Bone morphogenetic protein 4 is an efficient inducer for mouse embryonic stem cell differentiation into primordial germ cell

Overexpression of bmp4, dazl, nanos3 and sycp2 in Hu Sheep Leydig Cells Using CRISPR/dcas9 System Promoted Male Germ Cell Related Gene Expression

Simple Summary

Male germ cell development plays a crucial role in male reproduction, and gene expression also presents an essential regulatory role in its development. Many studies have been devoted to the induction and differentiation of pluripotent stem cells into germ cells in vitro. However, the culture system for pluripotent stem cells from domestic animals is not stable, especially in sheep. Our study attempted to transdifferentiate sheep somatic cells into germ cells in vitro by the overexpression of key germ cell related genes, with the aim of perfecting the construction of germ cell research models in vitro. Therefore, we explored the expression pattern of four crucial genes, bmp4, dazl, nanos3 and sycp2, in Hu sheep testicular development, and investigated the potential efficiency of overexpression of the four candidate genes using the CRISPR/dcas9 system in Leydig cells. We revealed that the overexpression of bmp4, dazl, nanos3 and sycp2 can promote the expression of male germ cell related genes. To the best of our knowledge, this is the first study to construct an overexpression induction system using CRISPR/dcas9 technology, and to induce sheep somatic cells into germ cells in vitro.

Abstract

Male germ cells directly affect the reproduction of males; however, their accurate isolation and culture in vitro is extremely challenging, hindering the study of germ cell development and function. CRISPR/dcas9, as an efficient gene reprogramming system, has been verified to promote the transdifferentiation of pluripotent stem cells into male germ cells by editing target genes. In our research, we explored the expression pattern of the germ cell related genes bmp4, dazl,nanos3 and sycp2 in Hu sheep testicular development and constructed the overexpression model using the CRISPR/dcas9 system. The results indicated that four genes showed more expression in testis tissue than in other tissues, and that bmp4, dazl and sycp2 present higher expression levels in nine-month-old sheep testes than in three-month-olds, while nanos3 expressed the opposite trend (p < 0.05). In addition, the expression of four potential genes in spermatogenic cells was slightly different, but they were all expressed in sheep Leydig cells. To verify the potential roles of the four genes in the process of inducing differentiation of male germ cells, we performed cell transfection in vitro. We found that the expression of the germ cell related genes Prdm1, Prdm14, Mvh and Sox17 were significantly increased after the overexpression of the four genes in Leydig cells, and the co-transfection effect was the most significant (p < 0.05). Our results illustrate the crucial functions of bmp4, dazl, nanos3 and sycp2 in Hu sheep testis development and verified the effectiveness of the overexpression model that was constructed using the CRISPR/dcas9 system, which provided a basis for further male germ cell differentiation in vitro.

Narrow H3K4me2 is required for chicken PGC formation

The development of primordial germ cells (PGCs) undergoes epigenetic modifications. The study of histone methylation in regulating PGCs is beneficial to understand the development and differentiation mechanism of germ stem cells. Notably, it provides a theoretical basis for directed induction and mass acquisition in vitro. However, little is known about the regulation of PGC formation by histone methylation. Here, we found the high enrichment of H3K4me2 in the blastoderm, genital ridges, and testis. Chromatin immunoprecipitation sequencing was performed and the results revealed that genomic H3K4me2 is dynamic in embryonic stem cells, PGCs, and spermatogonial stem cells. This trend was consistent with the H3K4me2 enrichment in the gene promoter region. Additionally, narrow region triggered PGC-related genes (Bmp4, Wnt5a, and Tcf7l2) and signaling pathways (Wnt and transforming growth factor-β). After knocking down histone methylase Mll2 in vitro and vivo, the level of H3K4me2 decreased, inhibiting Cvh and Blimp1 expression, then repressing the formation of PGCs. Taken together, our study revealed the whole genome map of H3K4me2 in the formation of PGCs, contributing to improve the epigenetic study in PGC formation and providing materials for bird gene editing and rescue of endangered birds.

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.

Distinct roles of retinoic acid and BMP4 pathways in the formation of chicken primordial germ cells and spermatogonial stem cells

This study demonstrated different effects of bone morphogenetic protein 4 (BMP4) and retinoic acid (RA) signaling on the induction of germ cell formation in chickens. In vitro, BMP4 significantly promoted primordial germ cell (PGC) formation, while RA promoted spermatogonial stem cell (SSC) formation. Hematoxylin-Eosin (HE) staining of reproductive ridge and testicular slices showed that BMP4 signaling was activated during PGC formation but was inhibited during PGC differentiation into SSC. In contrast, RA signaling was significantly activated during PGC differentiation to SSC. Mechanistically, elevated expression of phosphorylated mothers against decapentaplegic homolog 5 (p-Smad5) activated BMP4 signaling, while inhibition of p-Smad5 significantly reduced the PGC formation. Additionally, BMP4 regulated the PGC formation through histone acetylation and DNA methylation in deleted in azoospermia-like (DAZL) gene. Luciferase report showed RA binding to RARα regulated stimulated by RA 8 (Stra8) promoter activity during SSC formation, while mutations in RAR binding sites inhibited the Stra8 expression and SSC formation. Further, both HAT and HDAC regulated the RARα isoform, and HAT binding to RARα activated the Stra8 transcription. RNA-seq of embryonic stem cells (ESC), PGC, and SSC showed inverse expression of genes related to the BMP4 and RA pathways during PGC and SSC formation. Additionally, Smad5 and Smurf were critical for the interactions between the two pathways. Specifically, through Smurf promotion of Smad5 ubiquitination, RA could inhibit the BMP4 signal transduction. In conclusion, the BMP4 and RA signaling pathways play opposing roles in germ cell formation, driven by epigenetic processes such as phosphorylation, ubiquitination, and histone acetylation.

Embryonic stem cell derived germ cells induce spermatogenesis after transplantation into the testes of an adult mouse azoospermia model

The present study aimed to: (i) identify the exogenous factors that allow in vitro differentiation of mouse spermatogonial stem cells (SSCs) from embryonic stem cells (ESCs); (ii) evaluate the effects of Sertoli cells in SSC enrichment; and (iii) assess the success of transplantation using in vitro differentiated SSCs in a mouse busulfan-treated azoospermia model. A 1-day-old embryoid body (EB) received 5 ng/ml of bone morphogenetic protein 4 (BMP4) for 4 days, 3 µM retinoic acid (RA) in a SIM mouse embryo-derived thioguanine and ouabain resistant (STO) co-culture system for 7 days, and was subsequently co-cultured for 2 days with Sertoli cells in the presence or absence of a leukaemia inhibitory factor (LIF), basic fibroblast growth factor (bFGF) and RA composition, and in the presence of these factors in simple culture medium. Higher viability, proliferation and germ cell gene expression were seen in the presence of the LIF, bFGF and RA composition, on top of Sertoli cells. Immunocytochemistry results showed higher CDH1 expression in this group. Sertoli co-culture had no effects on SSC proliferation. Eight weeks after transplantation, injected cells were observed at the base of the seminiferous tubules and in the recipient testes. The number of spermatogonia and the mass of the testes were higher in transplanted testes relative to the control group. It seems that transplantation of these cells can be useful in infertility treatment.

Dynamic expression and regulatory mechanism of TGF-β signaling in chicken embryonic stem cells differentiating into spermatogonial stem cells

The present study investigated the dynamic expression and regulatory mechanism of transforming growth factor β (TGF-β) signaling involved in embryonic stem cells (ESCs) differentiation into male germ cells. Candidate genes involved in TGF-β signaling pathway were screened from RNA-sequencing (RNA-seq), which were further validated by quantitative real-time PCR (qRT-PCR). Bone morphogenetic protein 4 (BMP4) was used to induce differentiation of ESCs in vitro. Inhibition of TGF-β signaling pathway was reflected by Western blot of SMAD2 and SMAD5 expression. Differentiating efficiency of germ cells was evaluated by immunofluorescence and fluorescence-activated cell sorting (FACS). Germ cell marker genes were assessed by qRT-PCR in the differentiation process, with activation or inhibition of TGF-β signaling pathway. In the process of in vitro induction, SMAD2 and SMAD5 were found to significantly up-regulated in BMP4 group versus the control and inhibition groups after 4 and 14 days. Expression of CKIT, CVH, DAZL, STRA8, and INTEGRIN α6 were significantly increased in the BMP4 group compared with the control group, while down-regulated in the inhibition groups. The proportion of germ cell-like cells was decreased from 17.9% to 2.2% after 4 days induction, and further decreased from 14.1% to 2.1% after 14 days induction. Correspondingly, expression of marker genes in germ cells was significantly lower. In vivo inhibition of TGF-β signaling pathway reduced germ cells formation from 5.5% to 1.6%, and down-regulated the expression of CKIT, CVH, DAZL, STRA8, and INTEGRIN α6. In conclusion, our study reveals the mechanism regulating spermatogonial stem cells (SSCs) and lays the basis for further understanding of the regulatory network.

Collagen-alginate microspheres as a 3D culture system for mouse embryonic stem cells differentiation to primordial germ cells

Germ cells differentiation of stem cells will aid treatment of adults with infertility. Biopolymers utilization provided synthetic extracellular matrix (ECM) and desired attributes in in vitro to improve conditions for stem cells attachment, proliferation and differentiation. Mixture of alginate as a biocompatible hydrogel, with collagen IV, could establish an in vitro 3 dimensional (3D) culture model. The objective of this study was investigation of the mouse ESCs differentiation capacity to putative primordial germ cells (PGCs) in the alginate and alginate-collagen IV microspheres (CAM). ESCs aggregated together to form embryoid bodies (EB) in CAM under basal medium supplemented with bone morphogenetic protein-4 (BMP4) as a differentiation factor. Viability and PGC differentiation of the stem cells in microspheres was evaluated by apoptosis and PGC related gene markers. Flow cytometry analysis was also used to detect of Mvh endogenous protein as a specific PGC marker. PGC gene and protein expression revealed that differentiation potential of ESCs to putative PGCs in CAM is significantly higher than control groups. Taking together, it was concluded that CAM demonstrated a great potential to use in PGCs differentiation and treatment of adults with infertility and may be a reliable means of producing mature germ cells.

Proliferation in culture of primordial germ cells derived from embryonic stem cell: induction by retinoic acid

An in vitro system that supports primordial germ cells (PGCs) survival and proliferation is useful for enhancement of these cells and efficient transplantation in infertility disorders. One approach is cultivation of PGCs under proper conditions that allow self-renewal and proliferation of PGCs. For this purpose, we compared the effects of different concentrations of retinoic acid (RA), and the effect of PGCs co-culture (Co-C) with SIM mouse embryo-derived thioguanine- and ouabain-resistant (STO) cells on the proliferation of embryonic stem cells (ESCs)-derived PGCs. One-day-old embryoid body (EB) was cultured for 4 days in simple culture system in the presence of 5 ng/ml bone morphogenetic protein-4 (BMP4) (SCB group) for PGC induction. For PGC enrichment, ESCs-derived germ cells were cultured for 7 days in the presence of different doses (0-5  μM) of RA, both in the simple and STO Co-C systems. At the end of the culture period, viability and proliferation rates were assessed and expression of mouse vasa homologue (Mvh),  α6 integrin,  β1 integrin, stimulated by retinoic acid 8 (Stra8) and piwi (Drosophila)-like 2 (Piwil2) was evaluated using quantitative PCR. Also, the inductive effects were investigated immunocytochemically with Mvh and cadherin1 (CDH1) on the selected groups. Immunocytochemistry/PCR results showed higher expression of Mvh, the PGC-specific marker, in 3  μM RA concentrations on the top of the STO feeder layer. Meanwhile, assessment of the Stra8 mRNA and CDH1 protein, the specific makers for spermatogonia, showed no significant differences between groups. Based on the results, it seems that in the presence of 3 μM RA on top of the STO feeder layer cells, the majority of the cells transdifferentiated into germ cells were PGCs.

In vitro germ cell differentiation from embryonic stem cells of mice: induction control by BMP4 signalling

The present study aims to confirm and analyse germ cell-related patterns and specific gene expressions at a very early stage of cell commitment. Following the XY cytogenetic confirmation of the CCE mouse embryonic stem cells (mESCs) line, cells were cultured to form embryoid bodies (EBs). Expression pattern assessment of the mouse vasa homologue (Mvh), Stra8, α6 and β1 integrin genes in ESC and 1–3-day-old EB showed that all genes except α6 integrin were expressed in the ESC. The mean calibration of Mvh, Stra8 and α6 integrin expression significantly increased upon EB formation compared with the ESCs. During mouse embryogenesis, the signalling of bone morphogenetic protein (BMP) is essential for germ-line formation. To investigate its role in germ-line induction in vitro, mESCs were cultured as 1-day-old EB aggregates with BMP4 for 4 days in STO co-culture systems, in the presence and absence of 5 ng/ml BMP4. At the end of the culture period, colony assay (number and diameter) was performed and the viability percentage and proliferation rate was determined. There were no significant statistical differences in the abovementioned criteria between these two groups. Moreover, the expression of Mvh, α6 and β1 integrins, Stra8 and Piwil2 genes was evaluated in co-culture groups. The molecular results of co-culture groups showed higher–but insignificant–Piwil2 and significant α6 integrin expressions in BMP4 treated co-culture systems. These results confirmed that the EB system and the presence of BMP4 in a STO co-culture system improve the differentiation of ESCs to germ cell.

In vitro effects of date palm (Phoenix dactylifera L.) pollen on colonization of neonate mouse spermatogonial stem cells

ETHNOPHARMACOLOGICAL RELEVANCE

Date palm (Phoenix dactylifera L.) pollen (DPP) is widely used as a folk remedy for male infertility treatment, and has well known medicinal effects.

AIM OF THE STUDY

This study aimed to determine the in vitro effects of DPP on the efficiency of neonate mouse spermatogonial stem cells (SSCs) proliferation.

MATERIAL AND METHODS

Sertoli and SSCs were isolated from 6 to 10-days-old mouse testes, and their identity was confirmed using immunocytochemistry against cytokeratin for sertoli cells and PLZF, Oct-4 and CDH-1 for SSCs. Isolated testicular cells were cultured in the absence or presence of 0.06, 0.25 and 0.62mg/ml concentrations of DPP aqueous extract for 2 weeks. The number and diameter of SSC colonies were assessed during third, 7th, 9th and 14th day of culture, and the expression of the Mvh, GFRα-1 and Oct-4 was evaluated using quantitative PCR at the end of the culture period. The significance of the data was analyzed using ANOVA and paired samples t-test and Tukey and Bonferroni test as post hoc tests at the level of p≤0.05.

RESULTS

Pattern assay of colony formation showed that SSCs numbers increased in the present of 0.62mg/ml concentration of DPP extract with higher slop relative to other groups (P <0.05). Colony diameters had no significant difference between groups in 3th, 7th, 9th and 14th days after culture. The Mvh and Oct-4 genes expression had no significant difference between groups, while GFRα1 expression was increased significantly in cells treated with 0.06mg/ml concentration relative to other groups (P<0.05).

CONCLUSION

It seems that co-culture of SSCs with sertoli sells in the presence of low doses of DPP can increase SSCs proliferation and keep their stemness state, while higher concentrations can differentiate the treated cells.

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.

BMP4 promotes SSEA-1(+) hUC-MSC differentiation into male germ-like cells in vitro

OBJECTIVES

Recent studies have demonstrated that primordial germ cells (PGC) can be differentiated from human umbilical cord mesenchymal stem cells (hUC-MSCs), and embryonic stem cells (ESCs) in vitro. Nevertheless, efficiencies were low and unstable. Here, whether hUC-MSCs can be induced to differentiate into germ-like cells with the aid of bone morphogenetic protein (BMP4) was investigated.

MATERIALS AND METHODS

Human umbilical cord mesenchymal stem cells were freshly isolated and cultured with BMP4. SSEA-1(+/-) cells were purified using magnetic-activated cell sorting (MACS) from the hUC-MSCs, and further induced with BMP4. Quantitative real-time PCR (qRT-PCR) and immunofluorescence analysis were used to determine PGC and germ-like cell-specific markers.

RESULTS

Human umbilical cord mesenchymal stem cells differentiated into SSEA-1(+) spherical PGC-like cells efficiently with 12.5 ng/ml BMP4. qRT-PCR and immunofluorescence analysis demonstrated that SSEA-1(+) cells expressed higher levels of PGC-specific markers than SSEA-1(-) cells. Furthermore, SSEA-1(+) cells were induced with BMP4 to differentiate into STRA8, SCP3, DMRT1 and PLZF-positive male germ-like cells, and some sperm-like cells were obtained by 7-14 days after induction.

CONCLUSION

These results suggest that SSEA-1(+) hUC-MSCs can differentiate into male germ-like cells in the presence of BMP4. This study provides an efficient protocol to study germ-cell development using hUC-MSCs.

Small SSEA-4-positive cells from human ovarian cell cultures: related to embryonic stem cells and germinal lineage?

Background

It has already been found that very small embyronic-like stem cells (VSELs) are present in adult human tissues and organs. The aim of this study was to find if there exists any similar population of cells in cell cultures of reproductive tissues and embryonic stem cells, and if these cells have any relation to pluripotency and germinal lineage.

Methods and results

Here we report that a population of small SSEA-4-positive cells with diameters of up to 4 μm was isolated by fluorescence-activated cell sorting (FACS) from the human ovarian cell cultures after enzymatic degradation of adult cortex tissues. These small cells – putative ovarian stem cells – were also observed during cell culturing of up to 6 months and more. In general, small putative ovarian stem cells, isolated by FACS, showed a relatively low gene expression profile when compared to human embryonic stem cells (hESCs) and human adult fibroblasts; this may reflect the quiescent state of these cells. In spite of that, small putative ovarian stem cells expressed several genes related to primordial germ cells (PGCs), pluripotency and germinal lineage, including VASA. The PGC-related gene PRDM1 was strongly expressed in small putative ovarian stem cells; in both hESCs and fibroblasts it was significantly down-regulated. In addition, putative ovarian stem cells expressed other PGC-related genes, such as PRDM14 and DPPA3. Most of the pluripotency and germinal lineage-related genes were up-regulated in hESCs (except VASA). When compared to fibroblasts, there were several pluripotency-related genes, which were up-regulated in small putative ovarian stem cells. Similar populations of small cells were also isolated by FACS from human testicular and hESC cultures.

Conclusions

Our results confirm the potential embryonic-like character of small putative stem cells isolated from human adult ovaries and their possible relation to germinal lineage.

Role of Mael in early oogenesis and during germ-cell differentiation from embryonic stem cells in mice in vitro

In a previous study, we have identified a set of conserved spermatogenic genes whose expression is restricted to testis and ovary and that are developmentally regulated. One of these genes, the transcription factor Mael, has been reported to play an essential role in mouse spermatogenesis. Nevertheless, the role of Mael in mouse oogenesis has not been defined. In order to analyse the role of Mael in mouse oogenesis, the expression of this gene was blocked during early oogenesis in mouse in vitro using RNAi technology. In addition, the role of Mael during differentiation of embryonic stem cells (ESC) into germ cells in vitro was analysed. Results show that downregulation of Mael by a specific short interfering RNA disrupted fetal oocyte growth and differentiation in fetal ovary explants in culture and the expression of several germ-cell markers in ESC during their differentiation. These results suggest that there is an important role for Mael in early oogenesis and during germ-cell differentiation from embryonic stem cells in mouse in vitro.