ALK Family Inhibitor A83-01 Promotes the Proliferation of Mouse Male Germline Stem Cells (mGSCs) Under Serum- and Feeder-Free Conditions

A83-01 is a selective inhibitor of the TGF-β type I receptor ALK,which inhibits the TGF-β-induced epithelial-to-mesenchymal transition（EMT） via the inhibition of Smad2 phosphorylation.Previous studies have showed that A83-01 promoted somatic cellular reprogramming significantly.Male germline stem cells（mGSCs）,as an alternative resource of pluripotent stem cells derived adult testis,have promising valuable in clinic medicine and regeneration,however,the derivation of mGSCs was complex and difficult.What the role A83-01 plays in promoting the proliferation of mGSCs is still unknown.In this study,combined with A83-01 and knockout serum replacement（KSR） medium,we obtained a relatively feeder-and serum-free system for mGSCs culturing in vitro and the optimal concentration of A83-01 was 0.25 μmol L-1.After continuous culturing,the proliferation efficiency of undifferentiated mGSCs and differentiation capacity of mGSC were examined as well.Results showed that,A83-01 dramatically increased the number of mGSCs and AP positive colonies,and the mitosis index according to the BrdU assay.A83-01 could also increase the expression of pluripotent markers including Oct4,Klf4,Nanog and c-Myc,analyzed byreal-time quantative PCR.mGSCs cultured in the optimal feeder-and serum-free system combined with A83-01 could form embryoid bodies（EBs）,which consisted of three embryonic layers detected by immunofluorescence and RT-PCR.Remarkably,the results demonstrated 0.25 μmol L-1A83-01 could promote the proliferation of mouse mGSC colonies and maintain their undifferentiated status under feeder-and serum-free systems.

GDNF Up-Regulates c-Myc Transcription via the PI3K/Akt Pathway to Promote Dairy Goat Male Germline Stem Cells (mGSC) Proliferation

Studies have demonstrated that regulation of GDNF on male germline stem cells （mGSCs） mainly through Ras/Erk1/2, Src family kinase and PI3K/Akt signaling pathways, but the signaling pathways GDNF-mediated are different when the species and cell lines varied. Whether GDNF regulates self-renewal of mGSCs isolated from livestock has not been reported. Here, we purified mGSCs from dairy goat testis using mixed enzymes and fibronectin. Immunofluoresce staining revealed the cultured dairy mGSCs expressed Vasa, Nanos2, Ngn3, Tert, Dazl, Lin28, Oct4, CD49f, Stra8 and GFRa1, reflecting that these cells were mGSCs phenotype. Then we cultured these dairy goat mGSCs in different concentrations of GDNF （0, 5, 10, or 20 ng mL-1） to optimize the best concentration of GDNF to sustain the dairy goat mGSCs self-renewal, after that the inhibitor of PI3K （LY294002, 10 μmol L-1） was added to the medium which contains the optimal concentration of GDNF we obtained by experiments. The mGSCs cultured in different media were compared through the population doubling time （PDT）, capacity of cell proliferation evaluated by PCNA and BrdU immunofluorescence staining, RT-PCR, QRT-PCR, Western blotting and flow cytometry. Results showed that 10 ng mL-1 was the optimal concentration of GDNF to maintain goat mGSCs self-renewal and GDNF up-regulates c-Myc transcription via the PI3K/Akt pathway to promote goat mGSCs proliferation. This study provides us an efficient model to study the mechanism in mGSCs proliferation and differentiation in goat, and has important implications in unveiling signaling pathways in livestock GSCs.

Dmrt1 regulates the immune response by repressing the TLR4 signaling pathway in goat male germline stem cells

Double sex and mab-3-related transcription factor 1(Dmrt1),which is expressed in goat male germline stem cells(mGSCs)and Sertoli cells,is one of the most conserved transcription factors involved in sex determination.In this study,we highlighted the role of Dmrt1 in balancing the innate immune response in goat mGSCs.Dmrt1 recruited promyelocytic leukemia zinc finger(Plzf),also known as zinc finger and BTB domain-containing protein 16(Zbtb16),to repress the Toll-like receptor 4(TLR4)-dependent inflammatory signaling pathway and nuclear factor(NF)-κB.Knockdown of Dmrt1 in seminiferous tubules resulted in widespread degeneration of germ and somatic cells,while the expression of proinflammatory factors were significantly enhanced.We also demonstrated that Dmrt1 stimulated proliferation of mGSCs,but repressed apoptosis caused by the immune response.Thus,Dmrt1 is sufficient to reduce inflammation in the testes,thereby establishing the stability of spermatogenesis and the testicular microenvironment.

An efficient strategy for generation of transgenic mice by lentiviral transduction of male germline stem cells in vivo

Background： Male germline stem cells（MGSCs） are a subpopulation of germ cells in the testis tissue. MGSCs are capable of differentiation into spermatozoa and thus are perfect targets for genomic manipulation to generate transgenic animals.Method： The present study was to optimize a protocol of production of transgenic mice through transduction of MGSCs in vivo using lentiviral-based vectors. The recombinant lentiviral vectors with either EF-1 or CMV promoter to drive the expression of enhanced green fluorescent protein（e GFP） transgene were injected into seminiferous tubules or inter-tubular space of 7-day-old and 28-day-old mouse testes. At 5 or 6 wk post-surgery, these pre-founders were mated with wild-type C57BL/6J female mice（1.5 to 2.0-month-old）.Results： Sixty-seven percent of F1 generation and 55.56 % of F2 offspring were positive for eG FP transgene under the control of EF-1 promoter via PCR analysis. The transgenic pups were generated in an injection site-and age-independent manner. The expression of transgene was displayed in the progeny derived from lentiviral vector containing CMV promoter to drive transgene, but it was silenced or undetectable in the offspring derived from lentiviral vector with transgene under EF-1 promoter. The methylation level of g DNA in the promoter region of transgene was much higher in the samples derived lentiviral vectors with EF-1 promoter than that with CMV promoter,suggesting e GFP transgene was suppressed by DNA methylation in vivo.Conclusion： This research reported here an effective strategy for generation of transgenic mice through transduction of MGSCs in vivo using lentivirus vectors with specific promoters, and the transgenic offspring were obtained in an injection site-and age-independent manner. This protocol could be applied to other animal species, leading to advancement of animal transgenesis in agricultural and biomedical fields.

Establishment and characterization of immortalized bovine male germline stem cell line

Male germline stem cells （mGSCs） are unique adult germ cells with self-renewal potential and spermatogenesis function in the testis. However, further studies are needed to establish a long-term cultural system of mGSCs in vitro, especially for large animals such as bovine mGSCs. In this study, we first established a stable immortalized bovine male germline stem cell line by transducing Simian virus 40 （SV40） large T antigen. The proliferation of these cells was improved significantly. These cells could express spermatogonial stem cell （SSC）-specific markers, such as PLZF, PGP9.5, VASA, LIN28A, and CD49F, both in the mRNA and protein levels. Additionally, these cells could be differentiated into three germ layer cells to enter meiosis, form colonies, and proliferate in the seminiferous tubules of busulfan-induced infertile mice. The immortalized bovine mGSCs maintain the criteria of mGSCs.

Ovarian stem cells:From basic to clinical applications

The field of reproductive biology has undergone significant developments in the last decade. The notion that there is a fixed reserve pool of oocytes before birth was established by Zuckerman in 1951. However, in 2004, an article published in nature challenged this central dogma of mammalian reproductive biology. Tilly's group reported the existence of ovarian germline stem cells(GSCs) in postnatal ovaries of mice and suggested that the bone marrow could be an extragonadal source of ovarian GSCs. These findings were strongly criticized; however, several independent groups have sincesuccessfully isolated and characterized ovarian GSCs in postnatal mice. The ovarian GSCs are located in the ovarian surface epithelium and express markers of undifferentiated GSCs. When transplanted into mouse ovaries, mouse ovarian GSCs could differentiate and produce embryos and offspring. Similarly, in a recent study, ovarian GSCs were found to be present in the ovaries of women of reproductive age. Conversely, there is increasing evidence that stem cells responsible for maintaining a healthy state in normal tissue may be a source of some cancers, including ovarian cancer. Cancer stem cells(CSCs) have been found in many tissues, including ovaries. Some researchers have suggested that ovarian cancer may be a result of the transformation and dysfunction of ovarian GSCs with self-renewal properties. Drug resistant and metastasisgenerating CSCs are responsible for many important problems affecting ovarian cancer patients. Therefore, the identification of CSCs will provide opportunities for the development of new therapeutic strategies for treatments for infertility and ovarian cancer. In this article, we summarize the current understanding of ovarian GSCs in adult mammals, and we also discuss whether there is a relationship between GSCs and CSCs.

Induced pluripotent stem cells: Mechanisms, achievements and perspectives in farm animals

Pluripotent stem cells are unspecialized cells withunlimited self-renewal, and they can be triggered to differentiate into desired specialized cell types. These features provide the basis for an unlimited cell source for innovative cell therapies. Pluripotent cells also allow to study developmental pathways, and to employ them or their differentiated cell derivatives in pharmaceutical testing and biotechnological applications. Via blastocyst complementation, pluripotent cells are a favoured tool for the generation of genetically modified mice. The recently established technology to generate an induced pluripotency status by ectopic co-expression of the transcription factors Oct4, Sox2, Klf4 and c-Myc allows to extending these applications to farm animal species, for which the derivation of genuine embryonic stem cells was not successful so far. Most induced pluripotent stem(i PS) cells are generated by retroviral or lentiviral transduction of reprogramming factors. Multiple viral integrations into the genome may cause insertional mutagenesis and may increase the risk of tumour formation. Non-integration methods have been reported to overcome the safety concerns associated with retro and lentiviral-derived i PS cells, such as transient expression of the reprogramming factors using episomal plasmids, and direct delivery of reprogramming m RNAs or proteins. In this review, we focus on the mechanisms of cellular reprogramming and current methods used to induce pluripotency. We also highlight problems associated with the generation of i PS cells. An increased understanding of the fundamental mechanisms underlying pluripotency and refining the methodology of i PS cell generation will have a profound impact on future development and application in regenerative medicine and reproductive biotechnology of farm animals.

Manipulation of spermatogonial stem cells in livestock species

We are entering an exciting epoch in livestock biotechnology during which the fundamental approaches(such as transgenesis, spermatozoa cryopreservation and artificial insemination) will be enhanced based on the modern understanding of the biology of spermatogonial stem cells(SSCs) combined with the outstanding recent advances in genomic editing technologies and in vitro cell culture systems. The general aim of this review is to outline comprehensively the promising applications of SSC manipulation that could in the nearest future find practical application in livestock breeding. Here, we will focus on 1) the basics of mammalian SSC biology;2) the approaches for SSC isolation and purification;3) the available in vitro systems for the stable expansion of isolated SSCs;4) a discussion of how the manipulation of SSCs can accelerate livestock transgenesis;5) a thorough overview of the techniques of SSC transplantation in livestock species(including the preparation of recipients for SSC transplantation,the ultrasonographic-guided SSC transplantation technique in large farm animals, and the perspectives to improve further the SSC transplantation efficiency), and finally, 6) why SSC transplantation is valuable to extend the techniques of spermatozoa cryopreservation and/or artificial insemination. For situations where no reliable data have yet been obtained for a particular livestock species, we will rely on the data obtained from studies conducted in rodents because the knowledge gained from rodent research is translatable to livestock species to a great extent. On the other hand, we will draw special attention to situations where such translation is not possible.

Germline competence of mouse ES and iPS cell lines: Chimera technologies and genetic background

In mice,gene targeting by homologous recombination continues to play an essential role in the understanding of functional genomics.This strategy allows precise location of the site of transgene integration and is most commonly used to ablate gene expression("knock-out"),or to introduce mutant or modified alleles at the locus of interest("knock-in").The efficacy of producing live,transgenic mice challenges our understanding of this complex process,and of the factors which influence germline competence of embryonic stem cell lines.Increasingly,evidence indicates that culture conditions and in vitro manipulation can affect the germline-competence of Embryonic Stem cell(ES cell) lines by accumulation of chromosome abnormalities and/or epigenetic alterations of the ES cell genome. The effectiveness of ES cell derivation is greatly strain-dependent and it may also influence the germline transmission capability.Recent technical improvements in the production of germline chimeras have been focused on means of generating ES cells lines with a higher germline potential.There are a number of options for generating chimeras from ES cells (ES chimera mice);however,each method has its advantages and disadvantages.Recent developments in induced pluripotent stem(iPS)cell technology have opened new avenues for generation of animals from genetically modified somatic cells by means of chimera technologies.The aim of this review is to give a brief account of how the factors mentioned above are influencing the germline transmission capacity and the developmental potential of mouse pluripotent stem cell lines.The most recent methods for generating specifically ES and iPS chimera mice,including the advantages and disadvantages of each method are also discussed.

Stem cells of the reproductive tract of women

Research in stem cells is one of the most rapidly evolving fields of investigation in medicine today. Stem cells are defined as cells that have the capacity to both generate daughter cells identical to the cell of origin (self-renewal) and to produce progeny with more restricted, specialized potential (differentiated cells). This dual ability to self-renew and differentiate offers great promise for expanding our understanding of organ systems, elucidating disease pathophysiology, and creating therapeutic approaches to difficult diseases. The goal of this review is to offer an overview of the different types of stem cells and to provide an introduction to the applications of stem cells to the field of obstetrics and gynecology.

The Drosophila ovary: an active stem cell community

Only a small number of cells in adult tissues （the stem cells） possess the ability to self-renew at every cell division, while producing differentiating daughter cells to maintain tissue homeostasis for an organism＇s lifetime. The Drosophila ovary harbors three different types of stem cell populations （germline stem cell （GSC）, somatic stem cell （SSC） and escort stem cell （ESC）） located in a simple anatomical structure known as germarium, rendering it one of the best model systems for studying stem cell biology due to reliable stem cell identification and available sophisticated genetic tools for manipulating gene functions. Particularly, the niche for the GSC is among the first and best studied ones, and studies on the GSC and its niche have made many unique contributions to a better understanding of relationships between stem cells and their niche. So far, both the GSC and the SSC have been shown to be regulated by extrinsic factors originating from their niche and intrinsic factors functioning within. Multiple signaling pathways are required for controlling GSC and SSC self-renewal and differentiation, which provide unique opportunities to investigate how multiple signals from the niche are interpreted in the stem cell. Since the Drosophila ovary contains three types of stem cells, it also provides outstanding opportunities to study how multiple stem cells in a given tissue work collaboratively to contribute to tissue function and maintenance. This review highlights recent major advances in studying Drosophila ovarian stem cells and also discusses future directions and challenges.

Stem cell autotomy and niche interaction in different systems

The best known cases of cell autotomy are the formation of erythrocytes and thrombocytes(platelets) from progenitor cells that reside in special niches. Recently, autotomy of stem cells and its enigmatic interaction with the niche has been reported from male germline stem cells(GSCs) in several insect species. First described in lepidopterans, the silkmoth, followed by the gipsy moth and consecutively in hemipterans, foremost the milkweed bug. In both, moths and the milkweed bug, GSCs form finger-like projections toward the niche, the apical cells(homologs of the hub cells in Drosophila). Whereas in the milkweed bug the projection terminals remain at the surface of the niche cells, in the gipsy moth they protrude deeply into the singular niche cell. In both cases, the projections undergo serial retrograde fragmentation with progressing signs of autophagy. In the gipsy moth, the autotomized vesicles are phagocytized and digested by the niche cell. In the milkweed bug the autotomized vesicles accumulate at the niche surface and disintegrate. Autotomy and sprouting of new projections appears to occur continuously. The significance of the GSC-niche interactions, however, remains enigmatic. Our concept on the signaling relationship between stem cell-niche in general and GSC and niche(hub cells and cyst stem cells) in particular has been greatly shaped by Drosophila melanogaster. In comparing the interactions of GSCs with their niche in Drosophila with those in species exhibiting GSC autotomy it is obvious that additional or alternative modes of stem cell-niche communication exist. Thus, essential signaling pathways, including niche-stem cell adhesion(E-cadherin) and the direction of asymmetrical GSC division- as they were found in Drosophila- can hardly be translated into the systems where GSC autotomywas reported. It is shown here that the serial autotomy of GSC projections shows remarkable similarities with Wallerian axonal destruction, developmental axon pruning and dying-back degeneration in neurodegenerative diseases. Especially the hypothesis of an existing evolutionary conserved "autodestruction program" in axons that might also be active in GSC projections appears attractive. Investigations on the underlying signaling pathways have to be carried out. There are two other well known cases of programmed cell autotomy: the enucleation of erythroblasts in the process of erythrocyte maturation and the segregation of thousands of thrombocytes(platelets) from one megakaryocyte. Both progenitor cell types- erythroblasts and megakaryocytes- are associated with a niche in the bone marrow, erythroblasts with a macrophage, which they surround, and the megakaryocytes with the endothelial cells of sinusoids and their extracellular matrix. Although the regulatory mechanisms may be specific in each case, there is one aspect that connects all described processes of programmed cell autotomy and neuronal autodestruction: apoptotic pathways play always a prominent role. Studies on the role of male GSC autotomy in stem cell-niche interaction have just started but are expected to reveal hitherto unknown ways of signal exchange. Spermatogenesis in mammals advance our understanding of insect spermatogenesis. Mammal and insect spermatogenesis share some broad principles, but a comparison of the signaling pathways is difficult. We have intimate knowledge from Drosophila, but of almost no other insect, and we have only limited knowledge from mammals. The discovery of stem cell autotomy as part of the interaction with the niche promises new general insights into the complicated stem cell-niche interdependence.

CD39介导GSCs抵抗辐射诱导ICD的初步探究

脑胶质瘤干细胞(glioma stem cells,GSCs)的辐射抗性造成放疗后脑胶质瘤复发率高,CD39介导GSCs抵抗辐射诱导的免疫原性细胞死亡(immunogenic cell death,ICD)可能是放疗耐受的重要原因。目的:深入阐释CD39介导GSCs抵抗辐射诱导ICD的分子机制。方法:免疫荧光染色法和流式细胞术检测GSCs干性标记物、ICD标记物、抑制CD39后胞外ATP变化、ATP对DCs炎症小体激活以及吞噬功能的影响。利用Western blot和流式细胞术检测HIF-1α与CD39相关性。利用流式细胞术检测抑制CD39后激活T淋巴细胞的增殖分化和杀伤效应。结果:GSCs的ICD标记物分子普遍低表达,通过膜表面CD39水解胞外ATP,维持免疫抑制微环境。抑制CD39则阻断ATP水解,显著增强“吃我”信号,吸引树突状细胞(dendritic cells,DCs)聚集。ATP激活DCs的P2X7受体,从而激活NF-κB p65-NLRP3-Caspase-1 p20-IL-1β炎症小体信号通路,促进pro-IL-1β转向成熟的IL-1β释放,引发炎症反应。DCs也向T细胞递呈抗原增加,MHC分子表达水平上调,最终激活淋巴细胞杀伤效应。结论:抑制CD39表达能明显增强辐射诱导的肿瘤细胞ICD,通过激活NF-κB p65-NLRP3-Caspase-1 p20-IL-1β信号通路,促进淋巴细胞免疫反应。

Conversion of female germline stem cells from neonatal and prepubertal mice into pluripotent stern cells

Pluripotent stem cells derived from neonatal or adult testes are a useful tool to examine the mechanisms of pluripotency and a resource for cell-based therapies. However, therapies usingthese cells will only benefit males but not females. Recently, female germline stem cells （FGSCs） were discovered in ovaries. Whether FGSCs can be converted into pluripotent stem cells, similar to spermatogonial stem cells, is unknown. Here, we demonstrate that female embryonic stem-like cells （fESLCs） can be generated within 1 month from the stably proliferating FGSCs cultured in embryonic stem cell （ESC） medium, fESLCs exhibit properties similar to those of ESCs in terms of marker expression and differentiation potential. Thus, our findings suggest that generation of patient-specific fESLCs is feasible and provides a foundation for personalized regenerative applications.

Hsp83 regulates the fate of germline stem cells in Drosophila ovary

In adult tissues,stem cells are defined by their unique capacity to self-renew and produce differentiated cells to maintain tissue homeostasis.Drosophila ovarian germline stem cells（GSCs）provide a powerful model for investigating the regulatory mechanisms underlying stem cell fate determination in vivo（Chen and Mckearin.

Production of transgenic mice by random recombination of targeted genes in female germline stem cells

Oocyte production in most mammalian species is believed to cease before birth.However,this idea has been challenged with the finding that postnatal mouse ovaries possess mitotically active germ cells.A recent study showed that female germline stem cells(FGSCs)from adult mice were isolated,cultured long term and produced oocytes and progeny after transplantation into infertile mice.Here,we demonstrate the successful generation of transgenic or gene knock-down mice using FGSCs.The FGSCs from ovaries of 5-day-old and adult mice were isolated and either infected with recombinant viruses carrying green fluorescent protein,Oocyte-G1 or the mouse dynein axonemal intermediate chain 2 gene,or transfected with the Oocyte-G1 specific shRNA expression vector(pRS shOocyte-G1 vector),and then transplanted into infertile mice.Transplanted cells in the ovaries underwent oogenesis and produced heterozygous offspring after mating with wild-type male mice.The offspring were genetically characterized and the biological functions of the transferred or knock-down genes were investigated.Efficiency of genetransfer or gene knock-down was 29%–37%and it took 2 months to produce transgenic offspring.Gene manipulation of FGSCs is a rapid and efficient method of animal transgenesis and may serve as a powerful tool for biomedical science and biotechnology.

Germline-competent stem cell in avian species and its application

Germ cells are the only cell type in the body that can transfer genetic information to the next generation. Germline-competent stem cells can self-renew and contribute to the germ cell lineage giving rise to pluripotent stem cells under specific conditions. Hence far, studies on germline-competent stem cells have contributed to,the generation of avian model systems and the conservation of avian genetic resources. In this review, we focus on previous studies on germline-competent stem cells from avian species, mainly chicken germline-competent stem cells, which have been well established and characterized. We discuss different sources of germline-competent stem cells and recent advances for the future applications in birds.

基于PI3K/AKT通路探讨左归丸改善卵巢衰老大鼠卵巢生殖干细胞干性的机制

目的基于磷脂酰肌醇3激酶/蛋白激酶B(PI3K/AKT)通路探讨左归丸通过缝隙连接蛋白43(Cx43)磷酸化改善卵巢衰老大鼠卵巢生殖干细胞(OSCs)干性的机制。方法将8周龄雌性SD大鼠随机分为正常组、模型组、脱氢表雄酮(DHEA)组、左归丸组,每组6只。采用环磷酰胺腹腔注射15 d复制卵巢衰老大鼠模型。模型复制结束后,DHEA组大鼠灌胃DHEA 8.1 mg·kg^(-1),左归丸组大鼠灌胃左归丸1.85 g·kg^(-1),每日1次,连续30 d。采用HE染色法观察大鼠卵巢组织病理变化及各级卵泡计数;ELISA法检测大鼠血清抗缪勒管激素(AMH)、卵泡刺激素(FSH)、雌二醇(E_(2))水平;Western Blot法检测卵巢组织中相关蛋白(PCNA、MVH、Oct4、Cx43、p-Cx43、EGFR、AKT、p-AKT)的表达水平。结果与正常组比较,模型组大鼠体质量明显下降(P<0.05),卵巢湿质量明显降低(P<0.05),始基卵泡数显著减少(P<0.01);血清FSH水平显著升高(P<0.01),E_(2)、AMH水平呈下降趋势(P>0.05);卵巢组织中Oct4、MVH、PCNA、EGFR、p-AKT/AKT、p-Cx43(Ser368)/Cx43、Cx43蛋白表达水平均明显降低(P<0.05,P<0.01)。与模型组比较,左归丸组大鼠体质量明显升高(P<0.05),卵巢湿质量、卵巢指数均显著升高(P<0.01),始基卵泡数显著增加(P<0.01);血清E2水平明显升高(P<0.05);卵巢组织中Oct4、MVH、PCNA、EGFR、p-AKT/AKT、p-Cx43(Ser368)/Cx43、Cx43蛋白水平表达均显著升高(P<0.05,P<0.01)。结论左归丸可能通过维持OSCs干性改善卵巢衰老,其作用机制与PI3K/AKT信号通路及缝隙连接蛋白磷酸化相关。

精原干细胞自我更新及分化的调控机制研究进展

精原干细胞(SSC)是睾丸中最原始的生殖细胞,通过自我更新和连续分化最终成为成熟的精子,SSC对维持高效的精子发生起着至关重要的作用,与生精微环境(niche)之间复杂的分子和细胞相互作用构成了精子发生的基础。以往认为niche主要由睾丸支持细胞构成,而新近研究表明,睾丸内多种细胞、分子信号通路均参与调控SSC的自我更新及分化。本文就睾丸生精微环境调控SSC自我更新及分化的研究进展进行综述。

Recent advances in isolation,identification,and culture of mammalian spermatogonial stem cells

Continuous spermatogenesis depends on the self-renewal and differentiation of spermatogonial stem cells(SSCs).SSCs,the only male reproductive stem cells that transmit genetic material to subsequent generations,possess an inherent self-renewal ability,which allows the maintenance of a steady stem cell pool.SSCs eventually differentiate to produce sperm.However,in an in vitro culture system,SSCs can be induced to differentiate into various types of germ cells.Rodent SSCs are well defined,and a culture system has been successfully established for them.In contrast,available information on the biomolecular markers and a culture system for livestock SSCs is limited.This review summarizes the existing knowledge and research progress regarding mammalian SSCs to determine the mammalian spermatogenic process,the biology and niche of SSCs,the isolation and culture systems of SSCs,and the biomolecular markers and identification of SSCs.This information can be used for the effective utilization of SSCs in reproductive technologies for large livestock animals,enhancement of human male fertility,reproductive medicine,and protection of endangered species.