原始卵泡的形成与发育

在胚胎发育时期,原始生殖细胞形成并迁移至生殖腺,形成种系囊。卵原细胞进入减数分裂成为卵母细胞。随后种系囊分裂,单个卵母细胞与前颗粒细胞组装成原始卵泡。前泡膜细胞被募集到原始卵泡周围,原始卵泡发育并向初级卵泡转化。原始卵泡的形成和发育是卵巢生物学的重要过程,阐释其分子和细胞机制为调节卵巢功能和治疗卵巢疾病提供方向。     

Generation of male germ cells from induced pluripotent stem cells (iPS cells): an in vitro and in vivo study

Recent studies have reported that induced pluripotent stem (iPS) cells from mice and humans can differentiate into primordial germ cells. However, whether iPS cells are capable of producing male germ cells is not known. The objective of this study was to investigate the differentiation potential of mouse iPS cells into spermatogonial stem cells and late-stage male germ cells. We used an approach that combines in vitro differentiation and in vivo transplantation. Embryoid bodies (EBs) were obtained from iPS cells using leukaemia inhibitor factor (LIF)-free medium. Quantitative PCR revealed a decrease in Oct4 expression and an increase in Stra8 and Vasa mRNA in the EBs derived from iPS cells. iPS cell-derived EBs were induced by retinoic acid to differentiate into spermatogonial stem cells (SSCs), as evidenced by their expression of VASA, as well as CDH1 and GFRα1, which are markers of SSCs. Furthermore, these germ cells derived from iPS cells were transplanted into recipient testes of mice that had been pre-treated with busulfan. Notably, iPS cell-derived SSCs were able to differentiate into male germ cells ranging from spermatogonia to round spermatids, as shown by VASA and SCP3 expression. This study demonstrates that iPS cells have the potential to differentiate into late-stage male germ cells. The derivation of male germ cells from iPS cells has potential applications in the treatment of male infertility and provides a model for uncovering the molecular mechanisms underlying male germ cell development.     

From embryonic stem cells to testicular germ cell cancer-- should we be concerned?

Since the discovery of testicular carcinoma in situ (CIS) -- the precursor cell for the vast majority of germ cell tumours -- it has been proposed that CIS cells could be derived from transformed primordial germ cells or gonocytes. Here, we review recent discoveries not only substantiating that initial hypothesis but also indicating that CIS cells have a striking phenotypic similarity to embryonic stem cells (ESC). Many cancers have been proposed to originate from tissue-specific stem cells [so-called 'cancer stem cells' (CSC)] and we argue that CIS may be a very good example of a CSC, but with exceptional features due to the retention of embryonic pluripotency. In addition, considering the fact that pre-invasive CIS cells are transformed from early fetal cells, possibly due to environmentally induced alterations of the niche, we discuss potential risks linked to the uncontrolled therapeutic use of ESC.     

干细胞向雄性配子诱导分化研究进展

人类雄性配子的重要功能之一是完整地将父代遗传信息传递给子代。配子发生,尤其雄性配子发生是个极其复杂的细胞分化过程,它包括有丝分裂与减数分裂两大过程。然而由于缺乏可重复、高效率研究雄性配子发生的体外培养体系,生殖细胞发生、发育机制研究进展缓慢。干细胞经体外诱导向雄性生殖细胞分化的研究,将推进生殖细胞发育研究,甚至生殖生物学的发展。本文综述近年原始生殖细胞体外培养及干细胞向雄性配子诱导分化的研究进展。     

小鼠iPS细胞具备诱导性原始生殖细胞分化潜能的研究

目的:探讨小鼠诱导性多能干细胞IP14D-1是否具备诱导性原始生殖细胞(induced primordial germcells,iPGCs)分化潜能,以及特异基因表达变化及可能机制。方法:未分化IP14D-1培养扩增,分化形成诱导性拟胚体(induced embryoid bodies,iEBs)。RT-PCR和免疫荧光分别检测4、7、9 d的iEBs中Lin28、Blimp1、Stra8和Mvh的表达变化和蛋白定位情况。结果:未分化IP14D-1同小鼠胚胎干细胞(mouse embryonic stem cells,mESCs)相同,Lin28表达较弱,Blimp1表达相对较强,Mvh和Stra8也在这两种细胞及其相应iEBs和EBs中表达,但均无明显差别。IP14D-1分化形成的iEBs从4 d生长到7 d时,Lin28表达逐渐增强,到9 d时表现为下降,Blimp1表达则随着iEB生长时间延长而逐渐降低。结论:建立了IP14D-1和相应拟胚体(iEBs)的完善、稳定的培养及分化体系;未分化IP14D-1与mESCs在Lin28、Blimp1、Mvh和Stra8表达方面无明显差别;iEB和EBs的Mvh和Stra8表达也无明显差别。IP14D-1及iEBs具有iPGCs分化潜能,且可能是7 d的iEBs内iPGCs分化数量较多,之后进入iPGCs分化的Lin28低表达时期。     

Spermatogonial stem cells: progress and prospects

Twenty years ago, the transplantation of spermatogonial stem cells (SSCs) from a mouse to other recipient mice was shown to be feasible, which clearly demonstrated the functional identity of SSCs. Since then, several important new findings and other technical developments have followed, which included a new hypothesis on their cell kinetics and spermatogonial hierarchy in the testis, a culture method allowing their self-renewal and proliferation, a testis tissue organ culture method, which induced their complete differentiation up to sperm, and the in vitro induction of germ cells from embryonic stem cells and induced pluripotent stem cells. These advancements reinforced or advanced our understanding of this unique cell. Nonetheless, there are many unresolved questions in the study of spermatogonial stem cells and a long road remains until these cells can be used clinically in reproductive medicine.     

Application of three-dimensional culture systems to study mammalian spermatogenesis,with an emphasis on the rhesus monkey (Macaca mulatta)

In vitro culture of spermatogonial stem cells (SSCs) has generally been performed using two-dimensional (2D) culture systems; however, such cultures have not led to the development of complete spermatogenesis. It seems that 2D systems do not replicate optimal conditions of the seminiferous tubules (including those generated by the SSC niche) and necessary for spermatogenesis. Recently, one of our laboratories has been able to induce proliferation and differentiation of mouse testicular germ cells to meiotic and postmeiotic stages including generation of sperm in a 3D soft agar culture system (SACS) and a 3D methylcellulose culture system (MCS). It was suggested that SACS and MCS form a special 3D microenvironment that mimics germ cell niche formation in the seminiferous tubules, and thus permits mouse spermatogenesis in vitro. In this review, we (1) provide a brief overview of the differences in spermatogenesis in rodents and primates, (2) summarize data related to attempts to generate sperm in vitro, (3) report for the first time formation of colonies/clusters of cells and differentiation of meiotic (expression of CREM-1) and postmeiotic (expression of acrosin) germ cells from undifferentiated spermatogonia isolated from the testis of prepubertal rhesus monkeys and cultured in SACS and MCS, and (4) indicate research needed to optimize 3D systems for in vitro primate spermatogenesis and for possible future application to man.     

Regulation of Initiation of Meiosis in Fetal Gonads

Undifferentiated 11 day old fetal mouse gonads were cultured for 7 days in media in which tissues of fetal mouse testis or rete testis had grown. The rete testis medium contained a substance, which triggers the male germ cells to enter meiosis. The medium from the testis blocked meiosis in the female germ cells. It is proposed that a meiosis inducing substance. MIS, and a meiosis preventing substance, MPS, are present within the differentiating fetal testis, and that the two substances participate in the control of germ cell behaviour.     

Culture adaptation of embryonic stem cells echoes germ cell malignancy

Teratocarcinomas are a subset of tumours that result from the neoplastic transformation of primordial germ cells. Such germ cell tumours (GCT) are histologically heterogeneous, reflecting a capacity for differentiation (pluripotency) of their embryonal carcinoma (EC) stem cells. However, malignant evolution of these tumours may ultimately correlate with a decrease in pluripotency, because this would tend to increase the propensity of EC cells for self-renewal. Human embryonic stem (ES) cells, derived from early blastocysts, closely resemble EC cells and, on prolonged culture in vitro, acquire progressive genetic changes that show striking similarity to those seen in GCT (e.g. gain of material from chromosome 12). In parallel, these abnormal ES cells show enhanced population growth rates and plating efficiencies, indicative of their adaptation to culture conditions. Understanding the mechanisms that drive such culture adaptation of ES cells may also provide insights into the development and progression of GCT.     

Can we grow sperm？ A translational perspective on the current animal and human spermatogenesis models

There have been tremendous advances in both the diagnosis and treatment of male factor infertility; however, the mechanisms responsible to recreate spermatogenesis outside of the testicular environment continue to elude andrologists. Having the ability to ‘grow'' human sperm would be a tremendous advance in reproductive biology with multiple possible clinical applications, such as a treatment option for men with testicular failure and azoospermia of multiple etiologies. To understand the complexities of human spermatogenesis in a research environment, model systems have been designed with the intent to replicate the testicular microenvironment. Currently, there are both in vivo and in vitro model systems. In vivo model systems involve the transplantation of either spermatogonial stem cells or testicular xenographs. In vitro model systems involve the use of pluripotent stem cells and complex coculturing and/or three-dimensional culturing techniques. This review discusses the basic methodologies, possible clinical applications, benefits and limitations of each model system. Although these model systems have greatly improved our understanding of human spermatogenesis, we unfortunately have not been successful in demonstrating complete human spermatogenesis outside of the testicle.     

In vitro isolation of stem cells derived from human dental pulp

Agha‐Hosseini F, Jahani M‐A, Jahani M, Mirzaii‐Dizgah I, Ali‐Moghaddam K. In vitro isolation of stem cells derived from human dental pulp.
Clin Transplant 2009: DOI: 10.1111/j.1399‐0012.2009.01137.x.
© 2009 John Wiley & Sons A/S. Abstract: Stem cells are characterized by the ability to differentiate and to self‐renew. Stem cells derived from human dental pulp have been shown to differentiate into osteoblasts serving as a potential source of autologous bone produced in vitro. The purpose of the present study was to isolate mesenchymal stem cells from dental pulp. Dental pulp was gently extracted from 27 intact human permanent third molars of patients aged 18–25. Cow horn forceps were used to isolate intact dental pulp in sterilized condition. The pulps were cultured in a medium containing Dulbecco’s modified Eagle’s medium‐low glucose (DMEM)‐LG and Amphotericin 1%. The cells were subsequently expanded by passages, two passages were performed before they were stored in liquid nitrogen for further examination. DMEM + fetal bovine serum (FBS) 10% L‐Glutamin 0.1% + Trypsin 2.5% + ethylene diamine tetraacetic acid (EDTA) were used for passage. Light microscope and flow cytometry were used to study the cells. The isolated dental pulp cells expressed mesenchymal stem cell markers. The cells were negative for CD34 and CD31 and CD45 but were positive for CD13, CD44, CD90, CD166, and CD105. These results indicate that dental pulp can be use as a source of stem cells that we can isolate and culture.     

Current knowledge of risk factors for testicular germ cell tumors

The development of the human gonads is tightly regulated by the correct sequential expression of many genes and hormonal activity. Disturbance of this regulation does not only prevent proper development of the gonads, but it also contributes to the development of testicular germ cell tumors. Recent genetic studies, especially genome‐wide association studies, have made great progress in understanding genetic susceptibility. Although there is strong evidence of inherited risks, many environmental factors also contribute to the development of testicular germ cell tumors. Histopathological studies have shown that most testicular germ cell tumors arise from germ cell neoplasia in situ, which is thought to be arrested and transformed primordial germ cells. Seminoma has features identical to germ cell neoplasia in situ or primordial germ cells, whereas non‐seminoma shows varied differentiation. Seminomas and embryonic cell carcinomas have the feature of pluripotency, which is thought to be the cause of histological heterogeneity and mixed pathology in testicular germ cell tumors. Testicular germ cell tumors show high sensitivity to chemotherapies, but 20–30% of patients show resistance to standard chemotherapy. In the present review, the current knowledge of the epidemiological and genomic factors for the development of testicular germ cell tumors is reviewed, and the mechanisms of resistance to chemotherapies are briefly mentioned.     

Nestin expression in central nervous system germ cell tumors

Central nervous system (CNS) germ cell tumors constitute a unique class of rare tumors that mainly affect children and adolescents. These tumors are believed to originate from displaced primordial germ cells. Recently, results of treatment of germ cell tumors have improved with use of radiotherapy and combination chemotherapy. However, some tumors have proven refractory to intensive treatment with surgery, radiation, and combination chemotherapy. Nestin is an intermediate filament protein expressed in undifferentiated cells during CNS development and in CNS tumors and is used as a marker of immature elements of tumors, including brain tumor stem cells. In this study, we examined for the first time nestin expression in 19 CNS germ cell tumors (nine pure germinomas, five germinomas with syncytiotrophoblastic giant cells, one yolk sac tumor, one choriocarcinoma, one embryonal carcinoma, and two mature teratomas). Nestin was expressed in 14 cases but was not expressed in three pure germinomas and two mature teratomas. Clinically, nestin-negative tumors did not exhibit dissemination, while all tumors that exhibited dissemination also strongly expressed nestin protein. These findings suggest that the detection of nestin expression could be useful in the management of CNS germ cell tumors, as an auxiliary predictor of dissemination and/or progression.     

人精原干细胞的体外培养及其功能鉴定

目的:通过应用多种培养条件下的生殖细胞共培养体系,寻求人精原干细胞(SSC)长期体外生存和扩增的优化途径。方法:应用磁式分选所获得的α6+Thy-1+c-k it-细胞,分别以STO、MEF、Sertoli细胞为饲养层,于DMEM/F12、DMEM或DMEM-SF培养液条件下短期培养,然后选择胎儿Sertoli细胞作为共培养体系,在32℃、5%CO2、DMEM/F12(含10%胎牛血清)培养条件下,分别观察成人和胎儿生殖细胞的长期培养结果。并应用免疫组化技术和SSC移植技术对培养细胞进行初步生物学特性和功能鉴定。结果:在短期培养中,α6+Thy-1+c-k it-细胞在存在饲养层时,可在DMEM和DMEM/F12培养液中稳定生存,1周内存活率可达90%。长期培养条件下,α6+Thy-1+c-k it-细胞逐渐与Sertoli细胞形成紧密的贴附或镶嵌关系,呈单个、成对、短链状或小团簇状;胎儿SSC与成人类似,部分以圆球形散在分布于Sertoli细胞表面,并常可观察到明显的成对或短链状细胞,部分呈有突起的长梭形扁平细胞,与Sertoli细胞相互形成紧密连接;经反复传代3个月,仍可观察到稳定存在的圆球形SSC贴附于Ser-toli细胞表面。由PKH26标记的α6+Thy-1+c-k it-细胞在移植后2个月可迁移至裸鼠生精小管基膜,表现为单个或成对的细胞。生精小管内荧光细胞计数显示α6+Thy-1+c-k it-细胞在体外培养2、4周后仍然保留54.9%和9.2%的SSC。结论:该培养系统的进一步优化将有利于体外产生大量SSC,并有助于进一步深入了解SSC的生物学特性和男性生精功能障碍的治疗。     

Survival of Mammary Stem Cells in Suspension Culture: Implications for Stem Cell Biology and Neoplasia

There is increasing evidence that a variety of neoplasms including breast cancer may result from transformation of normal stem and progenitor cells. In the past, isolation and characterization of mammary stem cells has been limited by the lack of suitable culture systems able to maintain these cells in an undifferentiated state in vitro. We have recently described a culture system in which human mammary stem and progenitor cells are able to survive in suspension and produce spherical colonies composed of both stem and progenitor cells. Recent observation that adult stem cells from other tissues may also retain the capacity for growth under anchorage independent conditions suggests a common underlying mechanism. We propose that this mechanism involves the interaction between the canonical Wnt signal pathway and E-cadherin. The Wnt pathway has been implicated in normal stem cell self-renewal in vivo. Furthermore, there is evidence that deregulation of this pathway in the mammary gland and other organs may play a key role in carcinogenesis. Thus, the development of in vitro suspension culture systems not only provides an important new tool for the study of mammary cell biology, but also may have important implications for understanding key molecular pathways in both normal and neoplastic stem cells.     

Dysfunction of the mitotic:meiotic switch as a potential cause of neoplastic conversion of primordial germ cells

Germ cell tumours (GCT) are thought to arise as the result of a defect in early development, probably shortly after arrival of the migrating primordial germ cells (PGC) in the genital ridge when, if in a male genital ridge, the germ cells arrest in mitosis, but in a female genital ridge they enter meiosis. We suggest that dysfunction of the mitotic:meiotic switch, with cells aberrantly co-expressing functions pertinent to both states, might provide the genetic instability that could initiate tumour development. If this hypothesis is correct, GCT could arise because of disruption in the function of any one of a number of different genes involved in controlling mitosis and meiosis, rather than being dependent upon a single prominent susceptibility gene. The Notch signalling system is one candidate system for controlling the switch and we have identified expression of Notch2 and Notch4 in seminomas and carcinoma in situ. Thus those two members of the Notch family are candidates for proto-oncogenes that could play a role in GCT development. We have also identified a human homologue of the synaptonemal complex protein, SCP3, and have found its apparently aberrant expression in some established EC cell lines. One possibility is that abnormal regulation of such proteins involved in the synaptonemal complex could also lead to genetic instability in PGC and so also initiate tumour development.     

Amniotic fluid stem cell-based models to study the effects of gene mutations and toxicants on male germ cell formation

Male infertility is a major public health issue predominantly caused by defects in germ cell development. In the past, studies on the genetic regulation of spermatogenesis as well as on negative environmental impacts have been hampered by the fact that human germ cell development is intractable to direct analysis in vivo. Compared with model organisms including mice, there are fundamental differences in the molecular processes of human germ cell development. Therefore, an in vitro model mimicking human sperm formation would be an extremely valuable research tool. In the recent past, both human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells have been reported to harbour the potential to differentiate into primordial germ cells and gametes. We here discuss the possibility to use human amniotic fluid stem (AFS) cells as a biological model. Since their discovery in 2003, AFS cells have been characterized to differentiate into cells of all three germ layers, to be genomically stable, to have a high proliferative potential and to be non-tumourigenic. In addition, AFS cells are not subject of ethical concerns. In contrast to iPS cells, AFSs cells do not need ectopic induction of pluripotency, which is often associated with only imperfectly cleared epigenetic memory of the source cells. Since AFS cells can be derived from amniocentesis with disease-causing mutations and can be transfected with high efficiency, they could be used in probing gene functions for spermatogenesis and in screening for male reproductive toxicity.     

人精原干细胞特异性标志的初步筛选

目的:寻求可能用于人精原干细胞(SSC)分离和纯化的特异性表面标志。方法:通过免疫组化方法,应用造血干细胞(HSC)表面标志c-kit、Thy-1,人胚胎干细胞(ES)表面标志阶段特异性胚胎抗原SSEA-3、SSEA-4、碱性磷酸酶(ALP),原始生殖细胞(PGC)标志SSEA-1以及小鼠SSC表面标志α6和β1整合素对成人及胎儿睾丸SSC的特异性表达进行筛选和鉴定。结果:在成人睾丸组织中,α6整合素在生精小管生殖细胞表面存在较广泛而显著阳性表达,而β1整合素主要在生精小管基底部细胞存在显著阳性染色,Thy-1在成人睾丸生精小管基底部细胞可见散在阳性染色,少量间质细胞中亦可见阳性染色。上述3种抗原标志在成人生殖细胞表面的表达具有一定的特异性。在胎儿睾丸生精小管中,可见SSEA-1在生殖细胞表面存在显著阳性表达,具有明显特异性。结论:α6、β1整合素和Thy-1可作为阳性标志用于人SSC的分选。SSEA-1可作为识别胎儿SSC的特异性标志。     

Why human extragonadal germ cell tumours occur in the midline of the body: old concepts, new perspectives

Hypotheses on the origin and distribution of extragonadal germ cell tumours (GCTs) and teratomas are briefly reviewed and revisited in the light of (i) new developments in the classification of GCTs, (ii) data on genomic imprinting of these neoplasms and (iii) the recent finding that germ cells can be derived from mouse and human embryonal stem (ES) cells. Only the Type I (infantile teratomas/yolk sac tumours) and Type II GCTs (seminomatous tumours and non-seminomas) occur in the gonads and extragonadal localizations. The data on genomic imprinting lend support to the hypothesis that they are derived from germ cells. These precursor cells could have differentiated from ES cells in extragonadal localizations. Their distribution along the midline of the body is still best explained by the migration of primitive germ cells during development. The narrower distribution of the Type II than the Type I GCTs is probably due to the more strict conditions for survival and proliferation of primordial germ cells (PGCs)/gonocytes from which the Type II tumours originate, when compared with the precursor cells of Type I tumours, probably primitive germ cells closer to the ES cell. The known niches in which the Type II tumours develop have in common that they contain feeder cells expressing stem cell factor (SCF) - the ligand for the SCF receptor c-KIT, involved in proliferation and survival of PGCs/gonocytes - and contain GBY including the gene TSPY.     

肿瘤干细胞的研究进展

肿瘤具有异质性的特征,随着研究的深入,越来越多的证据提示肿瘤组织中也存在少量具有干细胞性质的肿瘤干细胞,于是人们在此基础上提出了肿瘤干细胞学说,肿瘤干细胞已成为当今肿瘤研究领域的热点。目前,已经从白血病、脑肿瘤、乳腺癌、恶性黑色素瘤及前列腺癌等多种恶性肿瘤中初步分离鉴定出肿瘤干细胞。肿瘤干细胞学说的提出,使得靶向性杀伤肿瘤干细胞从而根治肿瘤成为可能。