Derivation of embryonic germ cells and male gametes from embryonic stem cells

Downregulation of microRNA-218 is cardioprotective against cardiac fibrosis and cardiac function impairment in myocardial infarction by binding to MITF

OBJECTIVE

This study is intended to figure out the function of microRNA-218 (miR-218) together with microphthalmia-associated transcription factor (MITF) on the cardiac fibrosis and cardiac function impairment in rat models of myocardial infarction (MI).

RESULTS

The rats with MI exhibited cardiac function impairment, cardiac fibrosis, oxidative stress, cardiomyocyte apoptosis, as well as inflammatory injury. Additionally, upregulated miR-218 and downregulated MITF were detected in cardiac tissues of MI rats. MI rats injected with miR-218 inhibitors or overexpressed MITF exhibited elevated MITF expression, improved cardiac function, and diminished pathological damages, infarct size, cardiomyocyte apoptosis, cardiac fibrosis, oxidative stress as well as inflammatory injury in cardiac tissues. Furthermore, downregulated miR-218 and MITF aggravated the conditions than downregulation of miR-218 alone in MI rats.

METHODS

MI models were performed in rats, and then the rats were injected with miR-218 inhibitors and/or MITF overexpression plasmid to elucidate the role of miR-218 and/or MITF on the cardiac function, pathological damage, cardiac fibrosis, angiogenesis, oxidative stress and inflammatory injury of cardiac tissues in MI rats by performing a series of assays.

CONCLUSION

Collectively, we found that the suppression of miR-218 alleviates cardiac fibrosis and cardiac function impairment, and stimulates angiogenesis in MI rats through inhibiting MITF.

Germline DNA replication timing shapes mammalian genome composition

Mammalian DNA replication is a highly organized and regulated process. Large, Mb-sized regions are replicated at defined times along S-phase. Replication Timing (RT) is thought to play a role in shaping the mammalian genome by affecting mutation rates. Previous analyses relied on somatic RT profiles. However, only germline mutations are passed on to offspring and affect genomic composition. Therefore, germ cell RT information is necessary to evaluate the influences of RT on the mammalian genome. We adapted the RT mapping technique for limited amounts of cells, and measured RT from two stages in the mouse germline - primordial germ cells (PGCs) and spermatogonial stem cells (SSCs). RT in germline cells exhibited stronger correlations to both mutation rate and recombination hotspots density than those of RT in somatic tissues, emphasizing the importance of using correct tissues-of-origin for RT profiling. Germline RT maps exhibited stronger correlations to additional genetic features including GC-content, transposable elements (SINEs and LINEs), and gene density. GC content stratification and multiple regression analysis revealed independent contributions of RT to SINE, gene, mutation, and recombination hotspot densities. Together, our results establish a central role for RT in shaping multiple levels of mammalian genome composition.

Modern Technologies Deriving Human Primordial Germ Cells in vitro

Primordial germ cells (PGCs) are a unique type of stem cells capable of giving rise to totipotent stem cells and ensuring the fertility of an organism and the transfer of its genome to the next generation. PGC research is an important perspective research field of developmental biology that handles many questions of embryogenesis and holds promise for treatments of infertility in the future. Considering ethical concerns related to human embryos, the main research approach in understanding the biology of human PGCs is in vitro studies. In this review, we consider the historical perspective of human PGC studies in vitro, the main existing models, and further outlooks and applications in medicine and science.

Comparison of Germ Cell Gene Expressions in Spontaneous Monolayer versus Embryoid Body Differentiation of Mouse Embryonic Stem Cells toward Germ Cells

Background

Genetic and morphologic similarities between mouse embryonic stem cells (ESCs) and primordial germ cells (PGCs) make it difficult to distinguish differentiation of these two cell types in vitro. Using specific GC markers expressed in low level or even not expressed in ESCs- can help recognize differentiated cells in vitro. We attempted to differentiate the mouse ESCs into Gc-like cells spontaneously in monolayer and EB culture method.

Materials and Methods

In this experimental study, we attempted to differentiate ESCs, Oct4-GFP OG2, into GC-like cells (GCLCs) spontaneously in two different ways, including: i. Spontaneous differentiation of ESCs in monolayer culture as (SP) and ii. Spontaneous differentiation of ESCs using embryoid body (EB) culture method as (EB+SP). During culture, expression level of four GC specific genes (Fkbp6, Mov10l1, Riken and Tex13) and Mvh, Scp3, Stra8, Oct4 were evaluated.

Results

In both groups, Mov10l1 was down-regulated (P=0.3), while Tex13 and Riken were up-regulated (P=0.3 and P=0.04, respectively). Fkbp6 and Stra8 were decreased in EB+SP and they were increased in SP group, while no significant difference was determined between them (P=0.1, P=0.07). Additionally, in SP group, gene expression of Mvh and Scp3 were up-regulated and they had significant differences compared to EB+SP group (P=0.00 and P=0.01, respectively). Oct4 was down-regulated in the both groups. Flow-cytometry analysis showed that mean number of Mvh-positive cells in the SP group was significantly greater compared to ESCs, EB+SP and EB7 groups (P=0.00, P=0.01, and P=0.3, respectively).

Conclusion

These findings showed that ESCs were differentiated into GCLCs in both group. But spontaneous dif- ferentiation of ESCs into GCLCs in SP group (monolayer culture) compared to EB+SP (EB culture methods) has more ability to express GCs markers.

An alternative to sexual reproduction: artificial gametes and their implications for society

INTRODUCTION

Artificial gametes (AGs) are cells that have been 'reprogrammed' to function as sperm or eggs. Such cells may in the future enable people who cannot produce gametes, to have genetically-related offspring. In this paper, I consider the prospect of AGs in the context of declining birthrates and postponed parenthood across the Western world.

SOURCES OF DATA

The data quoted in this paper is gathered from a range of sources, encompassing both scientific, demographic and philosophical work.

AREAS OF AGREEMENT

Fertility decline in Western democracies is a widely recognised phenomenon, and postponement of parenthood is regarded as a significant contributing factor in this phenomenon.

AREAS OF CONTROVERSY

It is not clear at what point, if ever, AGs might come into clinical use. There is dispute as to what is the best approach to declining fertility rates in developed countries.

GROWING POINTS

Technologically-assisted reproduction is becoming a more common phenomenon as fertility rates fall and maternal age increases. AGs could offer new ways in which to prolong fertility.

AREAS TIMELY FOR DEVELOPING RESEARCH

More research into the development of AGs is required. There is a need for close analysis of the possible causes of declining fertility and the ways in which societies might respond to these challenges.

Induction of goat bone marrow mesenchymal stem cells into putative male germ cells using mRNA for STRA8, BOULE and DAZL

Bone mesenchymal stem cells (BMSCs) have the capacity to differentiate into germ cells (GCs). This study was conducted to develop a non-integrated method of using RNA transfection to derive putative male GCs from goat BMSCs (gBMSCs) in vitro by overexpressing STRA8, BOULE and DAZL. The gBMSCs were induced by co-transfection these three mRNAs together (mi-SBD group) or sequential transfection according to their expression time order in vivo (mi-S + BD group). After transfection, a small population of gBMSCs transdifferentiated into early germ cell-like cells and had the potential to enter meiosis. These cells expressed primordial germ cell specific genes STELLA, C-KIT and MVH, as well as premeiotic genes DAZL, BOULE, STRA8, PIWIL2 and RNF17. Importantly, the expression level of meiotic marker synaptonemal complex protein 3 significantly increased in these transfected two groups compared with control cells by qRT-PCR, immunofluorescence and western blot analysis (P < 0.05). Moreover, the protein expression of MVH was significantly higher in mi-S + BD group than that in mi-SBD group (P < 0.05). In addition, compared with control group, the methylation rate of imprinted gene H19 decreased in these two transfected group (P < 0.05), and the rate was significantly lower in mi-S + BD group compared with mi-SBD group (P < 0.05). This study helps to understand the mechanisms of action of key genes in GCs differentiation and also provides a novel system for in vitro induction of male GCs from stem cells.

Reconstitution of male germline cell specification from mouse embryonic stem cells using defined factors in vitro

In vitro induction of functional haploid cells from embryonic stem cells (ESCs) has been reported by several groups. However, these reports either involve complex induction process with undefined induction factors or show low-induction efficiency. Here, we report complete meiosis in vitro from ESCs with defined induction factors. ESCs were first induced into primordial germ cell-like cells, which were further induced into male germline cells, including spermatogonial stem cell-like cells (SSCLCs) and spermatid-like cells. Importantly, the obtained SSCLCs were functional as infertile male mice sired healthy offspring via SSCLC transplantation. Further, we found that eukaryotic translation initiation factor 2 subunit 3 and structural gene Y-linked (Eif2s3y) was essential for spermatogenesis. Eif2s3y-overexpressing ESCs showed enhanced spermatogenesis in vitro, as demonstrated by higher expression levels of SSC-specific markers during SSCLC induction process, improved reproductive ability recovery of infertile male mice, and increased efficiency of haploid cell induction. Our work provides a convenient and efficient approach to obtain functional male germline cells.

Stem cells on regenerative and reproductive science in domestic animals

Stem cells are undifferentiated and self-renewable cells that present new possibilities for both regenerative medicine and the understanding of early mammalian development. Adult multipotent stem cells are already widely used worldwide in human and veterinary medicine, and their therapeutic signalling, particularly with respect to immunomodulation, and their trophic properties have been intensively studied. The derivation of embryonic stem cells (ESCs) from domestic species, however, has been challenging, and the poor results do not reflect the successes obtained in mouse and human experiments. More recently, the generation of induced pluripotent stem cells (iPSCs) via the forced expression of specific transcription factors has been demonstrated in domestic species and has introduced new potentials in regenerative medicine and reproductive science based upon the ability of these cells to differentiate into a variety of cells types in vitro. For example, iPSCs have been differentiated into primordial germ-like cells (PGC-like cells, PGCLs) and functional gametes in mice. The possibility of using iPSCs from domestic species for this purpose would contribute significantly to reproductive technologies, offering unprecedented opportunities to restore fertility, to preserve endangered species and to generate transgenic animals for biomedical applications. Therefore, this review aims to provide an updated overview of adult multipotent stem cells and to discuss new possibilities introduced by the generation of iPSCs in domestic animals, highlighting the possibility of generating gametes in vitro via PGCL induction.

Gametogenesis: A journey from inception to conception

Gametogenesis, the process of forming mature germ cells, is an integral part of both an individual's and a species' health and well-being. This chapter focuses on critical male and female genetic and epigenetic processes underlying normal gamete formation through their differentiation to fertilization. Finally, we explore how knowledge gained from this field has contributed to progress in areas with great clinical promise, such as in vitro gametogenesis.

Indirect Co-Culture of Testicular Cells with Bone Marrow Mesenchymal Stem Cells Leads to Male Germ Cell-Specific Gene Expressions

Objective

Non-obstructive azoospermia is mostly irreversible. Efforts to cure this type of infertility have led to the application of stem cells in the reproduction field. In the present study, testicular cell-mediated differentiation of male germ-like cells from bone marrow-derived mesenchymal stem cells (BM-MSCs) in an in vitro indirect co-culture system is investigated.

Materials and Methods

In this experimental study, mouse BM-MSCs were isolated and cultured up to passage three. Identification of the cells was evaluated using specific surface markers by flow-cytometry technique. Four experimental groups were investigated: control, treatment with retinoic acid (RA), indirect co-culture with testicular cells, and combination of RA and indirect co-culture with testicular cells. Finally, following differentiation, the quantitative expression of germ cell-specific markers including Dazl, Piwil2 and Stra8 were evaluated by real-time polymerase chain reaction (PCR).

Results

Molecular analysis revealed a significant increase in Dazl expression in the indirect co-culture with testicular cells group in comparison to the control group. Quantitative expression level of Piwil2 was not significantly changed in comparison to the control group. Stra8 expression was significantly higher in RA group in comparison to other groups.

Conclusion

Indirect co-culture of BM-MSCs in the presence of testicular cells leads to expression of male germ cell-specific gene, Dazl, in the induced cells. Combination of co-culture with testicular cells and RA did not show any positive effect on the specific gene expressions.

The role of microRNAs in embryonic stem cell and induced pluripotent stem cell differentiation in male germ cells

New perspectives have been opened by advances in stem cell research for reproductive and regenerative medicine. Several different cell types can be differentiated from stem cells (SCs) under suitable in vitro and in vivo conditions. The differentiation of SCs into male germ cells has been reported by many groups. Due to their unlimited pluripotency and self-renewal, embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) can be used as valuable tools for drug delivery, disease modeling, developmental studies, and cell-based therapies in regenerative medicine. The unique features of SCs are controlled by a dynamic interplay between extrinsic signaling pathways, and regulations at epigenetic, transcriptional and posttranscriptional levels. In recent years, significant progress has been made toward better understanding of the functions and expression of specific microRNAs (miRNAs) in the maintenance of SC pluripotency. miRNAs are short noncoding molecules, which play a functional role in the regulation of gene expression. In addition, the important regulatory role of miRNAs in differentiation and dedifferentiation has been recently demonstrated. A balance between differentiation and pluripotency is maintained by miRNAs in the embryo and stem cells. This review summarizes the recent findings about the role of miRNAs in the regulation of self-renewal and pluripotency of iPSCs and ESCs, as well as their impact on cellular reprogramming and stem cell differentiation into male germ cells.

Mesenchymal Stem Cells (MSCs) Therapy for Recovery of Fertility: a Systematic Review

In recent years, the mesenchymal stem cells (MSCs) have provided the new opportunities to treat different disorders including infertility. Different studies have suggested that the MSCs have ability to differentiate into germ-like cells under specific induction conditions as well as transplantation to gonadal tissues. The aim of this systematic review was to evaluate the results obtained from different studies on MSCs therapy for promoting fertility. This search was done in PubMed and Science Direct databases using key words MSCs, infertility, therapy, germ cell, azoospermia, ovarian failure and mesenchymal stem cell. Among the more than 11,400 papers, 53 studies were considered eligible for more evaluations. The obtained results indicated that the most studies were performed on MSCs derived from bone marrow and umbilical cord as compared with the other types of MSCs. Different evaluations on animal models as well as in vitro studies supported from their role in the recovery of spermatogenesis and folliculogenesis. Although the data obtained from this systematic review are promising, but the further studies need to assess the efficiency and safety of transplantation of these cells in fertility recovery.

Committing the primordial germ cell: An updated molecular perspective

The germ line is a crucial cell lineage that is distinct from somatic cells, and solely responsible for the trans-generational transmission of hereditary information in metazoan sexual reproduction. Primordial germ cells (PGCs)-the precursors to functional germ cells-are among the first cell types to be allocated in embryonic development, and this lineage commitment is a critical event in partitioning germ line and somatic tissues. Classically, mammalian PGC development has been largely informed by investigations on mouse embryos and embryonic stem cells. Recent findings from corresponding nonrodent systems, however, have indicated that murine PGC specification may not be fully archetypal. In this review, we outline the current understanding of molecular mechanisms in PGC specification, emphasizing key transcriptional events, and focus on salient differences between early human and mouse PGC commitment. Beyond these latest findings, we also contemplate the future outlook of inquiries in this field, highlighting the importance of comprehensively understanding early fate decisions that underlie the segregation of this unique lineage. This article is categorized under: Developmental Biology > Stem Cell Biology and Regeneration Biological Mechanisms > Cell Fates Physiology > Mammalian Physiology in Health and Disease.

Noncanonical translation via deadenylated 3' UTRs maintains primordial germ cells

Primordial germ cells (PGCs) form during early embryogenesis with a supply of maternal mRNAs that contain shorter poly(A)-tails. How translation of maternal mRNAs is regulated during PGC development remains elusive. Here we describe a small molecule screen with zebrafish embryos that identified primordazine, a compound that selectively ablates PGCs. Primordazine’s effect on PGCs arises from translation repression through primordazine-response elements in the 3′UTRs. Systematic dissection of primordazine’s mechanism of action revealed that translation of mRNAs during early embryogenesis occurs by two distinct pathways, depending on the length of their poly(A)-tails. In addition to poly(A)-tail dependent translation (PAT), early embryos perform poly(A)-tail independent non-canonical translation (PAINT) via deadenylated 3′UTRs. Primordazine inhibits PAINT without inhibiting PAT, an effect that was also observed in quiescent but not in proliferating mammalian cells. These studies reveal that PAINT is an alternative form of translation in the early embryo and is indispensable for PGC maintenance.

Recent progress in understanding the mechanisms of Leydig cell differentiation

Leydig cells in fetal and adult testes play pivotal roles in eliciting male characteristics by producing androgen. Although numerous studies of Leydig cells have been performed, the mechanisms for differentiation of the two cell types (fetal Leydig and adult Leydig cells), their developmental and functional relationship, and their differential characteristics remain largely unclear. Based on recent technical progress in genome-wide analysis and in vitro investigation, novel and fascinating observations concerning the issues above have been obtained. Focusing on fetal and adult Leydig cells, this review summarizes the recent progress that has advanced our understanding of the cells.

Application of induced pluripotent stem cell and embryonic stem cell technology to the study of male infertility

Stem cells (SCs) are classes of undifferentiated biological cells existing only at the embryonic, fetal, and adult stages that can divide to produce specialized cell types during fetal development and remain in our bodies throughout life. The progression of regenerative and reproductive medicine owes the advancement of respective in vitro and in vivo biological science on the stem cell nature under appropriate conditions. The SCs are promising therapeutic tools to treat currently of infertility because of wide sources and high potency to differentiate. Nevertheless, no effective remedies are available to deal with severe infertility due to congenital or gonadotoxic stem cell deficiency in prepubertal childhood. Some recent solutions have been developed to address the severe fertility problems, including in vitro formation of germ cells from stem cells, induction of pluripotency from somatic cells, and production of patient-specific pluripotent stem cells. There is a possibility of fertility restoration using the in vitro formation of germ cells from somatic cells. Accordingly, the present review aimed at studying the literature published on the medical application of stem cells in reproductive concerns.

Bovine lineage specification revealed by single-cell gene expression analysis from zygote to blastocyst

Preimplantation embryos undergo zygotic genome activation and lineage specification resulting in three distinct cell types in the late blastocyst. The molecular mechanisms underlying this progress are largely unknown in bovines. Here, we sought to analyze an extensive set of regulators at the single-cell level to define the events involved in the development of the bovine blastocyst. Using a quantitative microfluidics approach in single cells, we analyzed mRNA levels of 96 genes known to function in early embryonic development and maintenance of stem cell pluripotency in parallel in 384 individual cells from bovine preimplantation embryos. The developmental transitions can be distinguished by distinctive gene expression profiles and we identified NOTCH1, expressed in early developmental stages, while T-box 3 (TBX3) and fibroblast growth factor receptor 4 (FGFR4), expressed in late developmental stages. Three lineages can be segregated in bovine expanded blastocysts based on the expression patterns of lineage-specific genes such as disabled homolog 2 (DAB2), caudal type homeobox 2 (CDX2), ATPase H+/K+ transporting non-gastric alpha2 subunit (ATP12A), keratin 8 (KRT8), and transcription factor AP-2 alpha (TFAP2A) for trophectoderm; GATA binding protein 6 (GATA6) and goosecoid homeobox (GSC) for primitive endoderm; and Nanog homeobox (NANOG), teratocarcinoma-derived growth factor 1 (TDGF1), and PR/SET domain 14 (PRDM14) for epiblast. Moreover, some lineage-specific genes were coexpressed in blastomeres from the morula. The commitment to trophectoderm and inner cell mass lineages in bovines occurs later than in the mouse, and KRT8 might be an earlier marker for bovine trophectoderm cells. We determined that TDGF1 and PRDM14 might play pivotal roles in the primitive endoderm and epiblast specification of bovine blastocysts. Our results shed light on early cell fate determination in bovine preimplantation embryos and offer theoretical support for deriving bovine embryonic stem cells.

Differentiation of female Oct4-GFP embryonic stem cells into germ lineage cells

Due to high infertility ratio nowadays, it is essential to explore efficient ways of enhancing mammalian reproductivity, in particular female reproductivity. Using female Oct4-GFP embryonic stem cells, we mimic the in vivo development procedure to induce ES cells into epiblast cell-like cells (EpiLCs) and then primordial germ cell-like cells (PGCLCs). GFP positive PGCLCs that showed typical PGC markers and epigenetic modification were efficiently obtained. Further transplantation of the GFP positive PGCLC and native ovary cell mixture into ovary of infertile mice revealed that both MVH and GFP positive cells could be developed in ovary, but no later developmental stage germ cells were observed. This study suggested that Oct4-GFP ES cells may be only suitable for tracing early germ cell development.

Recent advances of in vitro culture systems for spermatogonial stem cells in mammals

BACKGROUND

Spermatogonial stem cells (SSCs) in the mammalian testis are unipotent stem cells for spermatozoa. They show unique cell characteristics as stem cells and germ cells after being isolated from the testis and cultured in vitro. This review introduces recent progress in the development of culture systems for the establishment of SSC lines in mammalian species, including humans.

METHODS

Based on the published reports, the isolation and purification of SSCs, identification and characteristics of SSCs, and culture system for mice, humans, and domestic animals have been summarized.

RESULTS

In mice, cell lines from SSCs are established and can be reprogrammed to show pluripotent stem cell potency that is similar to embryonic stem cells. However, it is difficult to establish cell lines for animals other than mice because of the dearth of understanding about species-specific requirements for growth factors and mechanisms supporting the self-renewal of cultured SSCs. Among the factors that are associated with the development of culture systems, the enrichment of SSCs that are isolated from the testis and the combination of growth factors are essential.

CONCLUSION

Providing an example of SSC culture in cattle, a rational consideration was made about how it can be possible to establish cell lines from neonatal and immature testes.

Induction of Human Adipose-Derived Mesenchymal Stem Cells into Germ Lineage Using Retinoic Acid

Accumulating evidence indicates that mesenchymal stem cells (MSCs) have been widely used in tissue engineering and regenerative medicine due to their multilineage differentiation potentials. Recent studies show that germ-like cells can also be derived from stem cells, such as human umbilical cord MSCs and human bone marrow MSCs in vitro. However, whether human adipose-derived MSCs (hAD-MSCs) can be induced into germ-like cells has never been reported. In this study, we isolated hAD-MSCs and confirmed that their characteristics were in accordance with that of MSCs established before. Germ cell lineage differentiation was performed by 10 μM retinoic acid (RA) treatment for 21 days. RA induction led to slender spindles and tadpole-like changes of cell morphology, and the expression of germ cell-specific markers (Oct4, Piwil2, Itgb1, SSEA-1, and Stra8) presented significant upregulation in the RA treatment group according to the polymerase chain reaction and immunofluorescence results. We first demonstrated that hAD-MSCs can differentiate into germ-like cells in vitro, which will provide theoretical and experimental basis for the clinical application of hAD-MSCs in the treatment for infertility.

Retinoic acid enhances germ cell differentiation of mouse skin-derived stem cells

BACKGROUND

Retinoic acid (RA) signaling has been identified as a key driver in male and female gamete development. The presence of RA is a critical step in the initiation of meiosis and is required for the production of competent oocytes from primordial germ cells. Meiosis has been identified as a difficult biological process to recapitulate in vitro, when differentiating stem cells to germ cells. We have previously shown that primordial germ cell-like cells, and more advanced oocyte-like cells (OLCs), can be formed by differentiating mouse skin-derived stem cells. However, the OLCs remain unable to function due to what appears to be failure of meiotic initiation. The aim of this study was to determine the effect of RA treatment, during stem cell differentiation to germ cells, particularly on the initiation of meiosis.

RESULTS

Using qPCR we found significant increases in the meiosis markers Stra8 and Sycp3 and a significant reduction in the meiosis inhibitor Nanos2, in the differentiating populations. Furthermore, OLCs from the RA treated group, expressed significantly more of the meiosis regulatory gene Marf1 and the oocyte marker Oct4. At the protein level RA treatment was found to increase the expression of the gap junction protein CX43 and the pluripotency marker OCT4. Moreover, the expression of SYCP3 was significantly upregulated and the localization pattern better matched that of control fetal ovarian cells. RA treatment also improved the structural integrity of the OLCs produced by initiating the expression of all three zona pellucida transcripts (Zp1-3) and improving ZP3 expression levels and localization. Finally, the addition of RA during differentiation led to an almost two-fold increase in the number of OLCs recovered and increased their in vitro growth.

CONCLUSION

RA is a key driver in the formation of functioning gametes and its addition during stem cell to germ cell differentiation improves OLCs entry into meiosis.

Stage-specific approaches promote in vitro induction for spermatogenesis

Spermatogenesis in vitro has been demonstrated using spermatogonial stem cells (SSCs) in monolayer culture or testis tissue fragments in agarose-constructed three-dimensional (3-D) conditions. However, the low efficiency of gamete maturation and the lack of a novel induction platform have limited the progress of its use in further research and clinical applications. Here, we provide modified stage-specific induction approaches for spermatogenesis in in vitro culture with cells possessing a totipotent status. With this stage-specific propagation in a monolayer condition and a changing cytokine combination, we obtained spermatogenic cells in the forward to late meiosis stages with haploid features. Based on this technical platform, we refined a novel serum-free culture system with various cytokines in 3-D Matrigel for spermatogenesis that promote totipotent embryonic stem cells to meiosis stage with distinct SCP3 expression. And we also explored the effects of coculture with fibroblasts, the mutual interactions in the induction conditions promote the mouse embryonic fibroblasts underwent stromal cells differentiation. In further overexpression of spermatogenic gene Dazl in mouse embryonic fibroblasts, we found early stage initiation for spermatogenesis, and that will enhanced if cocultured with embryonic stem cells in the induction condition. Our results provide alternative approaches for effective spermatogenesis and support the development of promising avenues for infertility therapies.

Derivation of male germ cells from induced pluripotent stem cells by inducers: A review

Induced pluripotent stem cells (iPSCs) refer to stem cells that are artificially produced using a new technology known as cellular reprogramming, which can use gene transduction in somatic cells. There are numerous potential applications for iPSCs in the field of stem cell biology becauase they are able to give rise to several different cell features of lineages such as three-germ layers. Primordial germ cells, generated via in vitro differentiation of iPSCs, have been demonstrated to produce functional gametes. Therefore, in this review we discussed past and recent advances in the in vitro differentiation of germ cells using pluripotent stem cells with an emphasis on iPSCs. Although this domain of research is still in its infancy, exploring development mechanisms of germ cells is promising, especially in humans, to promote future reproductive and developmental engineering technologies. While few studies have evaluated the ability and efficiency of iPSCs to differentiate toward male germ cells in vitro by different inducers, the given effect was investigated in this review.

Nascent Induced Pluripotent Stem Cells Efficiently Generate Entirely iPSC-Derived Mice while Expressing Differentiation-Associated Genes

The ability of induced pluripotent stem cells (iPSCs) to differentiate into all adult cell types makes them attractive for research and regenerative medicine; however, it remains unknown when and how this capacity is established. We characterized the acquisition of developmental pluripotency in a suitable reprogramming system to show that iPSCs prior to passaging become capable of generating all tissues upon injection into preimplantation embryos. The developmental potential of nascent iPSCs is comparable to or even surpasses that of established pluripotent cells. Further functional assays and genome-wide molecular analyses suggest that cells acquiring developmental pluripotency exhibit a unique combination of properties that distinguish them from canonical naive and primed pluripotency states. These include reduced clonal self-renewal potential and the elevated expression of differentiation-associated transcriptional regulators. Our observations close a gap in the understanding of induced pluripotency and provide an improved roadmap of cellular reprogramming with ramifications for the use of iPSCs.

The differentiation potential of adipose tissue-derived mesenchymal stem cells into cell lineage related to male germ cells

ABSTRACT The adipose tissue is a reliable source of Mesenchymal stem cells (MSCs) showing a higher plasticity and transdifferentiation potential into multilineage cells. In the present study, adipose tissue-derived mesenchymal stem cells (AT-MSCs) were isolated from mice omentum and epididymis fat depots. The AT-MSCs were initially compared based on stem cell surface markers and on the mesodermal trilineage differentiation potential. Additionally, AT-MSCs, from both sources, were cultured with differentiation media containing retinoic acid (RA) and/or testicular cell-conditioned medium (TCC). The AT-MSCs expressed mesenchymal surface markers and differentiated into adipogenic, chondrogenic and osteogenic lineages. Only omentum-derived AT-MSCs expressed one important gene marker related to male germ cell lineages, after the differentiation treatment with RA. These findings reaffirm the importance of adipose tissue as a source of multipotent stromal-stem cells, as well as, MSCs source regarding differentiation purpose.

Generation of germ cells from pluripotent stem cells in mammals

Background

The germ cell lineage transmits genetic and epigenetic information to the next generation. Primordial germ cells (PGCs), the early embryonic precursors of sperm or eggs, have been studied extensively. Recently, in vitro models of PGC induction have been established in the mouse. Many attempts are reported to enhance our understanding of PGC development in other mammals, including human.

Methods

Here, original and review articles that have been published on PubMed are reviewed in order to give an overview of the literature that is focused on PGC development, including the specification of in vivo and in vitro in mice, human, porcine, and bovine.

Results

Mammalian PGC development, in vivo and in vitro, have been studied primarily by using the mouse model as a template to study PGC specification in other mammals, including human, porcine, and bovine.

Conclusion

The growing body of published works reveals similarities, as well as differences, in PGC establishment in and between mouse and human.

Differentiation of Mouse Ovarian Stem Cells Toward Oocyte-Like Structure by Coculture with Granulosa Cells

An increasing body of evidence has confirmed existence and function of ovarian stem cells (OSCs). In this study, a novel approach on differentiation of OSCs into oocyte-like cells (OLCs) has been addressed. Recently, different methods have been recruited to isolate and describe aspects of OSCs, but newer and more convenient strategies in isolation are still growing. Herein, a morphology-based method was used to isolate OSCs. Cell suspension of mouse neonatal ovaries was cultured and formed colonies were harvested mechanically and cultivated on mouse embryonic fibroblasts. For differentiation induction, colonies transferred on inactive granulosa cells. Results showed that cells in colonies were positive for alkaline phosphatase activity and reverse transcription-polymerase chain reaction (RT-PCR) confirmed the pluripotency characteristics of cells. Immunofluorescence revealed a positive signal for OCT4, DAZL, MVH, and SSEA1 in colonies as well. Results of RT-PCR and immunofluorescence confirmed that some OLCs were generated within the germ stem cell (GSCs) colonies. The applicability of morphological selection for isolation of GSCs was verified. This method is easier and more economic than other techniques. Our results demonstrate that granulosa cells were effective in inducing the differentiation of OSCs into OLCs through direct cell-to-cell contacts.

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

Infertile couples including cancer survivors stand to benefit from gametes differentiated from embryonic or induced pluripotent stem (ES/iPS) cells. It remains challenging to convert human ES/iPS cells into primordial germ-like cells (PGCLCs) en route to obtaining gametes. Considerable success was achieved in 2016 to obtain fertile offspring starting with mouse ES/iPS cells, however the specification of human ES/iPS cells into PGCLCs in vitro is still not achieved. Human ES cells will not yield patient-specific gametes unless and until hES cells are derived by somatic cell nuclear transfer (therapeutic cloning) whereas iPS cells retain the residual epigenetic memory of the somatic cells from which they are derived and also harbor genomic and mitochondrial DNA mutations. Thus, they may not be ideal starting material to produce autologus gametes, especially for aged couples. Pluripotent, very small embryonic-like stem cells (VSELs) have been reported in adult tissues including gonads, are relatively quiescent in nature, survive oncotherapy and can be detected in aged, non-functional gonads. Being developmentally equivalent to PGCs (natural precursors to gametes), VSELs spontaneously differentiate into gametes in vitro. It is also being understood that gonadal stem cells niche is compromised by oncotherapy and with age. Improving the gonadal somatic niche could regenerate non-functional gonads from endogenous VSELs to restore fertility. Niche cells (Sertoli/mesenchymal cells) can be directly transplanted and restore gonadal function by providing paracrine support to endogenous VSELs. This strategy has been successful in several mice studies already and resulted in live birth in a woman with pre-mature ovarian failure.

Stem cells, in vitro gametogenesis and male fertility

Reconstitution in culture of biological processes, such as differentiation and organization, is a key challenge in regenerative medicine, and one in which stem cell technology plays a central role. Pluripotent stem cells and spermatogonial stem cells are useful materials for reconstitution of germ cell development in vitro, as they are capable of differentiating into gametes. Reconstitution of germ cell development, termed in vitro gametogenesis, will provide an experimental platform for a better understanding of germ cell development, as well as an alternative source of gametes for reproduction, with the potential to cure infertility. Since germ cells are the cells for 'the next generation', both the culture system and its products must be carefully evaluated. In this issue, we summarize the progress in in vitro gametogenesis, most of which has been made using mouse models, as well as the future challenges in this field.

Mouse Germ Cell Development in-vivo and in-vitro

In mammalian development, primordial germ cells (PGCs) represent the initial population of cells that are committed to the germ cell lineage. PGCs segregate early in development, triggered by signals from the extra-embryonic ectoderm. They are distinguished from surrounding cells by their unique gene expression patterns. Some of the more common genes used to identify them are Blimp1, Oct3/4, Fragilis, Stella, c-Kit, Mvh, Dazl and Gcna1. These genes are involved in regulating their migration and differentiation, and in maintaining the pluripotency of these cells.

Recent research has demonstrated the possibility of obtaining PGCs, and subsequently, mature germ cells from a starting population of embryonic stem cells (ESCs) in culture. This phenomenon has been investigated using a variety of methods, and ESC lines of both mouse and human origin. Embryonic stem cells can differentiate into germ cells of both the male and female phenotype and in one case has resulted in the birth of live pups from the fertilization of oocytes with ESC derived sperm. This finding leads to the prospect of using ESC derived germ cells as a treatment for sterility. This review outlines the evolvement of germ cells from ESCs in vitro in relation to in vivo events.

Human embryos from induced pluripotent stem cell-derived gametes: ethical and quality considerations

Protocols for successful differentiation of male and female gametes from induced pluripotent stem cells have been published. Although culture of precursor cells in a natural microenvironment remains necessary to achieve terminal differentiation, the creation of human preimplantation embryos from induced pluripotent stem cell-derived gametes is technically feasible. Such embryos could provide a solution to the scarcity of human cleavage-stage embryos donated for research. Here, we discuss current technology, major research-related ethical concerns and propose the norms that would assure the quality and reliability of such embryos.

Functional role of Forskolin and PD166285 in the development of denuded mouse oocytes

OBJECTIVE

cAMP and mature promoting factor (MPF) play critical roles during the maturation of mammalian oocytes. The aim of this study was to produce the offspring from denuded oocytes (DOs) in mice by regulating cAMP and MPF.

METHODS

In this study, we used DOs at the germinal vesicle (GV) stage in mice and regulated levels of cAMP and MPF in DOs by adding Forskolin and PD166285 during in vitro maturation without follicle stimulating hormone and luteinizing hormone, respectively.

RESULTS

Combined use of 50 μM Forskolin for 3 h and 2.5 μM PD166285 for additional 21 h enhanced the developmental competence of DOs, maturation rate of DOs was 76.71%± 4.11%, blastocyst rate was 18.33%±4.44% after parthenogenetic activation (PA). The DOs could successfully be fertilized with sperm in vitro, cleavage rate was 17.02%±5.82% and blastocyst rate was 5.65%±3.10%. Besides, 2-cell in vitro fertilization embryos from DOs produced 4 normal live offspring (4/34).

CONCLUSION

The results confirmed that the combination of Forskolin and PD166285 can induce DOs to complete meiosis process and produce normal offspring.

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.

Gametogenesis from Pluripotent Stem Cells

The germ cell lineage originates early in development and undergoes a series of complex developmental processes that culminate in the generation of fully matured gametes, the spermatozoa and the oocytes. Remarkably, researchers have been recapitulating these developmental pathways using mouse and human pluripotent stem cells (PSCs). With further studies, including those involving non-human primate models, human gametogenesis may be fully reconstituted from PSCs, which would profoundly facilitate our understanding of human germ cell development and infertility. Here we discuss groundbreaking studies that lay the foundation for this achievement, the current state of the field, and challenges for deriving gametes from hPSCs.

Genome editing and genetic engineering in livestock for advancing agricultural and biomedical applications

Genetic modification of livestock has a longstanding and successful history, starting with domestication several thousand years ago. Modern animal breeding strategies predominantly based on marker-assisted and genomic selection, artificial insemination, and embryo transfer have led to significant improvement in the performance of domestic animals, and are the basis for regular supply of high quality animal derived food. However, the current strategy of breeding animals over multiple generations to introduce novel traits is not realistic in responding to the unprecedented challenges such as changing climate, pandemic diseases, and feeding an anticipated 3 billion increase in global population in the next three decades. Consequently, sophisticated genetic modifications that allow for seamless introgression of novel alleles or traits and introduction of precise modifications without affecting the overall genetic merit of the animal are required for addressing these pressing challenges. The requirement for precise modifications is especially important in the context of modeling human diseases for the development of therapeutic interventions. The animal science community envisions the genome editors as essential tools in addressing these critical priorities in agriculture and biomedicine, and for advancing livestock genetic engineering for agriculture, biomedical as well as "dual purpose" applications.

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.

In vitro differentiation of human embryonic stem cells into ovarian follicle-like cells

Understanding the unique mechanisms of human oogenesis necessitates the development of an in vitro system of stem cell differentiation into oocytes. Specialized cell types and organoids have been derived from human pluripotent stem cells in vitro, but generating a human ovarian follicle remains a challenge. Here we report that human embryonic stem cells can be induced to differentiate into ovarian follicle-like cells (FLCs) in vitro. First, we find that two RNA-binding proteins specifically expressed in germ cells, DAZL and BOULE, regulate the exit from pluripotency and entry into meiosis. By expressing DAZL and BOULE with recombinant human GDF9 and BMP15, these meiotic germ cells are further induced to form ovarian FLCs, including oocytes and granulosa cells. This robust in vitro differentiation system will allow the study of the unique molecular mechanisms underlying human pluripotent stem cell differentiation into late primordial germ cells, meiotic germ cells and ovarian follicles.

Retinoic acid induces differentiation of buffalo (Bubalus bubalis) embryonic stem cells into germ cells

Development of precise and reproducible culture system for in vitro differentiation of embryonic stem (ES) cells into germ cells counts as a major leap forward for understanding not only the remarkable process of gametogenesis, otherwise obscured by limited availability of precursor primordial germ cells (PGCs), but in finally treating the catastrophic infertility. Taking into account the significant role of retinoic acid (RA) during in vivo gametogenesis, we designed the present study to investigate the effects of its stimulation on directing the differentiation of ES cells into germ cells. The effects of RA were analyzed across dose-and-time upon various stages of gametogenesis like PGC induction, meiosis initiation and completion, haploid cell formation and development of the final gamete (oocyte and spermatozoa). Out of the series of RA doses (2, 4, 8, 16, 20 and 30μM), 16μM RA for 8day culture interval was found to induce highest expression of PGC- and meiosis-associated genes like DAZL, VASA, SYCP3, MLH1, TNP1/2 and PRM2, while mature germ cell genes like BOULE and TEKT1 (Spermatocyte markers), GDF9 and ZP2 (Oocyte markers) showed higher expression at 2μM RA dose, suggesting functional concentration-gradient of RA activity. Immunocytochemistry revealed expression of germ lineage-specific markers like: c-KIT, DAZL and VASA (PGC-markers); SYCP3, MLH1 and PROTAMINE1 (Meiotic-markers); ACROSIN and HAPRIN (Spermatocyte-markers); and GDF9 and ZP4 (Oocyte-markers) in optimally differentiated embryoid bodies (EBs) and adherent cultures. We observed significantly reduced (p<0.05) concentration of 5-methyl-2-deoxycytidine in RA-differentiated EBs which is suggestive of the occurrence of methylation erasure. FACS analysis of optimally differentiated cultures detected 3.07% haploid cell population, indicating completion of meiosis. Oocyte-like structures (OLS) were obtained in adherent differentiated cultures. They had a big nucleus and a zona pellucida (ZP4) coat. They showed progression through 2-cell, 4-cell, 8-cell, morula and blastocyst-like structures upon extended culture beyond 14days.

Retinoic acid combined with spermatogonial stem cell conditions facilitate the generation of mouse germ-like cells

Spermatogenic lineage has been directly generated in spermatogonial stem cell (SSC) conditions from human pluripotent stem cells (PSCs). However, it remains unknown whether mouse embryonic stem cells (ESCs) can directly differentiate into advanced male germ cell lineage in the same conditions. Here, we showed rather low efficiency of germ-like cell generation from mouse ESCs in SSC conditions. Interestingly, addition of retinoic acid (RA) into SSC conditions enabled efficient differentiation of mouse ESCs into germ-like cells, as shown by the activation of spermatogenesis-associated genes such as Mvh, Dazl, Prdm14, Stella, Scp1, Scp3, Stra8 and Rec8. In contrast, for cells cultured in control medium, the activation of the above genes barely occurred. In addition, RA with SSC conditions yielded colonies of Acrosin-expressing cells and the positive ratio reached a peak at day 6. Our work thus establishes a simple and cost-efficient approach for male germ like cell differentiation from mouse PSCs and may propose a useful strategy for studying spermatogenesis in vitro.

Combined Treatment with Demecolcine and 6-Dimethylaminopurine during Postactivation Improves Developmental Competence of Somatic Cell Nuclear Transfer Embryos in Pigs

This study determined the effects of postactivation treatment with demecolcine and/or 6-dimethylaminopurine (6-DMAP) on in vivo and in vitro developmental competence of somatic cell nuclear transfer (SCNT) embryos in pigs. SCNT embryos were treated for 4 hours with 0.4 µg/mL demecolcine, 2 mM 6-DMAP, or both after electric activation, then transferred to surrogate pigs or cultured for 7 days. The formation rate of SCNT embryos with a single pronucleus was higher in combined treatment with demecolcine and 6-DMAP (95.2%) than treatment with demecolcine alone (87.1%). Blastocyst formation of SCNT embryos was significantly increased in combined treatment with demecolcine and 6-DMAP (48.7%) compared with demecolcine (22.2%) or 6-DMAP alone (37.3%). Fluctuation of maturation promoting factor activity showed different patterns among various postactivation treatments. Pregnancy was established in 1 of 5 surrogates after transfer of SCNT embryos that were treated with demecolcine and 6-DMAP. The pregnant surrogate delivered one healthy live piglet. The results of our study demonstrated that postactivation treatment with demecolcine and 6-DMAP together improved preimplantation development and supported normal in vivo development of SCNT pig embryos, probably influencing MPF activity and nuclear remodeling, including induction of single pronucleus formation after electric activation.

Of Mice and Men: In Vivo and In Vitro Studies of Primordial Germ Cell Specification

Specification of mouse primordial germ cells (PGCs), the precursors of sperm and eggs, involves three major molecular events: repression of the somatic program, reacquisition of pluripotency, and reprogramming to a unique epigenetic ground state. Gene knockout studies in mouse models, along with global transcriptome analyses, have revealed the key signaling pathways and transcription factors essential for PGC specification. Knowledge obtained from these studies has been utilized extensively to develop robust in vitro PGC induction models not only in mice but also in humans. These models have, in turn, formed the basis for a detailed understanding of the signaling pathways and epigenetic dynamics during in vivo PGC specification and development. Recapitulation of human PGC specification in culture is of tremendous significance for understanding the mechanisms of human germ cell development in normal and disease states and has implications for addressing germ-cell-based causes of infertility.