Induction of Germ Cell-like Cells from Porcine Induced Pluripotent Stem Cells

The Evolutionary Route of in vitro Human Spermatogenesis: What is the Next Destination?

Malfunction in spermatogenesis due to genetic diseases, trauma, congenital disorders or gonadotoxic treatments results in infertility in approximately 7% of males. The behavior of spermatogonial stem cells (SSCs) within three-dimensional, multifactorial, and dynamic microenvironment implicates a niche that serves as a repository for fertility, since can serve as a source of mature and functional male germ cells. Current protocols enable reprogramming of mature somatic cells into induced pluripotent stem cells (iPSCs) and their limited differentiation to SSCs within the range of 0-5%. However, the resulting human iPSC-derived haploid spermatogenic germ cell yield in terms of number and functionality is currently insufficient for transfer to infertility clinic as a therapeutic tool. In this article, we reviewed the evolution of experimental culture platforms and introduced a novel iPSCs-based approach for in vitro spermatogenesis based on a niche perspective bearing cellular, chemical, and physical factors that provide the complex arrangement of testicular seminiferous tubules embedded within a vascularized stroma. We believe that bioengineered organoids supported by smart bio-printed tubules and microfluidic organ-on-a-chip systems offer efficient, precise, personalized platforms for autologous pluripotent stem cell sources to undergo the spermatogenetic cycle, presenting a promising tool for infertile male patients with complete testicular aplasia.

The progress of induced pluripotent stem cells derived from pigs: a mini review of recent advances

Pigs (Sus scrofa) are widely acknowledged as an important large mammalian animal model due to their similarity to human physiology, genetics, and immunology. Leveraging the full potential of this model presents significant opportunities for major advancements in the fields of comparative biology, disease modeling, and regenerative medicine. Thus, the derivation of pluripotent stem cells from this species can offer new tools for disease modeling and serve as a stepping stone to test future autologous or allogeneic cell-based therapies. Over the past few decades, great progress has been made in establishing porcine pluripotent stem cells (pPSCs), including embryonic stem cells (pESCs) derived from pre- and peri-implantation embryos, and porcine induced pluripotent stem cells (piPSCs) using a variety of cellular reprogramming strategies. However, the stabilization of pPSCs was not as straightforward as directly applying the culture conditions developed and optimized for murine or primate PSCs. Therefore, it has historically been challenging to establish stable pPSC lines that could pass stringent pluripotency tests. Here, we review recent advances in the establishment of stable porcine PSCs. We focus on the evolving derivation methods that eventually led to the establishment of pESCs and transgene-free piPSCs, as well as current challenges and opportunities in this rapidly advancing field.

Mechanisms of Embryonic Stem Cell Pluripotency Maintenance and Their Application in Livestock and Poultry Breeding

Embryonic stem cells (ESCs) are remarkably undifferentiated cells that originate from the inner cell mass of the blastocyst. They possess the ability to self-renew and differentiate into multiple cell types, making them invaluable in diverse applications such as disease modeling and the creation of transgenic animals. In recent years, as agricultural practices have evolved from traditional to biological breeding, it has become clear that pluripotent stem cells (PSCs), either ESCs or induced pluripotent stem cells (iPSCs), are optimal for continually screening suitable cellular materials. However, the technologies for long-term in vitro culture or establishment of cell lines for PSCs in livestock are still immature, and research progress is uneven, which poses challenges for the application of PSCs in various fields. The establishment of a robust in vitro system for these cells is critically dependent on understanding their pluripotency maintenance mechanisms. It is believed that the combined effects of pluripotent transcription factors, pivotal signaling pathways, and epigenetic regulation contribute to maintaining their pluripotent state, forming a comprehensive regulatory network. This article will delve into the primary mechanisms underlying the maintenance of pluripotency in PSCs and elaborate on the applications of PSCs in the field of livestock.

Emerging Contributions of Pluripotent Stem Cells to Reproductive Technologies in Veterinary Medicine

The generation of mature gametes and competent embryos in vitro from pluripotent stem cells has been successfully achieved in a few species, mainly in mice, with recent advances in humans and scarce preliminary reports in other domestic species. These biotechnologies are very attractive as they facilitate the understanding of developmental mechanisms and stages that are generally inaccessible during early embryogenesis, thus enabling advanced reproductive technologies and contributing to the generation of animals of high genetic merit in a short period. Studies on the production of in vitro embryos in pigs and cattle are currently used as study models for humans since they present more similar characteristics when compared to rodents in both the initial embryo development and adult life. This review discusses the most relevant biotechnologies used in veterinary medicine, focusing on the generation of germ-cell-like cells in vitro through the acquisition of totipotent status and the production of embryos in vitro from pluripotent stem cells, thus highlighting the main uses of pluripotent stem cells in livestock species and reproductive medicine.

In Vitro Growth of Mammalian Follicles and Oocytes

Mammalian ovaries contain a large number of immature follicles, most of which are destined to degenerate before ovulation [...].

Making human eggs in a dish: are we close?

In the space of 50 years, we have seen incredible achievements in human reproductive medicine. With these leaps forward, it is no wonder that there is a major interest in women's reproductive health research, including extension of reproductive lifespan. Substantial effort is currently being made to address this challenge, including from the commercial sector. In vitro gametogenesis (IVG) in mice is a spectacular breakthrough and has the potential to offer hope to women with intractable infertility. However, with such lofty goals, some reflection may be called for: mastering all of the techniques required for complete and safe IVG in women is likely to be extraordinarily difficult.

Porcine Germ Cells Phenotype during Embryonic and Adult Development

Primordial germ cells (PGCs) are the precursors of gametes. Due to their importance for the formation and reproduction of an organism, understanding the mechanisms and pathways of PGCs and the differences between males and females is essential. However, there is little research in domestic animals, e.g., swine, regarding the epigenetic and pluripotency profiles of PGCs during development. This study analyzed the expression of epigenetic and various pluripotent and germline markers associated with the development and differentiation of PGCs in porcine (pPGCs), aiming to understand the different gene expression profiles between the genders. The analysis of gonads at different gestational periods (from 24 to 35 days post fertilization (dpf) and in adults) was evaluated by immunofluorescence and RT-qPCR and showed phenotypic differences between the gonads of male and female embryos. In addition, the pPGCs were positive for OCT4 and VASA; some cells were H3k27me3 positive in male embryos and adult testes. In adults, the cells of the testes were positive for germline markers, as confirmed by gene expression analysis. The results may contribute to understanding the pPGC pathways during reproductive development, while also contributing to the knowledge needed to generate mature gametes in vitro.

Review: A barnyard in the lab: prospect of generating animal germ cells for breeding and conservation

In vitro gametogenesis (IVG) offers broad opportunities for gaining detailed new mechanistic knowledge of germ cell biology that will enable progress in the understanding of human infertility, as well as for applications in the conservation of endangered species and for accelerating genetic selection of livestock. The realisation of this potential depends on overcoming key technical challenges and of gaining more detailed knowledge of the ontogeny and developmental programme in different species. Important differences in the molecular mechanisms of germ cell determination and epigenetic reprogramming between mice and other animals have been elucidated in recent years. These must be carefully considered when developing IVG protocols, as cellular kinetics in mice may not accurately reflect mechanisms in other mammals. Similarly, diverse stem cell models with potential for germ cell differentiation may reflect alternative routes to successful IVG. In conclusion, the fidelity of the developmental programme recapitulated during IVG must be assessed against reference information from each species to ensure the production of healthy animals using these methods, as well as for developing genuine models of gametogenesis.

Germline stem cells in human

The germline cells are essential for the propagation of human beings, thus essential for the survival of mankind. The germline stem cells, as a unique cell type, generate various states of germ stem cells and then differentiate into specialized cells, spermatozoa and ova, for producing offspring, while self-renew to generate more stem cells. Abnormal development of germline stem cells often causes severe diseases in humans, including infertility and cancer. Primordial germ cells (PGCs) first emerge during early embryonic development, migrate into the gentile ridge, and then join in the formation of gonads. In males, they differentiate into spermatogonial stem cells, which give rise to spermatozoa via meiosis from the onset of puberty, while in females, the female germline stem cells (FGSCs) retain stemness in the ovary and initiate meiosis to generate oocytes. Primordial germ cell-like cells (PGCLCs) can be induced in vitro from embryonic stem cells or induced pluripotent stem cells. In this review, we focus on current advances in these embryonic and adult germline stem cells, and the induced PGCLCs in humans, provide an overview of molecular mechanisms underlying the development and differentiation of the germline stem cells and outline their physiological functions, pathological implications, and clinical applications.

Research progress and application prospects of stable porcine pluripotent stem cells

Pluripotent stem cells (PSCs) harbor the capacity of unlimited self-renewal and multi-lineage differentiation potential which are crucial for basic research and biomedical science. Establishment of PSCs with defined features were previously reported from mice and humans, while generation of stable large animal PSCs has experienced a relatively long trial stage and only recently has made breakthroughs. Pigs are regarded as ideal animal models for their similarities in physiology and anatomy to humans. Generation of porcine PSCs would provide cell resources for basic research, genetic engineering, animal breeding and cultured meat. In this review, we summarize the progress on the derivation of porcine PSCs and reprogrammed cells and elucidate the mechanisms of pluripotency changes during pig embryo development. This will be beneficial for understanding the divergence and conservation between different species involved in embryo development and the pluripotent regulated signaling pathways. Finally, we also discuss the promising future applications of stable porcine PSCs.

Generation of male germ cells in vitro from the stem cells

Infertility has become a serious disease since it affects 10%-15% of couples worldwide, and male infertility contributes to about 50% of the cases. Notably, a significant decrease occurs in the newborn population by 7.82 million in 2020 compared to 2016 in China. As such, it is essential to explore the effective methods of obtaining functional male gametes for restoring male fertility. Stem cells, including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), spermatogonial stem cells (SSCs), and mesenchymal stem cells (MSCs), possess the abilities of both self-renewal and differentiation into germ cells. Significantly, much progress has recently been achieved in the generation of male germ cells in vitro from various kinds of stem cells under the specified conditions, e.g., the coculturing with Sertoli cells, three-dimensional culture system, the addition of growth factors and cytokines, and/or the overexpression of germ cell-related genes. In this review, we address the current advance in the derivation of male germ cells in vitro from stem cells based on the studies of the peers and us, and we highlight the perspectives and potential application of stem cell-derived male gametes in reproductive medicine.

In vitro induced pluripotency from urine-derived cells in porcine

BACKGROUND

The generation of induced pluripotent stem cells (iPSC) has been a game-changer in translational and regenerative medicine; however, their large-scale applicability is still hampered by the scarcity of accessible, safe, and reproducible protocols. The porcine model is a large biomedical model that enables translational applications, including gene editing, long term in vivo and offspring analysis; therefore, suitable for both medicine and animal production.

AIM

To reprogramme in vitro into pluripotency, and herein urine-derived cells (UDCs) were isolated from porcine urine.

METHODS

The UDCs were reprogrammed in vitro using human or murine octamer-binding transcription factor 4 (OCT4), SRY-box2 (SOX2), Kruppel-like factor 4 (KLF4), and C-MYC, and cultured with basic fibroblast growth factor (bFGF) supplementation. To characterize the putative porcine iPSCs three clonal lineages were submitted to immunocytochemistry for alkaline phosphatase (AP), OCT4, SOX2, NANOG, TRA1 81 and SSEA 1 detection. Endogenous transcripts related to the pluripotency (OCT4, SOX2 and NANOG) were analyzed via reverse transcription quantitative real-time polymerase chain reaction in different time points during the culture, and all three lineages formed embryoid bodies (EBs) when cultured in suspension without bFGF supplementation.

RESULTS

The UDCs were isolated from swine urine samples and when at passage 2 submitted to in vitro reprogramming. Colonies of putative iPSCs were obtained only from UDCs transduced with the murine factors (mOSKM), but not from human factors (hOSKM). Three clonal lineages were isolated and further cultured for at least 28 passages, all the lineages were positive for AP detection, the OCT4, SOX2, NANOG markers, albeit the immunocytochemical analysis also revealed heterogeneous phenotypic profiles among lineages and passages for NANOG and SSEA1, similar results were observed in the abundance of the endogenous transcripts related to pluripotent state. All the clonal lineages when cultured in suspension without bFGF were able to form EBs expressing ectoderm and mesoderm layers transcripts.

CONCLUSION

For the first time UDCs were isolated in the swine model and reprogrammed into a pluripotent-like state, enabling new numerous applications in both human or veterinary regenerative medicine.

Vitamin C enhances porcine cloned embryo development and improves the derivation of embryonic stem-like cells

Porcine cloning through somatic cell nuclear transfer (SCNT) has been widely used in biotechnology for generating animal disease models and genetically modified animals for xenotransplantation. Vitamin C is a multifunctional factor that reacts with several enzymes. In this study, we used porcine oocytes to investigate the effects of different concentrations of vitamin C on in vitro maturation (IVM), in vitro culture (IVC), and the derivation of nuclear transfer embryonic stem-like cells (NT-ESCs). We demonstrated that vitamin C promoted the cleavage and blastocyst rate of genetically modified cloned porcine embryos and improved the derivation of NT-ESCs. Vitamin C integrated into IVM and IVC enhanced cleavage and blastocyst formation (P < 0.05) in SCNT embryos. Glutathione level was increased, and reactive oxygen species levels were decreased (P < 0.05) due to vitamin C treatment. Vitamin C decreased the gene expression of apoptosis (BAX) and increased the expression of genes associated with nuclear reprogramming (NANOG, POU5F1, SOX2, c-Myc, Klf4, and TEAD4), antioxidation (SOD1), anti-apoptotic (Bcl2), and trophectoderm (CDX2). Moreover, vitamin C improved the attachment, derivation, and passaging of NT-ESCs, while the control group showed no outgrowths beyond the primary culture. In conclusion, supplementation of vitamin C at a dose of 50 µg/ml to the IVM and IVC culture media was appropriate to improve the outcomes of porcine IVM and IVC and for the derivation of NT-ESCs as a model to study the pre- and post-implantation embryonic development in cloned transgenic embryos. Therefore, we recommend the inclusion of vitamin C as a supplementary factor to IVM and IVC to improve porcine in vitro embryonic development.

Recellularized rat testis scaffolds with embryoid bodies cells: a promising approach for tissue engineering

Tissue engineering is gaining use to investigate the application of its techniques for infertility treatment. The use of pluripotent embryonic cells for in vitro production of viable spermatozoa in testicular scaffolds is a promising strategy that could solve male infertility. Due to cell-extracellular matrix (ECM) interactions, here we aim to investigate the differentiation of embryoid bodies (EBs) in cultured into decellularized rat testis scaffolds. Decellularized testis (P = 0.019) with a low concentration of gDNA (30.58 mg/ng tissue) was obtained by sodium dodecyl sulfate perfusion. The structural proteins (collagens type I and III) and the adhesive glycoproteins of ECM (laminin and fibronectin) were preserved according to histological and scanning electron microscopy (SEM) analyses. Then, decellularized rat testis were cultured for 7 days with EB, and EB mixed with retinoic acid (RA) in non-adherent plates. By SEM, we observe that embryonic stem cells adhered in the decellularized testis ECM. By immunofluorescence, we verified the positive expression of HSD17B3, GDNF, ACRV-1, and TRIM-36, indicating their differentiation using RA in vitro, reinforcing the possibility of EB in male germ cell differentiation. Finally, recellularized testis ECM may be a promising tool for future new approaches for testicular cell differentiation applied to assisted reproduction techniques and infertility treatment.Abbreviations: ACRV-1: Acrosomal vesicle protein 1; ATB: Penicillin-streptomycin; DAPI: 4,6-Diamidino-2-phenylindole; EB: Embryoid bodies; ECM: Extracellular matrix; ESCs: Pluripotent embryonic stem cells; GAGs: Glycosaminoglycans; gDNA: Genomic DNA; GDNF: Glial cell line-derived neurotrophic factor; H&E: Hematoxylin and eosin; HSD17B3: 17-beta-Hydroxysteroid dehydrogenase type 3; PBS: Phosphate-buffered saline; PGCLCs: Primordial germ-cell-like cells; RA: Retinoic acid; SDS: Sodium dodecyl sulfate; SEM: Scanning electron microscopy; SSCs: Spermatogonial stem cells; TRIM-36: Tripartite Motif Containing 36.

Fish Pluripotent Stem-Like Cell Line Induced by Small-Molecule Compounds From Caudal Fin and its Developmental Potentiality

The technique of induced pluripotent stem cells has significant application value in breeding and preserving the genetic integrity of fish species. However, it is still unclear whether the chemically induced pluripotent stem cells can be induced from non-mammalian cells or not. In this article, we first verify that fibroblasts of fish can be chemically reprogrammed into pluripotent stem cells. These induced pluripotent stem-like cells possess features of colony morphology, expression of pluripotent marker genes, formation of embryoid bodies, teratoma formation, and the potential to differentiate into germ cell-like cells in vitro. Our findings will offer a new way to generate induced pluripotent stem cells in teleost fish and a unique opportunity to breed commercial fish and even save endangered fish species.

Porcine Primordial Germ Cell-Like Cells Generated from Induced Pluripotent Stem Cells Under Different Culture Conditions

Culture conditions regulate the process of pluripotency acquisition and self-renewal. This study aimed to analyse the influence of the in vitro environment on the induction of porcine induced pluripotent stem cell (piPSCs) differentiation into primordial germ cell-like cells (pPGCLCs). piPSC culture with different supplementation strategies (LIF, bFGF, or LIF plus bFGF) promoted heterogeneous phenotypic profiles. Continuous bFGF supplementation during piPSCs culture was beneficial to support a pluripotent state and the differentiation of piPSCs into pPGCLCs. The pPGCLCs were positive for the gene and protein expression of pluripotent and germinative markers. This study can provide a suitable in vitro model for use in translational studies and to help answer numerous remaining questions about germ cells.

Production of viable chicken by allogeneic transplantation of primordial germ cells induced from somatic cells

The allogeneic transplantation of primordial germ cells (PGCs) derived from somatic cells overcomes the limitation of avian cloning. Here, we transdifferentiate chicken embryo fibroblasts (CEFs) from black feathered Langshan chickens to PGCs and transplant them into White Plymouth Rock chicken embryos to produce viable offspring with characteristics inherited from the donor. We express Oct4/Sox2/Nanog/Lin28A (OSNL) to reprogram CEFs to induced pluripotent stem cells (iPSCs), which are further induced to differentiate into PGCs by BMP4/BMP8b/EGF. DNA demethylation, histone acetylation and glycolytic activation elevate the iPSC induction efficiency, while histone acetylation and glycolytic inhibition facilitate PGCs formation. The induced PGCs (iPGCs) are transplanted into the recipients, which are self-crossed to produce 189/509 somatic cells derived chicken with the donor's characteristics. Microsatellite analysis and genome sequencing confirm the inheritance of genetic information from the donor. Thus, we demonstrate the feasibility of avian cloning from somatic cells.

LCDM medium supports the derivation of bovine extended pluripotent stem cells with embryonic and extraembryonic potency in bovine-mouse chimeras from iPSCs and bovine fetal fibroblasts

Cattle have emerged as one of the most important domestic animals widely used for meat, milk, and fur. Derivation of bovine pluripotent stem cells (PSCs) can be applied in drug selecting and human disease modeling and facilitated agriculture-related applications such as production of genetically excellent cattle by gene editing. Extended PSCs (EPSCs), capable of differentiating into embryonic and extraembryonic parts, have been generated in mouse, human, and pig. Whether bovine EPSCs could be generated, and their chimeric competency remains unclear. This study focused on derivation of bovine EPSCs using LCDM medium and exploring the characteristics of EPSCs among different species, including bovine, mouse, and human EPSCs. Here, using LCDM medium (consisting of hLIF, CHIR99021, (S)-(+)-dimethindene maleate, and minocycline hydrochloride) enables the derivation of bovine EPSCs from induced PSCs (iPSCs) and bovine fetal fibroblasts (BFF) with stable morphology, pluripotent marker expression, and in vitro differentiation ability. Notably, bovine EPSCs exhibited interspecies chimeric contribution to embryonic and extraembryonic tissues in pre-implantation blastocysts and postimplantation bovine-mouse chimeras. Transcriptome analysis revealed the unique molecular characteristics of bovine EPSCs compared with iPSCs. The similarities and differences in molecular features across bovine, human, and mouse EPSCs were also described by transcriptome analysis. Taken together, the LCDM culture system containing chemical cocktails can be used for the establishment and long-term passaging of bovine EPSCs with embryonic and extraembryonic potency in bovine-mouse chimeras. Our findings lay the foundation of generating PSCs in domestic animals and open avenues for basic and applied research in biology, medicine, and agriculture. DATABASE: Gene expression data of bovine EPSCs and bovine iPSCs are available in the GEO databases under the accession number PRJNA693452.

Perspectives of pluripotent stem cells in livestock

The recent progress in derivation of pluripotent stem cells (PSCs) from farm animals opens new approaches not only for reproduction, genetic engineering, treatment and conservation of these species, but also for screening novel drugs for their efficacy and toxicity, and modelling of human diseases. Initial attempts to derive PSCs from the inner cell mass of blastocyst stages in farm animals were largely unsuccessful as either the cells survived for only a few passages, or lost their cellular potency; indicating that the protocols which allowed the derivation of murine or human embryonic stem (ES) cells were not sufficient to support the maintenance of ES cells from farm animals. This scenario changed by the innovation of induced pluripotency and by the development of the 3 inhibitor culture conditions to support naïve pluripotency in ES cells from livestock species. However, the long-term culture of livestock PSCs while maintaining the full pluripotency is still challenging, and requires further refinements. Here, we review the current achievements in the derivation of PSCs from farm animals, and discuss the potential application areas.

IRF-1 expressed in the inner cell mass of the porcine early blastocyst enhances the pluripotency of induced pluripotent stem cells

BACKGROUND

Despite years of research, porcine-induced pluripotent stem cells (piPSCs) with germline chimeric capacity have not been established. Furthermore, the key transcription factors (TFs) defining the naïve state in piPSCs also remain elusive, even though TFs in the inner cell mass (ICM) are believed to be key molecular determinants of naïve pluripotency. In this study, interferon regulatory factor 1 (IRF-1) was screened to express higher in ICM than trophectoderm (TE). But the impact of IRF-1 on maintenance of pluripotency in piPSCs was not determined.

METHODS

Transcriptome profiles of the early ICM were analyzed to determine highly interconnected TFs. Cells carrying these TFs' reporter were used to as donor cells for somatic cell nuclear transfer to detect expression patterns in blastocysts. Next, IRF1-Flag was overexpressed in DOX-hLIF-2i piPSCs and AP staining, qRT-PCR, and RNA-seq were conducted to examine the effect of IRF-1 on pluripotency. Then, the expression of IRF-1 in DOX-hLIF-2i piPSCs was labeled by GFP and qRT-PCR was conducted to determine the difference between GFP-positive and GFP-negative cells. Next, ChIP-Seq was conducted to identify genes target by IRF-1. Treatment with IL7 in wild-type piPSCs and STAT3 phosphorylation inhibitor in IRF-1 overexpressing piPSCs was conducted to confirm the roles of JAK-STAT3 signaling pathway in IRF-1's regulation of pluripotency. Moreover, during reprogramming, IRF-1 was overexpressed and knocked down to determine the change of reprogramming efficiency.

RESULTS

IRF-1 was screened to be expressed higher in porcine ICM than TE of d6~7 SCNT blastocysts. First, overexpression of IRF-1 in the piPSCs was observed to promote the morphology, AP staining, and expression profiles of pluripotency genes as would be expected when cells approach the naïve state. Genes, KEGG pathways, and GO terms related to the process of differentiation were also downregulated. Next, in the wild-type piPSCs, high-level fluorescence activated by the IRF-1 promoter was associated with higher expression of naïve related genes in piPSCs. Analysis by ChIP-Seq indicated that genes related to the JAK-STAT pathway, and expression of IL7 and STAT3 were activated by IRF-1. The inhibitor of STAT3 phosphorylation was observed could revert the expression of primed genes in IRF-1 overexpressing cells, but the addition of IL7 in culture medium had no apparent change in the cell morphology, AP staining results, or expression of pluripotency related genes. In addition, knockdown of IRF-1 during reprogramming appeared to reduce reprogramming efficiency, whereas overexpression exerted the converse effect.

CONCLUSION

The IRF-1 expressed in the ICM of pigs' early blastocyst enhances the pluripotency of piPSCs, in part through promoting the JAK-STAT pathway.

In-vitro differentiation of early pig spermatogenic cells to haploid germ cells

Spermatogonial stem cells (SSCs) self-renew and contribute genetic information to the next generation. Pig is wildly used as a model animal for understanding reproduction mechanisms of human being. Inducing directional differentiation of porcine SSCs may be an important strategy in exploring the mechanisms of spermatogenesis and developing better treatment methods for male infertility. Here, we established an in-vitro culture model for porcine small seminiferous tubule segments, to induce SSCs to differentiate into single-tail haploid spermatozoa. The culture model subsequently enabled spermatozoa to express the sperm-specific protein acrosin and oocytes to develop to blastocyst stage after round spermatid injection. The addition of retinoic acid (RA) to the differentiation media promoted the efficiency of haploid differentiation. RT-PCR analysis indicated that RA stimulated the expression of Stra8 but reduced the expression of NANOS2 in spermatogonia. Genes involved in post-meiotic development, transition protein 1 (Tnp1) and protamine 1 (Prm1) were upregulated in the presence of RA. The addition of an RA receptor (RAR) inhibitor, BMS439, showed that RA enhanced the expression of cAMP responsive-element binding protein through RAR and promoted the formation of round spermatids. We established an efficient culture system for in-vitro differentiation of pig SSCs. Our study represents a model for human testis disease and toxicology screening. Molecular regulators of SSC differentiation revealed in this study might provide a therapeutic strategy for male infertility.

In vitro breeding: application of embryonic stem cells to animal production†

Embryonic stem cells (ESCs) are derived from the inner cell mass of preimplantation blastocysts. For decades, attempts to efficiently derive ESCs in animal livestock species have been unsuccessful, but this goal has recently been achieved in cattle. Together with the recent reconstitution of the germ cell differentiation processes from ESCs in mice, these achievements open new avenues for the development of promising technologies oriented toward improving health, animal production, and the environment. In this article, we present a strategy that will notably accelerate genetic improvement in livestock populations by reducing the generational interval, namely in vitro breeding (IVB). IVB combines genomic selection, a widely used strategy for genetically improving livestock, with ESC derivation and in vitro differentiation of germ cells from pluripotent stem cells. We also review the most recent findings in the fields on which IVB is based. Evidence suggests this strategy will be soon within reach.

Genome editing approaches to augment livestock breeding programs

The prospect of genome editing offers a number of promising opportunities for livestock breeders. Firstly, these tools can be used in functional genomics to elucidate gene function, and identify causal variants underlying monogenic traits. Secondly, they can be used to precisely introduce useful genetic variation into structured livestock breeding programs. Such variation may include repair of genetic defects, the inactivation of undesired genes, and the moving of useful alleles and haplotypes between breeds in the absence of linkage drag. Editing could also be used to accelerate the rate of genetic progress by enabling the replacement of the germ cell lineage of commercial breeding animals with cells derived from genetically elite lines. In the future, editing may also provide a useful complement to evolving approaches to decrease the length of the generation interval through in vitro generation of gametes. For editing to be adopted, it will need to seamlessly integrate with livestock breeding schemes. This will likely involve introducing edits into multiple elite animals to avoid genetic bottlenecks. It will also require editing of different breeds and lines to maintain genetic diversity, and enable structured cross-breeding. This requirement is at odds with the process-based trigger and event-based regulatory approach that has been proposed for the products of genome editing by several countries. In the absence of regulatory harmony, researchers in some countries will have the ability to use genome editing in food animals, while others will not, resulting in disparate access to these tools, and ultimately the potential for global trade disruptions.

Retinoic acid and/or progesterone differentiate mouse induced pluripotent stem cells into male germ cells in vitro

Numerous reagents were employed for differentiating induced pluripotent stem cells (iPSCs) into male germ cells; however, the induction procedure was ineffective. The aim of this study was to improve the in vitro differentiation of mice iPSCs (miPSCs) into male germ cells with retinoic acid (RA) and progesterone (P). miPSCs were differentiated to embryoid bodies (EBs) in suspension with RA with or without progesterone for 0, 4, and 7 days. Then, the expression of certain genes at different stages of male germ cell development including Ddx4 (pre meiosis), Stra8 (meiosis), AKAP3 (post meiosis), and Mvh protein was examined in RNA and/or protein levels by real-time polymerase chain reaction or flow cytometry, respectively. The Stra8 gene expression increased in the RA groups on all days. But, expression of this gene declined in RA + P groups. In addition, an increased expression of Ddx4 gene was observed on day 0 in the P group. Also, a significant upregulation was observed in the expression of AKAP3 gene in the RA + P group on days 0 and 4. However, gene expression decreased in P and RA groups on day 7. The expression of Mvh protein significantly increased in the RA group on day 7. The Mvh expression was also enhanced in the P group on day 4, but it decreased on day 7, while this protein upregulated on day 0 and 7 in the RA + P group. The miPSCs have the capacity for in vitro differentiation into male germ cells by RA and/or progesterone. However, the effects of these inducers depend on the type of combination and an effective time.

Maternal obesity impairs fetal mitochondriogenesis and brown adipose tissue development partially via upregulation of miR-204-5p

Maternal obesity (MO) predisposes offspring to metabolic disorders, but the mechanisms remain poorly defined. Recent studies emphasize the importance of brown adipose tissue (BAT) in maintaining metabolic health, and MO was recently demonstrated to impair BAT thermogenic function in offspring. The current study aimed to investigate the mechanisms leading to the impairment in fetal BAT development due to MO. Female C57BL/6J mice were fed a control diet or a 60% high-fat diet for 10 weeks, mated and maintained on their respective diets during pregnancy. Fetal tissue was collected at E18.5, the late stage of pregnancy. Fetal BAT contained more triglycerides compared to the control, which was correlated with higher expression of white adipogenic markers. On the other hand, the expression of BAT markers was down-regulated in the MO fetal BAT. Based on RNA-sequencing analyses, genes related to mitochondriogenesis and myogenesis were found to be down-regulated, while those related to white adipocyte differentiation were up-regulated in MO fetal BAT. Because brown adipocytes are derived from myogenic progenitors, the down-regulation of myogenic genes might partially explain hampered brown adipogenesis in MO fetal BAT. Consistently, mitochondrial DNA and mitochondrial biogenesis markers were also down-regulated in MO fetal BAT. MicroRNA-sequencing identified that miR-204-5p expression was elevated in MO fetal BAT. This microRNA targeted the 3'-untranslated regions of PGC1α and Sirt1 mRNA to suppress their expression and impair mitochondriogenesis. In summary, MO impaired fetal BAT development through suppressing myogenesis and brown adipogenesis while enhancing white adipogenic commitment, and inhibited mitochondriogenesis partially through enhancing miR-204-5p expression.

Phytanic acid activates PPARα to promote beige adipogenic differentiation of preadipocytes

A better understanding of the mechanisms of beige and brown adipogenesis is needed for developing strategies to prevent and treat obesity and associated metabolic disorders. Phytanic acid (PA) exists in a wide range of foods, especially in milk fat and marine foods, but its effects on obesity and beige adipogenesis remain poorly defined. The objective is to investigate the effects and regulatory mechanisms of PA in the beige adipogenesis. In 3T3-L1 preadipocytes, PA elevated the expression of brown adipogenic markers, suggesting that PA promotes beige adipogenic differentiation in committed adipogenic cells. In uncommitted C3H10T1/2 cells, while PA increased PGC1α expression, it did not increase brown adipogenic regulators PRDM16 or UCP1 expression, suggesting that PA had no significant effects on brown adipocyte commitment. PA also enhanced mitochondrial biogenesis and oxygen consumption. Promotion of both mitochondriogenesis and beige adipogenic differentiation were blocked by using PPARα antagonist or with Pparα knockdown, showing that PA-mediated beige/brown adipogenic differentiation is dependent on PPARα. Additionally, the PA-regulated effect is independent on β3-adrenergic receptor. Taken together, PA promotes beige adipogenic differentiation, but not the commitment of progenitor cells to the brown adipocyte lineage. PPARα is a key mediator during PA-induced beige/brown adipogenic differentiation.

m6A methylation controls pluripotency of porcine induced pluripotent stem cells by targeting SOCS3/JAK2/STAT3 pathway in a YTHDF1/YTHDF2-orchestrated manner

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) hold great promise for regenerative medicine, disease treatment, and organ transplantation. As the ethical issue of human ESCs and similarity of pig in human genome and physiological characteristics, the porcine iPSCs (piPSCs) have become an ideal alternative study model. N⁶-methyladenosine (m⁶A) methylation is the most prevalent modification in eukaryotic mRNAs, regulating the self-renewal and differentiation of pluripotency stem cells. However, the explicit m⁶A-regulating machinery remains controversial. Here, we demonstrate that m⁶A modification and its modulators play a crucial role in mediating piPSCs pluripotency. In brief, loss of METTL3 significantly impairs self-renewal and triggers differentiation of piPSCs by interfering JAK2 and SOCS3 expression, further inactivating JAK2-STAT3 pathway, which then blocks the transcription of KLF4 and SOX2. We identify that both of JAK2 and SOSC3 have m⁶A modification at 3'UTR by m⁶A-seq analysis. Dual-luciferase assay shows that METTL3 regulates JAK2 and SOCS3 expression in an m⁶A-dependent way. RIP-qPCR validates JAK2 and SOCS3 are the targets of YTHDF1 and YTHDF2, respectively. SiMETTL3 induced lower m⁶A levels of JAK2 and SOCS3 lead to the inhibition of YTHDF1-mediated JAK2 translation and the block of YTHDF2-dependent SOCS3 mRNA decay. Subsequently, the altered protein expressions of JAK2 and SOCS3 inhibit JAK2-STAT3 pathway and then the pluripotency of piPSCs. Collectively, our work uncovers the critical role of m⁶A modification and its modulators in regulating piPSCs pluripotency and provides insight into an orchestrated network linking the m⁶A methylation and SOCS3/JAK2/STAT3 pathway in pluripotency regulation.

Revolutionize livestock breeding in the future: an animal embryo-stem cell breeding system in a dish

Meat and milk production needs to increase ~ 70–80% relative to its current levels for satisfying the human needs in 2050. However, it is impossible to achieve such genetic gain by conventional animal breeding systems. Based on recent advances with regard to in vitro induction of germ cell from pluripotent stem cells, herein we propose a novel embryo-stem cell breeding system. Distinct from the conventional breeding system in farm animals that involves selecting and mating individuals, the novel breeding system completes breeding cycles from parental to offspring embryos directly by selecting and mating embryos in a dish. In comparison to the conventional dairy breeding scheme, this system can rapidly achieve 30–40 times more genetic gain by significantly shortening generation interval and enhancing selection intensity. However, several major obstacles must be overcome before we can fully use this system in livestock breeding, which include derivation and mantaince of pluripotent stem cells in domestic animals, as well as in vitro induction of primordial germ cells, and subsequent haploid gametes. Thus, we also discuss the potential efforts needed in solving the obstacles for application this novel system, and elaborate on their groundbreaking potential in livestock breeding. This novel system would provide a revolutionary animal breeding system by offering an unprecedented opportunity for meeting the fast-growing meat and milk demand of humans.

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.

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.

Three-dimensional wet-electrospun poly(lactic acid)/multi-wall carbon nanotubes scaffold induces differentiation of human menstrual blood-derived stem cells into germ-like cells

Infertility caused by the disruption or absence of germ cells is a major and largely incurable medical problem. Germ cells (i.e., sperm or egg) play a key role in the transmission of genetic and epigenetic information across generations. Generation of gametes derived in vitro from stem cells hold promising prospects which could potentially help infertile men and women. Menstrual blood-derived stem cells are a unique stem cell source. Evidence suggests that menstrual blood-derived stem cells exhibit a multi-lineage potential and have attracted extensive attention in regenerative medicine. To maintain the three-dimensional structure of natural extra cellular matrices in vitro, scaffolds can do this favor and mimic a microenvironment for cell proliferation and differentiation. According to previous studies, poly(lactic acid) and multi-wall carbon nanotubes have been introduced as novel and promising biomaterials for the proliferation and differentiation of stem cells. Some cell types have been successfully grown on a matrix containing carbon nanotubes in tissue engineering but there is no report for this material to support stem cells differentiation into germ cells lineage. This study designed a 3D wet-electrospun poly(lactic acid) and poly(lactic acid)/multi-wall carbon nanotubes composite scaffold to compare infiltration, proliferation, and differentiation potential of menstrual blood-derived stem cells toward germ cell lineage with 2D culture. Our primary data revealed that the fabricated scaffold has mechanical and biological suitable qualities for supporting and attachments of stem cells. The differentiated menstrual blood-derived stem cells tracking in scaffolds using scanning electron microscopy confirmed cell attachment, aggregation, and distribution on the porous scaffold. Based on the differentiation assay by RT-PCR analysis, stem cells and germ-like cells markers were expressed in 3D groups as well as 2D one. It seems that poly(lactic acid)/multi-wall carbon nanotubes scaffold-seeded menstrual blood-derived stem cells could be viewed as a novel, safe, and accessible construct for these cells, as they enhance germ-like generation from menstrual blood-derived stem cells.

Differentiation of Mouse Primordial Germ Cells into Functional Oocytes In Vitro

Various complex molecular events in oogenesis cannot be observed in vivo. As a bioengineering technique for female reproductive tissues, in vitro culture systems for female germ cells have been used to analyze oogenesis and preserve germ cells for over 20 years. Recently, we have established a new methodological approach for the culture of primordial germ cells (PGCs) and successfully obtained offspring. Our PGC culture system will be useful to clarify unresolved mechanisms of fertility and sterility from the beginning of mammalian oogenesis, before meiosis. This review summarizes the history of culture methods for mammalian germ cells, our current in vitro system, and future prospects for the culture of germ cells.