SSEA4⁺/KI67⁻ and ALDH1/2⁺/KI67⁻) and only KI67⁺ cells in cortex, signifying dynamic populations and interesting cellular hierarchy in cortex region. Smaller spherical (≤ 5 μm) and larger spindle/elliptical shaped (~ 10 μm) cell populations with high nucleo-cytoplasmic ratio were detected across all samples (including normal ovaries) but with variable distribution and characteristic stage-wise marker expression across different tumor stages.

Conclusions

Diverse stem and CSC populations expressing characteristic markers revealing distinct phenotypes (spherical ≤5 μm and spindle/elliptical ~ 10 μm) were distributed within different tumor stages studied signifying dynamic and probable functional hierarchy within these cell types. Involvement of extra-ovarian sites of origin of stem and CSCs requires rigorous evaluation. Quantitative analysis of potent CSC populations, their mechanisms and pathways for self-renewal, chemo-resistance, metastatic spread etc. with respect to various markers studied, will provide better insights and targets for developing effective therapeutics to prevent metastasis and eventually help improve patient mortality.

Electronic supplementary material

The online version of this article (10.1186/s13048-018-0439-3) contains supplementary material, which is available to authorized users.

In situ characterization of stem cells-like biomarkers in meningiomas

Background

Meningioma cancer stem cells (MCSCs) contribute to tumor aggressiveness and drug resistance. Successful therapies developed for inoperable, recurrent, or metastatic tumors must target these cells and restrict their contribution to tumor progression. Unfortunately, the identity of MCSCs remains elusive, and MSCSs’ in situ spatial distribution, heterogeneity, and relationship with tumor grade, remain unclear.

Methods

Seven tumors classified as grade II or grade III, including one case of metastatic grade III, and eight grade I meningioma tumors, were analyzed for combinations of ten stem cell (SC)-related markers using immunofluorescence of consecutive sections. The correlation of expression for all markers were investigated. Three dimensional spatial distribution of markers were qualitatively analyzed using a grid, designed as a repository of information for positive staining. All statistical analyses were completed using Statistical Analysis Software Package.

Results

The patterns of expression for SC-related markers were determined in the context of two dimensional distribution and cellular features. All markers could be detected in all tumors, however, Frizzled 9 and GFAP had differential expression in grade II/III compared with grade I meningioma tissues. Correlation analysis showed significant relationships between the expression of GFAP and CD133 as well as SSEA4 and Vimentin. Data from three dimensional analysis showed a complex distribution of SC markers, with increased gene hetero-expression being associated with grade II/III tumors. Sub regions that showed multiple co-staining of markers including CD133, Frizzled 9, GFAP, Vimentin, and SSEA4, but not necessarily the proliferation marker Ki67, were highly associated with grade II/III meningiomas.

Conclusion

The distribution and level of expression of CSCs markers in meningiomas are variable and show hetero-expression patterns that have a complex spatial nature, particularly in grade II/III meningiomas. Thus, results strongly support the notion of heterogeneous populations of CSCs, even in grade I meningiomas, and call for the use of multiple markers for the accurate identification of individual CSC subgroups. Such identification will lead to practical clinical diagnostic protocols that can quantitate CSCs, predict tumor recurrence, assist in guiding treatment selection for inoperable tumors, and improve follow up of therapy.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0571-6) contains supplementary material, which is available to authorized users.

Ovarian Cancer Stem Cells: Unraveling a Germline Connection

Ovarian cancer is most lethal among gynecological cancers with often fatal consequences due to lack of effective biomarkers and relapse, which propels ovarian cancer research into unique directions to establish solid targeted therapeutics. "Ovarian stem cells" expressing germline pluripotent markers serve as novel paradigm with potential to address infertility, menopause, and probably influence tumor initiation. Cancer stem cells (CSCs) pose vital role in tumor recurrence and hence it is extremely important to study them with respect to ovarian stem cells across various cancer stages and normal ovaries. Pluripotent (OCT4, NANOG, SOX2, SSEA1, and SSEA4), germline (IFITM3, VASA/DDX4), and cancer stem (CD44, LGR5) cell specific markers were characterized for protein and mRNA expression in tumor tissues to understand their distribution in the surface epithelium and ovarian cortex in benign, borderline, and high-grade malignant stages. To elucidate whether pluripotent ovarian germline stem cells and CSCs are common subset of stem cells in tumor tissues, VASA was colocalized with known pluripotent stem (OCT4, SSEA1, SSEA4) and CSC (CD44, LGR5) specific markers by confocal microscopy. Single, smaller spherical (≤5 μm), and larger elliptical fibroblast like (≥10 μm) cells (also in clusters or multiples) were detected implying probable functional behavioral significance of cells in tumor initiation and metastasis across various cancer stages. Cells revealed characteristic staining pattern in ovarian surface epithelium (OSE) and cortex regions exclusive for each marker. Co-expression studies revealed specific subpopulations existing simultaneously in OSE and cortex and that a dynamic hierarchy of (cancer) stem cells with germline properties prevails in normal ovaries and cancer stages. Novel insights into CSC biology with respect to ovarian and germline stem cell perspective were obtained. Understanding molecular signatures and distribution within ovarian tissue may enable identification of precise tumor-initiating CSC populations and signaling pathways thus improving their efficient targeting and strategies to prevent their dissemination causing fatal relapse.

Improved Isolation, Proliferation, and Differentiation Capacity of Mouse Ovarian Putative Stem Cells

The recent discovery of ovarian stem cells in postnatal mammalian ovaries, also referred to as putative stem cells (PSCs), and their roles in mammalian fertility has challenged the long-existing theory that women are endowed with a certain number of germ cells. The rare amount of PSCs is the major limitation for utilizing them through different applications. Therefore, this study was conducted in six phases to find a way to increase the number of Fragilis- and mouse vasa homolog (MVH)-positive sorted cells from 14-day-old NMRI strain mice. Results showed that there is a population of Fragilis- and MVH-positive cells with pluripotent stem cell characteristics, which can be isolated and expanded for months in vitro. PSCs increase their proliferation capacity under the influence of some mitogenic agents, and our results showed that different doses of stem cell factor (SCF) induce PSC proliferation with the maximum increase observed at 50 ng/mL. SCF was also able to increase the number of Fragilis- and MVH-positive cells after sorting by magnetic-activated cell sorting and enhance colony formation efficiency in sorted cells. Differentiation capacity assay indicated that there is a basic level of spontaneous differentiation toward oocyte-like cells during 3 days of culture. However, relative gene expression was significantly higher in the follicle-stimulating hormone-treated groups, especially in the Fragilis- sorted PSCs. We suggest that higher number of PSCs provides us either a greater source of energy that can be injected into energy-impaired oocytes in women with a history of repeat IVF failure or a good source for research.

Neo-oogenesis in mammals

Recently, the existence of a mechanism for neo-oogenesis in the ovaries of adult mammals has generated much controversy within reproductive biology. This mechanism, which proposes that the ovary has cells capable of renewing the follicular reserve, has been described for various species of mammals. The first evidence was found in prosimians and humans. However, these findings were not considered relevant because the predominant dogma for reproductive biology at the time was that of Zuckerman. This dogma states that female mammals are born with finite numbers of oocytes that decline throughout postnatal life. Currently, the concept of neo-oogenesis has gained momentum due to the discovery of cells with mitotic activity in adult ovaries of various mammalian species (mice, humans, rhesus monkeys, domestic animals such as pigs, and wild animals such as bats). Despite these reports, the concept of neo-oogenesis has not been widely accepted by the scientific community, generating much criticism and speculation about its accuracy because it has been impossible to reproduce some evidence. This controversy has led to the creation of two positions: one in favour of neo-oogenesis and the other against it. Various animal models have been used in support of both camps, including both classic laboratory animals and domestic and wild animals. The aim of this review is to critically present the current literature on the subject and to evaluate the arguments pro and contra neo-oogenesis in mammals.

Putative stem cells and epithelial-mesenchymal transition revealed in sections of ovarian tumor in patients with serous ovarian carcinoma using immunohistochemistry for vimentin and pluripotency-related markers

Background

The mechanism of aggressive character of ovarian cancer and unsuccessful treatment of women with this deadly disease has been recently explained by the theory of cancer stem cells (CSCs). It has been reported that ovarian carcinogenesis and progression of disease is associated with epithelial-mesenchymal transition (EMT). EMT, a physiological cell process during embryonic development and later in life during regeneration, could, when induced in pathological condition, generate CSCs-like cells. Until now EMT in the ovarian tissue has been mainly studied in cell cultures in vitro. The aim of this study was to focus on in situ morphological changes in the ovarian surface epithelium of tumor tissue in women with epithelial ovarian cancer after we applied the antibodies for markers of EMT vimentin and pluripotency-related markers NANOG, SOX2 and SSEA-4.

Methods

We analyzed ovarian tissue sections of 20 women with high grade serous ovarian carcinoma. After eosin and hematoxylin staining, used in standard practice, immunohistochemistry was performed for vimentin and markers of pluripotency: NANOG, SSEA-4 and SOX2. We focused on the ovarian surface epithelium in order to observe morphological changes in tumor tissue.

Results

Among epithelial cells of the ovarian surface epithelium in women with serous ovarian carcinoma we observed a population of small NANOG-positive cells with diameters of up to 5 μm and nuclei, which filled almost the entire cell volumes. These small NANOG-positive cells were in some cases concentrated in the regions with morphologically changed epithelial cells. In these regions, a population of bigger round cells with diameters of 10–15 μm with large nuclei, and positively stained for vimentin, NANOG and other markers of pluripotnecy, were released from the surface epithelium. These cells are proposed as CSCs, and possibly originate from small stem cells among epithelial cells. They formed typical cell clusters, invaded the tissue by changing their round shape into a mesenchymal-like phenotype, and contributed to the manifestation of ovarian cancer.

Conclusions

Our findings show morphological changes in the ovarian surface epithelium in tumor slides of high grade serous ovarian carcinoma and provide a new population of putative CSCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-017-0306-7) contains supplementary material, which is available to authorized users.

Used protocols for isolation and propagation of ovarian stem cells, different cells with different traits

Although existence of ovarian stem cells (OSCs) in mammalian postnatal ovary is still under controversy, however, it has been almost accepted that OSCs are contributing actively to folliculogenesis and neo-oogenesis. Recently, various methods with different efficacies have been employed for OSCs isolation from ovarian tissue, which these methods could be chosen depends on aim of isolation and accessible equipments and materials in lab. Although isolated OSCs from different methods have various traits and characterizations, which might become from their different nature and origin, however these stem cells are promising source for woman infertility treatment or source of energy for women with a history of repeat IVF failure in near future. This review has brought together and summarized currently used protocols for isolation and propagation of OSCs in vitro.

Novel population of small tumour-initiating stem cells in the ovaries of women with borderline ovarian cancer

Small stem cells with diameters of up to 5 μm previously isolated from adult human ovaries indicated pluripotency and germinal lineage, especially primordial germ cells, and developed into primitive oocyte-like cells in vitro. Here, we show that a comparable population of small stem cells can be found in the ovarian tissue of women with borderline ovarian cancer, which, in contrast to small stem cells in "healthy" ovaries, formed spontaneous tumour-like structures and expressed some markers related to pluripotency and germinal lineage. The gene expression profile of these small putative cancer stem cells differed from similar cells sorted from "healthy" ovaries by 132 upregulated and 97 downregulated genes, including some important forkhead box and homeobox genes related to transcription regulation, developmental processes, embryogenesis, and ovarian cancer. These putative cancer stem cells are suggested to be a novel population of ovarian tumour-initiating cells in humans.

Endogenous, very small embryonic-like stem cells: critical review, therapeutic potential and a look ahead

BACKGROUND

Both pluripotent very small embryonic-like stem cells (VSELs) and induced pluripotent stem (iPS) cells were reported in 2006. In 2012, a Nobel Prize was awarded for iPS technology whereas even today the very existence of VSELs is not well accepted. The underlying reason is that VSELs exist in low numbers, remain dormant under homeostatic conditions, are very small in size and do not pellet down at 250-280g. The VSELs maintain life-long tissue homeostasis, serve as a backup pool for adult stem cells and are mobilized under stress conditions. An imbalance in VSELs function (uncontrolled proliferation) may result in cancer.

SEARCH METHODS

The electronic database 'Medline/Pubmed' was systematically searched with the subject heading term 'very small embryonic-like stem cells'.

OBJECTIVE AND RATIONALE

The most primitive stem cells that undergo asymmetric cell divisions to self-renew and give rise to progenitors still remain elusive in the hematopoietic system and testes, while the presence of stem cells in ovary is still being debated. We propose to review the available literature on VSELs, the methods of their isolation and characterization, their ontogeny, how they compare with embryonic stem (ES) cells, primordial germ cells (PGCs) and iPS cells, and their role in maintaining tissue homeostasis. The review includes a look ahead on how VSELs will result in paradigm shifts in basic reproductive biology.

OUTCOMES

Adult tissue-specific stem cells including hematopoietic, spermatogonial, ovarian and mesenchymal stem cells have good proliferation potential and are indeed committed progenitors (with cytoplasmic OCT-4), which arise by asymmetric cell divisions of pluripotent VSELs (with nuclear OCT-4). VSELs are the most primitive stem cells and postulated to be an overlapping population with the PGCs. Rather than migrating only to the gonads, PGCs migrate and survive in various adult body organs throughout life as VSELs. VSELs express both pluripotent and PGC-specific markers and are epigenetically and developmentally more mature compared with ES cells obtained from the inner cell mass of a blastocyst-stage embryo. As a result, VSELs readily differentiate into three embryonic germ layers and spontaneously give rise to both sperm and oocytes in vitro. Like PGCs, VSELs do not divide readily in culture, nor produce teratoma or integrate in the developing embryo. But this property of being relatively quiescent allows endogenous VSELs to survive various kinds of toxic insults. VSELs that survive oncotherapy can be targeted to induce endogenous regeneration of non-functional gonads. Transplanting healthy niche (mesenchymal) cells have resulted in improved gonadal function and live births.

WIDER IMPLICATIONS

Being quiescent, VSELs possibly do not accumulate genomic (nuclear or mitochondrial) mutations and thus may be ideal endogenous, pluripotent stem cell candidates for regenerative and reproductive medicine. The presence of VSELs in adult gonads and the fact that they survive oncotherapy may obviate the need to bank gonadal tissue for fertility preservation prior to oncotherapy. VSELs and their ability to undergo spermatogenesis/neo-oogenesis in the presence of a healthy niche will help identify newer strategies toward fertility restoration in cancer survivors, delaying menopause and also enabling aged mothers to have better quality eggs.

Small putative NANOG, SOX2, and SSEA-4-positive stem cells resembling very small embryonic-like stem cells in sections of ovarian tissue in patients with ovarian cancer

BACKGROUND

In previous studies it has been found that in cell cultures of human adult ovaries there is a population of small stem cells with diameters of 2-4 μm, which are present mainly in the ovarian surface epithelium and are comparable to very small embryonic-like stem cells (VSELs) from bone marrow. These cells are not observed by histopathologists in the ovarian tissue due to their small size and unknown clinical significance. Because these cells express a degree of pluripotency, they might be involved in the manifestation of ovarian cancer. Therefore we studied the ovarian tissue sections in women with borderline ovarian cancer and serous ovarian carcinoma to perhaps identify the small putative stem cells in situ.

METHODS

In 27 women with borderline ovarian cancer and 20 women with high-grade serous ovarian carcinoma the ovarian tissue sections were stained, per standard practice, with eosin and hematoxylin staining and on NANOG, SSEA-4 and SOX2 markers, related to pluripotency, using immunohistochemistry. We focused on the presence and localization of small putative stem cells with diameters of up to 5 μm and with the nuclei spread over nearly the full cell volume.

RESULTS

In ovarian sections of both borderline ovarian cancer and serous ovarian carcinoma patients we were able to identify the presence of small round cells complying with the above criteria. Some of these small cells were NANOG-positive, were located among epithelial cells in the ovarian surface epithelium and as a single cell or groups of cells/clusters in typical "chambers", were found only in the presence of ovarian cancer and not in healthy ovaries and are comparable to those in fetal ovaries. We envision that these small cells could be related to NANOG-positive tumor-like structures and oocyte-like cells in similar "chambers" found in sections of cancerous ovaries, which could support their stemness and pluripotency. Further immunohistochemistry revealed a similar population of SSEA-4 and SOX2-positive cells.

CONCLUSIONS

We may conclude that putative small stem cells expressing markers, related to pluripotency, are present in the ovarian tissue sections of women with borderline ovarian cancer and high-grade serous ovarian carcinoma thus indicating their potential involvement in ovarian cancer.

Very Small Embryonic-Like Stem Cells: A Potential Developmental Link Between Germinal Lineage and Hematopoiesis in Humans

It has been suggested that hematopoietic stem/progenitor cells (HSPCs) could become specified from a population of migrating primordial germ cells (PGCs), precursors of gametes, during embryogenesis. Some recent experimental data demonstrated that the cell population that is usually considered to be PGCs, moving toward the gonadal ridges of an embryo, contains a subset of cells coexpressing several germ cell and hematopoietic markers and possessing hematopoietic activity. Experimental data showed that bone morphogenetic protein 4 (BMP4) generates PGCs from mouse bone marrow-derived pluripotent stem cells. Interestingly, functional reproductive hormone receptors have been identified in HSPCs, thus indicating their potential role in reproductive function. Several reports have demonstrated fertility restoration and germ cell generation after bone marrow transplantation in both animal models and humans. A potential link between HSPCs and germinal lineage might be represented by very small embryonic-like stem cells (VSELs), which have been found in adult human bone marrow, peripheral blood, and umbilical cord blood, express a specific pattern of pluripotency, germinal lineage, and hematopoiesis, and are proposed to persist in adult tissues and organs from the embryonic period of life. Stem cell populations, similar to VSELs, expressing several genes related to pluripotency and germinal lineage, especially to PGCs, have been discovered in adult human reproductive organs, ovaries and testicles, and were related to primitive germ cell-like cell development in vitro, thus supporting the idea of VSELs as a potential link between germinal lineage and hematopoiesis.

Identification of New Rat Bone Marrow-Derived Population of Very Small Stem Cell with Oct-4A and Nanog Expression by Flow Cytometric Platforms

Very small embryonic-like stem cells (VSELs) represent a unique rare population of adult stem cells (SCs) sharing several structural, genetic, biochemical, and functional properties with embryonic SCs and have been identified in several adult murine and human tissues. However, rat bone marrow- (BM-) derived SCs closely resembling murine or human VSELs have not been described. Thus, we employed multi-instrumental flow cytometric approach including classical and imaging cytometry and we established that newly identified population of nonhematopoietic cells expressing CD106 (VCAM-I) antigen contains SCs with very small size, expressing markers of pluripotency (Oct-4A and Nanog) on both mRNA and protein levels that indicate VSEL population. Based on our experience in both murine and human VSEL isolation procedures by fluorescence-activated cell sorting (FACS), we also optimized sorting protocol for separation of CD45⁻/Lin⁻/CD106⁺ rat BM-derived VSELs from wild type and eGFP-expressing rats, which are often used as donor animals for cell transplantations in regenerative studies in vivo. Thus, this is a first study identifying multiantigenic phenotype and providing sorting protocols for isolation VSELs from rat BM tissue for further examining of their functional properties in vitro as well as regenerative capacity in distinct in vivo rat models of tissue injury.

Improvement in Isolation and Identification of Mouse Oogonial Stem Cells

Female germline stem cells (FGSCs) or oogonial stem cells (OSCs) have the capacity to generate newborn oocytes and thus open a new door to fight ovarian aging and female infertility. However, the production and identification of OSCs are difficult for investigators. Rare amount of these cells in the ovary results in the failure of the acquisition of OSCs. Furthermore, the oocyte formation by OSCs in vivo was usually confirmed using tissue sections by immunofluorescence or immunohistochemistry in previous studies. STO or MEF feeder cells are derived from mouse, not human. In our study, we modified the protocol. The cells were digested from ovaries and cultured for 2-3 days and then were purified by magnetic-activated cell sorting (MACS). The ovaries and fetus of mice injected with EGFP-positive OSCs were prepared and put on the slides to directly visualize oocyte and progeny formation under microscope. Additionally, the human umbilical cord mesenchymal stem cells (hUC-MSCs) were also used as feeder cells to support the proliferation of OSCs. The results showed that all the modified procedures can significantly improve and facilitate the generation and characterization of OSCs, and hUC-MSCs as feeder will be useful for isolation and proliferation of human OSCs avoiding contamination from mouse.

Novel Action of FSH on Stem Cells in Adult Mammalian Ovary Induces Postnatal Oogenesis and Primordial Follicle Assembly

Adult mammalian ovary has been under the scanner for more than a decade now since it was proposed to harbor stem cells that undergo postnatal oogenesis during reproductive period like spermatogenesis in testis. Stem cells are located in the ovary surface epithelium and exist in adult and menopausal ovary as well as in ovary with premature failure. Stem cells comprise two distinct populations including spherical, very small embryonic-like stem cells (VSELs which express nuclear OCT-4 and other pluripotent and primordial germ cells specific markers) and slightly bigger ovarian germ stem cells (OGSCs with cytoplasmic OCT-4 which are equivalent to spermatogonial stem cells in the testes). These stem cells have the ability to spontaneously differentiate into oocyte-like structures in vitro and on exposure to a younger healthy niche. Bone marrow may be an alternative source of these stem cells. The stem cells express FSHR and respond to FSH by undergoing self-renewal, clonal expansion, and initiating neo-oogenesis and primordial follicle assembly. VSELs are relatively quiescent and were recently reported to survive chemotherapy and initiate oogenesis in mice when exposed to FSH. This emerging understanding and further research in the field will help evolving novel strategies to manage ovarian pathologies and also towards oncofertility.

CD90 and CD105 expression in the mouse ovary and testis at different stages of postnatal development

CD90 (i.e., THY1) and CD105 (i.e., endoglin) are glycoproteins known as mesenchymal stem cell markers that are expressed in various cell types including male and female gonadal cells. We aimed to determine ovarian and testicular expression of CD90 and CD105 in various cell types during postnatal development in mice. The present study was carried out on male (C57BL/6) and female (Balb/C) mice during critical stages of gonadal development. Immunohistochemical localization of CD90 and CD105 was determined in the ovaries obtained at postnatal days (PND) -1, -7, -21 and -60 and in the testes obtained at PND6, -8, -16, -20, -29, -32 and -88. The relative expression of CD90 and CD105 was evaluated by ImageJ software and data were analyzed by analysis of variance. The relative expression of CD90 and CD105 varied during postnatal development and increased significantly in the adult ovary (PND60) and testis (PND88) compared to the early postnatal gonads. In the ovaries, the expression of CD90 was significantly higher in somatic cells in comparison to germ cell compartments. In the testis, CD90 expression was greater in germ cells and Sertoli cells compared to other cell types. Expression of CD105 was higher in germ cells than somatic cells of both the ovary and testis. In addition to different expression of CD90 and CD105 during various developmental stages, also their altered expression in particular cell types suggests specific roles of these glycoproteins in physiological processes of mouse gonads.

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.

Expression of stage-specific embryonic antigen-4 (SSEA-4) defines spontaneous loss of epithelial phenotype in human solid tumor cells

Stage-specific embryonic antigen-4 (SSEA-4) is a glycosphingolipid, which is overexpressed in some cancers and has been linked to disease progression. However, little is known about the functions of SSEA-4 and the characteristics of SSEA-4 expressing tumor cells. Our studies identified SSEA-4 expression on a subpopulation of cells in many solid tumor cell lines but not in leukemic cell lines. Fluorescence-activated cell sorting-sorted SSEA-4(+) prostate cancer cells formed fibroblast-like colonies with limited cell-cell contacts, whereas SSEA-4(-) cells formed cobblestone-like epithelial colonies. Only colonies derived from SSEA-4(+) cells were enriched for pluripotent embryonic stem cell markers. Moreover, major epithelial cell-associated markers Claudin-7, E-cadherin, ESRP1 and GRHL2 were down-regulated in the SSEA-4(+) fraction of DU145 and HCT-116 cells. Similar to cell lines, SSEA-4(+) primary prostate tumor cells also showed down-regulation of epithelial cell-associated markers. In addition, they showed up-regulation of epithelial-to-mesenchymal transition as well as mesenchymal markers. Furthermore, SSEA-4(+) cells escape from adhesive colonies spontaneously and form invadopodia-like migratory structures, in which SSEA-4, cortactin as well as active pPI3K, pAkt and pSrc are enriched and colocalized. Finally, SSEA-4(+) cells displayed strong tumorigenic ability and stable knockdown of SSEA-4 synthesis resulted in decreased cellular adhesion to different extracellular matrices. In conclusion, we introduce SSEA-4 as a novel marker to identify heterogeneous, invasive subpopulations of tumor cells. Moreover, increased cell-surface SSEA-4 expression is associated with the loss of cell-cell interactions and the gain of a migratory phenotype, suggesting an important role of SSEA-4 in cancer invasion by influencing cellular adhesion to the extracellular matrix.

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.

Identification and characterization of epithelial cells derived from human ovarian follicular fluid

Introduction

Follicular fluid is important for follicular development and oocyte maturation. Evidence suggests that follicular fluid is not only rich in proteins but cells. Besides oocytes, the follicular fluid contains granulosa, thecal, and ovarian surface epithelial cells, and both granulosa and thecal cells are well-characterized. However, epithelial cells in follicular fluid are poorly studied. This study aims to isolate and characterize in vitro epithelial cells that originate from human ovarian follicular fluid retrieved in the assisted fertilization program.

Methods

Follicular fluid samples were collected from 20 women in the assisted reproduction program. Epithelial cells were characterized by flow cytometry assay, immunofluorescence staining, real-time PCR, and time lapse photography.

Results

Epithelial cell cultures were established from 18 samples. A small population of epithelial cells expresses germ-line stem cell markers, such as octamer-binding transcription factor 4 (OCT4), NANOG, and DEAD box polypeptide 4 (DDX4). In the epithelial cell culture system, oocyte-like cells formed spontaneously in vitro and expressed the following transcription markers: deleted in azoospermia-like (DAZL), developmental pluripotency associated protein 3 stella-related protein (STELLA), zona pellucida gene family C (ZPC), Syntaptonemal complex protein (SCP), and growth and differentiation factor 9 (GDF9). Some of the oocyte-like cells developed a zona pellucida-like structure. Both the symmetric and asymmetric division split of epithelial cells and early developing oocytes were observed using time lapse photography. Cell colonies were formed during epithelial culturing, which maintained and proliferated in an undifferentiated way on the feeder layer and expressed some pluripotency markers. These colonies differentiated in vitro into various somatic cell types in all three germ layers, but did not form teratoma when injected into immunodeficient mice. Furthermore, these epithelial cells could be differentiated directly to functional hepatocyte-like cells, which do not exist in ovarian tissues.

Conclusions

The epithelial cells derived from follicular fluid are a potential stem cell source with a pluripotent/multipotent character for safe application in oogenesis and regenerative medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0004-6) contains supplementary material, which is available to authorized users.

Stem cells, progenitor cells, and lineage decisions in the ovary

Exploring stem cells in the mammalian ovary has unleashed a Pandora's box of new insights and questions. Recent evidence supports the existence of stem cells of a number of the different cell types within the ovary. The evidence for a stem cell model producing mural granulosa cells and cumulus cells is strong, despite a limited number of reports. The recent identification of a precursor granulosa cell, the gonadal ridge epithelial-like cell, is exciting and novel. The identification of female germline (oogonial) stem cells is still very new and is currently limited to just a few species. Their origins and physiological roles, if any, are unknown, and their potential to produce oocytes and contribute to follicle formation in vivo lacks robust evidence. The precursor of thecal cells remains elusive, and more compelling data are needed. Similarly, claims of very small embryonic-like cells are also preliminary. Surface epithelial cells originating from gonadal ridge epithelial-like cells and from the mesonephric epithelium at the hilum of the ovary have also been proposed. Another important issue is the role of the stroma in guiding the formation of the ovary, ovigerous cords, follicles, and surface epithelium. Immune cells may also play key roles in developmental patterning, given their critical roles in corpora lutea formation and regression. Thus, while the cellular biology of the ovary is extremely important for its major endocrine and fertility roles, there is much still to be discovered. This review draws together the current evidence and perspectives on this topic.

Application of a novel population of multipotent stem cells derived from skin fibroblasts as donor cells in bovine SCNT

Undifferentiated stem cells are better donor cells for somatic cell nuclear transfer (SCNT), resulting in more offspring than more differentiated cells. While various stem cell populations have been confirmed to exist in the skin, progress has been restricted due to the lack of a suitable marker for their prospective isolation. To address this fundamental issue, a marker is required that could unambiguously prove the differentiation state of the donor cells. We therefore utilized magnetic activated cell sorting (MACS) to separate a homogeneous population of small SSEA-4⁺ cells from a heterogeneous population of bovine embryonic skin fibroblasts (BEF). SSEA-4⁺ cells were 8-10 μm in diameter and positive for alkaline phosphatase (AP). The percentage of SSEA-4⁺ cells within the cultured BEF population was low (2-3%). Immunocytochemistry and PCR analyses revealed that SSEA-4⁺ cells expressed pluripotency-related markers, and could differentiate into cells comprising all three germ layers in vitro. They remained undifferentiated over 20 passages in suspension culture. In addition, cloned embryos derived from SSEA-4 cells showed significant differences in cleavage rate and blastocyst development when compared with those from BEF and SSEA-4⁻ cells. Moreover, blastocysts derived from SSEA-4⁺ cells showed a higher total cell number and lower apoptotic index as compared to BEF and SSEA-4^– derived cells. It is well known that nuclei from pluripotent stem cells yield a higher cloning efficiency than those from adult somatic cells, however, pluripotent stem cells are relatively difficult to obtain from bovine. The SSEA-4⁺ cells described in the current study provide an attractive candidate for SCNT and a promising platform for the generation of transgenic cattle.

The impact of mitochondrial function/dysfunction on IVF and new treatment possibilities for infertility

Mitochondria play vital roles in oocyte functions and they are critical indicators of oocyte quality which is important for fertilization and development into viable offspring. Quality-compromised oocytes are correlated with infertility, developmental disorders, reduced blastocyst cell number and embryo loss in which mitochondrial dysfunctions play a significant role. Increasingly, women affected by metabolic disorders such as diabetes or obesity and oocyte aging are seeking treatment in IVF clinics to overcome the effects of adverse metabolic conditions on mitochondrial functions and new treatments have become available to restore oocyte quality. The past decade has seen enormous advances in potential therapies to restore oocyte quality and includes dietary components and transfer of mitochondria from cells with mitochondrial integrity into mitochondria-impaired oocytes. New technologies have opened up new possibilities for therapeutic advances which will increase the success rates for IVF of oocytes from women with compromised oocyte quality.

Ovarian germline stem cells

It has long been established that germline stem cells (GSCs) are responsible for lifelong gametogenesis in males, and some female invertebrates (for example, Drosophila) and lower vertebrates (for example, teleost fish and some prosimians) also appear to rely on GSCs to replenish their oocyte reserve in adulthood. However, the presence of such cells in the majority of female mammals is controversial, and the idea of a fixed ovarian reserve determined at birth is the prevailing belief among reproductive biologists. However, accumulating evidence demonstrates the isolation and culture of putative GSCs from the ovaries of adult mice and humans. Live offspring have been reportedly produced from the culture of adult mouse GSCs, and human GSCs formed primordial follicles using a mouse xenograft model. If GSCs were present in adult female ovaries, it could be postulated that the occurrence of menopause is not due to the exhaustion of a fixed supply of oocytes but instead is a result of GSC and somatic cell aging. Alternatively, they may be benign under normal physiological conditions. If their existence were confirmed, female GSCs could have many potential applications in both basic science and clinical therapies. GSCs not only may provide a valuable model for germ cell development and maturation but may have a role in the field of fertility preservation, with women potentially being able to store GSCs or GSC-derived oocytes from their own ovaries prior to infertility-inducing treatments. Essential future work in this field will include further independent corroboration of the existence of GSCs in female mammals and the demonstration of the production of mature competent oocytes from GSCs cultured entirely in vitro.

Identification and characterization of putative stem cells in the adult pig ovary

Recently, the concept of ‘neo-oogenesis’ has received increasing attention, since it was shown that adult mammals have a renewable source of eggs. The purpose of this study was to elucidate the origin of these eggs and to confirm whether neo-oogenesis continues throughout life in the ovaries of the adult mammal. Adult female pigs were utilized to isolate, identify and characterize, including their proliferation and differentiation capabilities, putative stem cells (PSCs) from the ovary. PSCs were found to comprise a heterogeneous population based on c-kit expression and cell size, and also express stem and germ cell markers. Analysis of PSC molecular progression during establishment showed that these cells undergo cytoplasmic-to-nuclear translocation of Oct4 in a manner reminiscent of gonadal primordial germ cells (PGCs). Hence, cells with the characteristics of early PGCs are present or are generated in the adult pig ovary. Furthermore, the in vitro establishment of porcine PSCs required the presence of ovarian cell-derived extracellular regulatory factors, which are also likely to direct stem cell niche interactions in vivo. In conclusion, the present work supports a crucial role for c-kit and kit ligand/stem cell factor in stimulating the growth, proliferation and nuclear reprogramming of porcine PSCs, and further suggests that porcine PSCs might be the culture equivalent of early PGCs.

The proper criteria for identification and sorting of very small embryonic-like stem cells, and some nomenclature issues

Evidence has accumulated that both murine and human adult tissues contain early-development stem cells with a broader differentiation potential than other adult monopotent stem cells. These cells, being pluripotent or multipotent, exist at different levels of specification and most likely represent overlapping populations of cells that, depending on the isolation strategy, ex vivo expansion protocol, and markers employed for their identification, have been given different names. In this review, we will discuss a population of very small embryonic-like stem cells (VSELs) in the context of other stem cells that express pluripotent/multipotent markers isolated from adult tissues as well as review the most current, validated working criteria on how to properly identify and isolate these very rare cells. VSELs have been successfully purified in several laboratories; however, a few have failed to isolate them, which has raised some unnecessary controversy in the field. Therefore, in this short review, we will address the most important reasons that some investigators have experienced problems in isolating these very rare cells and discuss some still unresolved challenges which should be overcome before these cells can be widely employed in the clinic.

Post-natal oogenesis: a concept for controversy that intensified during the last decade

For decades, scientists have considered that female mammals are born with a lifetime reserve of oocytes in the ovary, irrevocably fated to decline after birth. However, controversy in the matter of the possible presence of oocytes and granulosa cells that originate from stem cells in the adult mammalian ovaries has been expanded. The restricted supply of oocytes in adult female mammals has been disputed in recent years by supporters of neo-oogenesis, who claim that germline stem cells (GSCs) exist in the ovarian surface epithelium (OSE) or the bone marrow (BM). Differentiation of ovarian stem cells (OSCs) into oocytes, fibroblast-like cells, granulosa phenotype, neural and mesenchymal type cells and generation of germ cells from OSCs under the contribution of an OSC niche that consists of immune system-related cells and hormonal signalling has been claimed. Although these arguments have met with intense suspicion, their confirmation would necessitate the revision of the current classic knowledge of female reproductive biology.

Very small embryonic-like stem cells (VSELs) represent a real challenge in stem cell biology: recent pros and cons in the midst of a lively debate

The concept that adult tissue, including bone marrow (BM), contains early-development cells with broader differentiation potential has again been recently challenged. In response, we would like to review the accumulated evidence from several independent laboratories that adult tissues, including BM, harbor a population of very rare stem cells that may cross germ layers in their differentiation potential. Thus, the BM stem cell compartment hierarchy needs to be revisited. These dormant, early-development cells that our group described as very small embryonic-like stem cells (VSELs) most likely overlap with similar populations of stem cells that have been identified in adult tissues by other investigators as the result of various experimental strategies and have been given various names. As reported, murine VSELs have some pluripotent stem cell characteristics. Moreover, they display several epiblast/germline markers that suggest their embryonic origin and developmental deposition in adult BM. Moreover, at the molecular level, changes in expression of parentally imprinted genes (for example, Igf2–H19) and resistance to insulin/insulin-like growth factor signaling (IIS) regulates their quiescent state in adult tissues. In several emergency situations related to organ damage, VSELs can be activated and mobilized into peripheral blood, and in appropriate animal models they contribute to tissue organ/regeneration. Interestingly, their number correlates with lifespan in mice, and they may also be involved in some malignancies. VSELs have been successfully isolated in several laboratories; however, some investigators experience problems with their isolation.