Identification of genes expressed in human primordial germ cells at the time of entry of the female germ line into meiosis

Germ Cell Derivation from Pluripotent Stem Cells for Understanding In Vitro Gametogenesis

Assisted reproductive technologies (ARTs) have developed considerably in recent years; however, they cannot rectify germ cell aplasia, such as non-obstructive azoospermia (NOA) and oocyte maturation failure syndrome. In vitro gametogenesis is a promising technology to overcome infertility, particularly germ cell aplasia. Early germ cells, such as primordial germ cells, can be relatively easily derived from pluripotent stem cells (PSCs); however, further progression to post-meiotic germ cells usually requires a gonadal niche and signals from gonadal somatic cells. Here, we review the recent advances in in vitro male and female germ cell derivation from PSCs and discuss how this technique is used to understand the biological mechanism of gamete development and gain insight into its application in infertility.

Functional Testing of Primitive Oocyte-like Cells Developed in Ovarian Surface Epithelium Cell Culture from Small VSEL-like Stem Cells: Can They Be Fertilized One Day?

Data from the literature show that there are different populations of stem cells present in human adult ovaries, including small stem cells resembling very small embryonic-like stem cells (VSELs). These small ovarian stem cells with diameters of up to 5 μm are present in the ovarian surface epithelium and can grow into bigger, primitive oocyte-like cells that express several markers of a germinal lineage and exhibit pluripotency but not the zona pellucida structure when cultured in vitro. In this report, we present the results of the functional testing of such primitive oocyte-like cells from one patient with premature ovarian failure after insemination with her partners' sperm. Knowing that even immature oocytes collected in an in vitro fertilization program cannot be fertilized naturally, we were only interested in determining whether and how these cells react to added sperm and whether spermatozoa somehow "recognize" them. Interestingly, the primitive oocyte-like cells quickly released a zona pellucida-like structure in the presence of sperm. Two different populations of cells were distinguished, those with a thick and those with a thin zona pellucida-like structure. The primitive oocyte-like cells with a released zona pellucida-like structure expressed the pluripotency-related gene OCT4A (POU5F1) and zona pellucida-related gene ZP3, similar to oocytes obtained from in vitro fertilization but not somatic chondrocytes. In a small proportion of these cells, a single-spermatozoon was observed inside the cytoplasm, but no signs of fertilization were found. These observations may suggest a primitive "cortical reaction". Our data further confirm the presence of germinal stem cells in the ovarian surface epithelium cell culture.

Characterization of novel alternative splicing variants of Oct4 gene expressed in mouse pluripotent stem cells

Oct4 is an important transcription factor for maintaining self-renewal and pluripotency of pluripotent stem cells (PSCs). Human OCT4 can be alternatively spliced and generate OCT4a, OCT4b, and OCT4b1. In this study, we discovered the novel Oct4 variants of Oct4b' and Oct4b1-3 in mouse PSCs for the first time. The expression of Oct4b variants, especially for Oct4b', was down regulated along with the downregulation of Oct4a when stem cells were differentiated. We also found four Oct4 translational products that were differentially expressed in mouse PSCs under the different culture conditions. The constructs of Oct4b2 and Oct4b3 could be alternatively spliced into Oct4b and Oct4b' when constructs were transiently transfected in NIH3T3 cells. Oct4b' encoded a 189 aa protein, and Oct4b could generate three distinct proteins including Oct4b-246aa, Oct4b-221aa, and Oct4b-189aa. The Oct4b variants could be alternatively translated in different type cells under the control of internal ribosome entry site (IRES) element that is within 5' upstream sequence of Oct4b. These findings provide new insights into reconsidering Oct4 variants expression and its additional role in maintaining the pluripotency of stem cells.

New insights into human primordial germ cells and early embryonic development from single-cell analysis

Human preimplantation developmental studies are difficult to accomplish due to associated ethical and moral issues. Preimplantation cells are rare and exist only in transient cell states. From a single cell, it is very challenging to analyse the origination of the heterogeneity and complexity inherent to the human body. However, recent advances in single-cell technology and data analysis have provided new insights into the process of early human development and germ cell specification. In this Review, we examine the latest single-cell datasets of human preimplantation embryos and germ cell development, compare them to bulk cell analyses, and interpret their biological implications.

Transcriptomics analysis and human preimplantation development

The study of oocyte and preimplantation embryo biology has been regarded with great curiosity throughout scientific history, but it is not until the development of robust methods for in vitro observation and manipulation of animal gametes that developmental biology has flourished as a discipline. By far the biggest technical challenge in studying transcription in oocytes and early embryo has been the necessity of developing techniques that retain a high level of accuracy when starting from small amount of material. The objective of this narrative review is to summarize the knowledge gained about the embryonic preimplantation period in the human species from transcriptomics experiments, and to discuss technical limitations and solutions to the study of transcriptomics in these samples.

SIGNIFICANCE

In this review we identify key critical issues in performing transcriptomics experiments during the human preimplantation period, and identifying possible ways to overcome them. This, combined with a description of clinical perspectives and the definition of future avenues for research will provide useful for future research.

Insights into female germ cell biology: from in vivo development to in vitro derivations

Understanding the mechanisms of human germ cell biology is important for developing infertility treatments. However, little is known about the mechanisms that regulate human gametogenesis due to the difficulties in collecting samples, especially germ cells during fetal development. In contrast to the mitotic arrest of spermatogonia stem cells in the fetal testis, female germ cells proceed into meiosis and began folliculogenesis in fetal ovaries. Regulations of these developmental events, including the initiation of meiosis and the endowment of primordial follicles, remain an enigma. Studying the molecular mechanisms of female germ cell biology in the human ovary has been mostly limited to spatiotemporal characterizations of genes or proteins. Recent efforts in utilizing in vitro differentiation system of stem cells to derive germ cells have allowed researchers to begin studying molecular mechanisms during human germ cell development. Meanwhile, the possibility of isolating female germline stem cells in adult ovaries also excites researchers and generates many debates. This review will mainly focus on presenting and discussing recent in vivo and in vitro studies on female germ cell biology in human. The topics will highlight the progress made in understanding the three main stages of germ cell developments: namely, primordial germ cell formation, meiotic initiation, and folliculogenesis.

A Butter Aroma Recombinate Activates Human Class-I Odorant Receptors

With ∼400 olfactory G protein-coupled receptors (GPCR), humans sensitively perceive ∼230 key aroma compounds as best natural agonists of ∼10000 food volatiles. An understanding of odorant coding, thus, critically depends on the knowledge about interactions of key food aroma chemicals and their mixtures with their cognate receptors. Genetically designed test cell systems enable the screening, deorphaning, and characterization of single odorant receptors (OR). This study shows for the food aroma-specific and quantitative butter aroma recombinate, and its single components, specific in vitro class-I OR activity patterns, as well as the activation of selected OR in a concentration-dependent manner. Recently, chemosensory receptors, especially class-I OR, were demonstrated to be expressed on blood leukocytes, which may encounter foodborne aroma compounds postprandially. This study shows that butter aroma recombinate induced chemotaxis of isolated human neutrophils in a defined gradient, and in a concentration-dependent and pertussis toxin-sensitive manner, suggesting at least a GPCR-mediated activation of blood leukocytes by key food odorants.

Analysis of POU5F1, c-Kit, PLAP, AP2γ and SALL4 in gonocytes of patients with cryptorchidism

Cryptorchidism is a risk factor for the development of testicular germ cell tumors (TGCTs). The most common type of TGCT in cryptorchidism is seminoma. The intratubular germ cell neoplasia unclassified (ITGCNU) is a histological pattern preceding the development of seminomas and non-seminomas. It was suggested that in patients with cryptorchidism, the gonocytes remained undifferentiated with pluripotent abilities expressing proteins like POU domain class 5 transcription factor 1 (POU5F1), tyrosine kinase receptor c-Kit, placental-like alkaline phosphatase (PLAP), the transcription factor AP2γ and sal-like protein 4 (SALL4) that confer to the gonocytes this ability and therefore make them susceptible to develop ITGCNU. The aim of the present study was to determine if the gonocytes of patients with cryptorchidism express POU5F1, c-Kit, PLAP, AP2γ and SALL4 proteins after their differentiation period. Based on this, we evaluated samples of testicular tissue from newborns to 16-year old subjects with or without cryptorchidism in search of POU5F1, c-Kit, PLAP, AP2γ and SALL4 using immunocytochemical method, the results of which were validated by RT-PCR. The results showed that control subjects witnessed a down-regulation in the expression of these five proteins in the first year of life, which eventually disappeared. On the other hand, it was determined that 21.6% (8/37) of the patients with cryptorchidism continued to express, at least, one of the proteins analyzed in this study after the second year of life. And only 5.4% (2/37) of the patients were positive to the five markers. These data sustain the proposed hypothesis that in cryptorchid patients, ITGCNU arises from gonocytes that fail in their differentiation process to spermatogonia with conservation of the proteins (POU5F1, c-Kit, PLAP, AP2γ and SALL4) that maintain pluripotency and undifferentiated characteristics and which are responsible for making the gonocytes susceptible to malignancy. However, we cannot guarantee that these patients present neoplastic transformation.

Class I odorant receptors, TAS1R and TAS2R taste receptors, are markers for subpopulations of circulating leukocytes

Our cellular immune system has to cope constantly with foodborne substances that enter the bloodstream postprandially. Here, they may activate leukocytes via specific but yet mostly unknown receptors. Ectopic RNA expression out of gene families of chemosensory receptors, i.e., the ∼400 ORs, ∼25 TAS2R bitter-taste receptors, and the TAS1R umami- and sweet-taste receptor dimers by which we typically detect foodborne substances, has been reported in a variety of peripheral tissues unrelated to olfaction or taste. In the present study, we have now discovered, by gene-specific RT-PCR experiments, the mRNA expression of most of the Class I ORs (TAS1R) and TAS2R in 5 different types of blood leukocytes. Surprisingly, we did not detect Class II OR mRNA. By RT-qPCR, we show the mRNA expression of human chemosensory receptors and their cow orthologs in PMN, thus suggesting an evolutionary concept. By immunocytochemistry, we demonstrate that some olfactory and taste receptors are expressed, on average, in 40-60% of PMN and T or B cells and largely coexpress in the same subpopulation of PMN. The mRNA expression and the size of subpopulations expressing certain chemosensory receptors varied largely among individual blood samples, suggesting a regulated expression of olfactory and taste receptors in these cells. Moreover, we show mRNA expression of their downstream signaling molecules and demonstrate that PTX abolishes saccharin- or 2-PEA-induced PMN chemotactic migration, indicating a role for Gi-type proteins. In summary, our data suggest "chemosensory"-type subpopulations of circulating leukocytes.

Oct4 overexpression facilitates proliferation of porcine fibroblasts and development of cloned embryos

Octamer-binding transcription factor 4 (Oct4) is a critical molecule for the self-renewal and pluripotency of embryonic stem cells. Recent reports have shown that Oct4 also controls cell-cycle progression and enhances the proliferation of various types of cells. As the high proliferation of donor fibroblasts is critical to the production of transgenic pigs, using the somatic cell nuclear transfer technique, we analysed the effect of Oct4 overexpression on the proliferation of porcine fibroblasts and embryos. Porcine endogenous Oct4 cDNA was cloned, sequenced and inserted into an expression vector. The vector was transfected into porcine fibroblasts, and a stable Oct4-overexpressed cell line was established by antibiotic selection. Oct4 expression was validated by the immunostaining of Oct4. Cell morphology was changed to sharp, and both proliferation and migration abilities were enhanced in Oct4-overexpressed cells. Real-time RT-PCR results showed that p16, Bcl2 and Myc were upregulated in Oct4-overexpressed cells. Somatic cell nuclear transfer was performed using Oct4-overexpressed cells, and the development of Oct4 embryos was compared with that of wild-type cloned embryos. The cleavage and blastocyst formation rates were improved in the Oct4 embryos. Interestingly, blastocyst formation of the Oct4 embryos was observed as early as day 5 in culture, while blastocysts were observed from day 6 in wild-type cloned embryos. In conclusion, the overexpression of Oct4 enhanced the proliferation of both porcine fibroblasts and embryos.

The reprogramming factor nuclear receptor subfamily 5, group A, member 2 cannot replace octamer-binding transcription factor 4 function in the self-renewal of embryonic stem cells

Although octamer-binding transcription factor 4 (Oct-4) is one of the most intensively studied factors in mammalian development, no cellular genes capable of replacing Oct-4 function in embryonic stem (ES) cells have been found. Recent data show that nuclear receptor subfamily 5, group A, member 2 (Nr5a2) is able to replace Oct-4 function in the reprogramming process; however, it is unclear whether Nr5a2 can replace Oct-4 function in ES cells. In this study, the ability of Nr5a2 to maintain self-renewal and pluripotency in ES cells was investigated. Nr5a2 localized to the nucleus in ES cells, similarly to Oct-4. However, expression of Nr5a2 failed to rescue the stem cell phenotype or to maintain the self-renewal ability of ES cells. Furthermore, as compared with Oct-4-expressing ES cells, Nr5a2-expressing ES cells showed a reduced number of cells in S-phase, did not expand normally, and did not remain in an undifferentiated state. Ectopic expression of Nr5a2 in ES cells was not able to activate transcription of ES cell-specific genes, and gene expression profiling demonstrated differences between Nr5a2-expressing and Oct-4-expressing ES cells. In addition, Nr5a2-expressing ES cells were not able to form teratomas in nude mice. Taken together, these results strongly suggest that the gene regulation properties of Nr5a2 and Oct-4 and their abilities to confer self-renewal and pluripotency of ES cells differ. The present study provides strong evidence that Nr5a2 cannot replace Oct-4 function in ES cells.

Expression of stem cell markers: OCT4, KIT, ITGA6, and ITGB1 in the male germinal epithelium

Efforts have been made for the isolation and characterization of human stem spermatogonia (SG) which would be of major interest for fertility preservation in oncologic patients. We evaluated the expression of mammalian SG stem cell markers, KIT, OCT4, integrin alpha 6 (ITGA6), and integrin beta 1 (ITGB1) as possible indicators for the isolation of those cells in humans. Two different types of SG were individually isolated by micromanipulation from testicular biopsies of men with conserved spermatogenesis. Expression of mRNA showed the absence of KIT and ITGB1 markers in SG. By immunocytochemistry (IC), protein expression for KIT and integrins revealed two types of SG populations, negative (type-1) and positive (type-2). By immunohistochemistry (IH), protein expression for KIT and ITGB1 also revealed two kinds of SG populations, negative (SG A-dark) and positive (SG A-pale). Results suggest that in humans it may be possible to obtain pure populations of stem SG by using negative KIT((-))/ITGB1((-)) sorting.

Germ cell differentiation from pluripotent cells

Infertility is a medical condition with an increasing impact in Western societies with causes linked to toxins, genetics, and aging (primarily delay of motherhood). Within the different pathologies that can lead to infertility, poor quality or reduced quantity of gametes plays an important role. Gamete donation and therefore demand on donated sperm and eggs in fertility clinics is increasing. It is hoped that a better understanding of the conditions related to poor gamete quality may allow scientists to design rational treatments. However, to date, relatively little is known about human germ cell development in large part due to the inaccessibility of human development to molecular genetic analysis. It is hoped that pluripotent human embryonic stem cells and induced pluripotent stem cells may provide an accessible in vitro model to study germline development; these cells are able to differentiate to cells of all three primary embryonic germ layers, as well as to germ cells in vitro. We review the state of the art in germline differentiation from pluripotent stem cells.

An artificial sperm--next year or never?

The idea that a sperm or egg might be formed outside of a gonad is perhaps as bizarre today as human assisted conception and test-tube babies were 30-40 years ago and has received a similar amount of media copy. Here, we review briefly the derivation of mammalian germ cells and sperm cells from embryonic stem cells in vitro, ask whether these methods are viable and could provide therapies in the future, and discuss what constitutes an 'artificial' sperm.

Concise review: isoforms of OCT4 contribute to the confusing diversity in stem cell biology

The human OCT4 gene can generate at least three transcripts (OCT4A, OCT4B, and OCT4B1) and four protein isoforms (OCT4A, OCT4B-190, OCT4B-265, and OCT4B-164) by alternative splicing and alternative translation initiation. OCT4A is a transcription factor responsible for the pluripotency properties of embryonic stem (ES) cells. While OCT4B cannot sustain ES cell self-renewal, it may respond to cell stresses. Yet, the function of OCT4B1 is still unclear. Lack of distinction of OCT4 isoforms could lead to confusions and controversies on OCT4 in various tissues and cells. One important issue we emphasize in this review article is that alternatively spliced transcripts and alternative translation products of OCT4 exhibit diverse expression patterns and functions. Furthermore, simple approaches and methods to detect and distinguish OCT4 isoforms are discussed. This article underscores the importance of identifying and discriminating the expression and functions of OCT4 isoforms in stem cell research.

Identification and characterization of cancer stem cells in ovarian yolk sac tumors

Recent evidence supports the cancer stem cell theory, that is, that malignant tumors arise from cells termed cancer stem cells or tumor-initiating cells that have the ability to self-renew and are responsible for maintaining the tumor. Cells with marked tumor-initiating capacity have recently been identified in a number of solid tumors. CD133 (PROM1, human prominin-1) has been used as a marker to detect stem cells (progenitor cells) and cancer stem cells (tumor-initiating cells) in various tissues. Ovarian yolk sac tumors (YSTs) are rare and highly malignant. The present study was designed to evaluate the tumor-forming ability of CD133(+) cells in ovarian YST cell lines and to examine the characteristics of CD133(+) cells, such as cell growth and invasiveness. Our data suggest ovarian YST to be maintained by a rare fraction of cancer stem-like cells that express the cell surface marker CD133.

A data integration approach to mapping OCT4 gene regulatory networks operative in embryonic stem cells and embryonal carcinoma cells

It is essential to understand the network of transcription factors controlling self-renewal of human embryonic stem cells (ESCs) and human embryonal carcinoma cells (ECs) if we are to exploit these cells in regenerative medicine regimes. Correlating gene expression levels after RNAi-based ablation of OCT4 function with its downstream targets enables a better prediction of motif-specific driven expression modules pertinent for self-renewal and differentiation of embryonic stem cells and induced pluripotent stem cells.We initially identified putative direct downstream targets of OCT4 by employing CHIP-on-chip analysis. A comparison of three peak analysis programs revealed a refined list of OCT4 targets in the human EC cell line NCCIT, this list was then compared to previously published OCT4 CHIP-on-chip datasets derived from both ES and EC cells. We have verified an enriched POU-motif, discovered by a de novo approach, thus enabling us to define six distinct modules of OCT4 binding and regulation of its target genes.A selection of these targets has been validated, like NANOG, which harbours the evolutionarily conserved OCT4-SOX2 binding motif within its proximal promoter. Other validated targets, which do not harbour the classical HMG motif are USP44 and GADD45G, a key regulator of the cell cycle. Over-expression of GADD45G in NCCIT cells resulted in an enrichment and up-regulation of genes associated with the cell cycle (CDKN1B, CDKN1C, CDK6 and MAPK4) and developmental processes (BMP4, HAND1, EOMES, ID2, GATA4, GATA5, ISL1 and MSX1). A comparison of positively regulated OCT4 targets common to EC and ES cells identified genes such as NANOG, PHC1, USP44, SOX2, PHF17 and OCT4, thus further confirming their universal role in maintaining self-renewal in both cell types. Finally we have created a user-friendly database (http://biit.cs.ut.ee/escd/), integrating all OCT4 and stem cell related datasets in both human and mouse ES and EC cells.In the current era of systems biology driven research, we envisage that our integrated embryonic stem cell database will prove beneficial to the booming field of ES, iPS and cancer research.

Oct-4 controls cell-cycle progression of embryonic stem cells

Mouse and human ES (embryonic stem) cells display unusual proliferative properties and can produce pluripotent stem cells indefinitely. Both processes might be important for maintaining the 'stemness' of ES cells; however, little is known about how the cell-cycle fate is regulated in ES cells. Oct-4, a master switch of pluripotency, plays an important role in maintaining the pluripotent state of ES cells and may prevent the expression of genes activated during differentiation. Using ZHBTc4 ES cells, we have investigated the effect of Oct-4 on ES cell-cycle control, and we found that Oct-4 down-regulation in ES cells inhibits proliferation by blocking cell-cycle progression in G0/G1. Deletion analysis of the functional domains of Oct-4 indicates that the overall integrity of the Oct-4 functional domains is important for the stimulation of S-phase entry. We also show in the present study that the p21 gene is a target for Oct-4 repression. Furthermore, p21 protein levels were repressed by Oct-4 and were induced by the down-regulation of Oct-4 in ZHBTc4 ES cells. Therefore the down-regulation of p21 by Oct-4 may contribute to the maintenance of ES cell proliferation.

Y chromosome in Turner syndrome: review of the literature

Turner syndrome (TS) is one of the most common types of aneuploidy among humans, and is present in 1:2000 newborns with female phenotype. Cytogenetically, the syndrome is characterized by sex chromosome monosomy (45,X), which is present in 50-60% of the cases. The other cases present mosaicism, with a 45,X cell line accompanied by one or more other cell lines with a complete or structurally abnormal X or Y chromosome. The presence of Y-chromosome material in patients with dysgenetic gonads increases the risk of gonadal tumors, especially gonadoblastoma. The greatest concern is the high risk of developing gonadoblastoma or other tumors and virilization during puberty if chromosome Y-specific sequences are present. The role of the Y chromosome in human oncogenesis is still controversial. Even though gonadoblastoma is a benign tumor, it can undergo transformation into invasive dysgerminoma in 60% of the cases, and also into other, malignant forms of germ cell tumors. Although some authors have questioned the high incidence of gonadoblastoma (around 30%), the risk of developing any kind of gonadal lesion, whether tumoral or not, justifies investigation of Y-chromosome sequences by means of the polymerase chain reaction (PCR), a highly sensitive, low-cost and easy-to-perform technique. In conclusion, mosaicism of both the X and the Y chromosome is a common finding in TS, and detection of Y-chromosome-specific sequences in patients, regardless of their karyotype, is necessary in order to prevent the development of gonadal lesions.

Alternative translation of OCT4 by an internal ribosome entry site and its novel function in stress response

OCT4 is a pivotal transcription factor in maintaining the pluripotency and self-renewal capacities of embryonic stem (ES) cells. Human OCT4 can generate two isoforms by alternative splicing, termed OCT4A and OCT4B. OCT4A confers the stemness properties of ES cells, whereas the function of OCT4B is unknown. We present here the diverse protein products and a novel function of OCT4 gene. A single OCT4B mRNA can encode three isoforms by alternative translation initiation at AUG and CUG start codons, respectively. A putative internal ribosome entry site (IRES) has been identified in OCT4B mRNA accounting for the translation mechanism. The OCT4B-190 is upregulated under stress conditions and it may protect cell against apoptosis under stress. This work evokes the significance to distinguish the biological function of the protein products of OCT4. The OCT4 gene, by the regulation of alternative splicing and alternative translation initiation, may carry out more crucial roles in many biological events.

Mesenchymal to embryonic incomplete transition of human cells by chimeric OCT4/3 (POU5F1) with physiological co-activator EWS

POU5F1 (more commonly known as OCT4/3) is one of the stem cell markers, and affects direction of differentiation in embryonic stem cells. To investigate whether cells of mesenchymal origin acquire embryonic phenotypes, we generated human cells of mesodermal origin with overexpression of the chimeric OCT4/3 gene with physiological co-activator EWS (product of the EWSR1 gene), which is driven by the potent EWS promoter by translocation. The cells expressed embryonic stem cell genes such as NANOG, lost mesenchymal phenotypes, and exhibited embryonal stem cell-like alveolar structures when implanted into the subcutaneous tissue of immunodeficient mice. Hierarchical analysis by microchip analysis and cell surface analysis revealed that the cells are subcategorized into the group of human embryonic stem cells and embryonal carcinoma cells. These results imply that cells of mesenchymal origin can be traced back to cells of embryonic phenotype by the OCT4/3 gene in collaboration with the potent cis-regulatory element and the fused co-activator. The cells generated in this study with overexpression of chimeric OCT4/3 provide us with insight into cell plasticity involving OCT4/3 that is essential for embryonic cell maintenance, and the complexity required for changing cellular identity.

Comparative immunohistochemical characterization of canine seminomas and Sertoli cell tumors

Primary testicular tumors are the most common causes of cancer in male dogs. Overall, the majority of canine patients should be cured by testicular surgery. However, tumor markers are not well-known in veterinary medicine. We sought to determine using immunohistochemistry whether the combined human testicular tumor markers (placental alkaline phosphatase, OCT3/4, CD30, alpha-fetoprotein, inhibin-alpha, vimentin, c-KIT, and desmin) are expressed in canine seminomas and Sertoli cell tumors (SCTs). We examined 35 canine testicular tumors, 20 seminomas and 15 SCTs. c-KIT was expressed markedly in canine seminomas. Both inhibin-alpha and vimentin were expressed significantly in canine SCTs. The results of this study demonstrate differences and similarities between tumor marker expression of testicular tumors in dogs and humans. All the main markers in current routine use are discussed as well as potential useful markers for benign and malignant tumors, and tumor progression.

Mutation in the DNA-binding domain of the EWS-Oct-4 oncogene results in dominant negative activity that interferes with EWS-Oct-4-mediated transactivation

The EWS-Oct-4 protein is a chimeric molecule in which the amino terminal domain (NTD) of the EWS becomes fused to the carboxy terminal domain (CTD) of the Oct-4 transcription factor. It was identified in human bone and soft-tissue tumors associated with t(6;22)(p21;q12). Using in vitro and in vivo systems, we found that the EWS-Oct-4 protein self-associates. The major domains required for self-association mapped to the EWS NTD (amino acids 70-163) and the POU DNA-binding domain. EWS-Oct-4 protein also associated with EWS-Oct-4 (V351P), which contains a mutation in the POU DNA-binding domain. Using electrophoretic mobility shift assays, we found that the EWS-Oct-4 (V351P) mutant interfered with wild-type EWS-Oct-4 DNA-binding activity. In addition, we found that EWS-Oct-4-mediated transcriptional activation was inhibited by EWS-Oct-4 (V351P) protein in vivo. Thus, this mutation in the POU DNA-binding domain results in a dominant negative protein. These findings suggest that the biological functions of the EWS-Oct-4 oncogene can be modulated by the dominant negative mutant EWS-Oct-4 (V351P).

Recent advances in the derivation of germ cells from the embryonic stem cells

In recent years, considerable progress has been made in the establishment and differentiation of human embryonic stem (ES) cell lines. The primordial germ cells (PGCs) and embryonic germ (EG) cells derived from them share many of their properties with ES cells. ES cell lines have now been derived from different stages of germ cell development and they have differentiated into gametes and shown embryonic development in mice, including the production of live pups. Conversely, germ cells can also be derived from ES cells. It has been demonstrated that murine (m) ES cells can differentiate into PGCs and subsequently into early gametes (oocytes and sperms) and blastocysts. Recently, immature sperm cells derived from mES cells in culture have produced live offspring. Preliminary research has indicated that human (h) ES cells probably have the potential to differentiate into germ cells. Adult stem cells have been reported to differentiate into mature germ cells in vitro. Therefore, stem cells may offer a valuable in vitro model for the investigation of germ cell development and the early stages of human gametogenesis, including epigenetic modifications of the germ line. This review discusses recent developments in the derivation and specification of mammalian germ cells from ES cells and describes some of the mechanisms of germ cell development.

Cancer stem cells as targets for cancer therapy: selected cancers as examples

It is becoming increasingly evident that cancer constitutes a group of diseases involving altered stem-cell maturation/differentiation and the disturbance of regenerative processes. The observed malignant transformation is merely a symptom of normal differentiation processes gone astray rather than the primary event. This review focuses on the role of cancer stem cells (CSCs) in three common but also relatively under-investigated cancers: head and neck, ovarian, and testicular cancer. For didactic purpose, the physiology of stem cells is first introduced using hematopoietic and mesenchymal stem cells as examples. This is followed by a discussion of the (possible) role of CSCs in head and neck, ovarian, and testicular cancer. Aside from basic information about the pathophysiology of these cancers, current research results focused on the discovery of molecular markers specific to these cancers are also discussed. The last part of the review is largely dedicated to signaling pathways active within various normal and CSC types (e.g. Nanog, Nestin, Notch1, Notch2, Oct3 and 4, Wnt). Different elements of these pathways are also discussed in the context of therapeutic opportunities for the development of targeted therapies aimed at CSCs. Finally, alternative targeted anticancer therapies arising from recently identified molecules with cancer-(semi-)selective capabilities (e.g. apoptin, Brevinin-2R) are considered.

Pyruvate kinase isozyme type M2 (PKM2) interacts and cooperates with Oct-4 in regulating transcription

The Oct-4 gene encodes a transcription factor that plays an important role in maintaining the pluripotent state of embryonic stem cells and may prevent expression of genes activated during differentiation. Although its role in maintaining embryonic stem cell pluripotency is well established, there is still little known about the binding partners that regulate its function. To identify proteins that control Oct-4 function, we used affinity chromatography on immobilized Oct-4 (POU) together with MALDI-TOF (matrix-assisted laser-desorption ionization-time-of-flight) MS (mass spectrometry) and isolated a novel Oct-4-interacting protein, pyruvate kinase type M2 (PKM2 or M2-PK). PKM2 is an isozyme of pyruvate kinase that is specifically expressed in proliferating cells, such as embryonic stem cells, embryonic carcinoma cells, as well as cancer cells. Oct-4 and PKM2 were co-affinity precipitated from cell extracts, and glutathione S-transferase pull-down assays revealed that the POU DNA binding domain of Oct-4 was required for interaction with PKM2. In addition, the C-terminal domain of PKM2 (amino acids 307-531) was involved in binding to Oct-4. Moreover, ectopic expression of the PKM2 enhanced Oct-4-mediated transcription. These observations indicate that the transactivation potential of the Oct-4 transcription factor is positively modulated by PKM2.

The EWS-Oct-4 fusion gene encodes a transforming gene

The t(6;22)(p21;q12) translocation associated with human bone and soft-tissue tumours results in a chimaeric molecule fusing the NTD (N-terminal domain) of the EWS (Ewing's sarcoma) gene to the CTD (C-terminal domain) of the Oct-4 (octamer-4) embryonic gene. Since the N-terminal domains of EWS and Oct-4 are structurally different, in the present study we have assessed the functional consequences of the EWS-Oct-4 fusion. We find that this chimaeric gene encodes a nuclear protein which binds DNA with the same sequence specificity as the parental Oct-4 protein. Comparison of the transactivation properties of EWS-Oct-4 and Oct-4 indicates that the former has higher transactivation activity for a known target reporter gene containing Oct-4 binding. Deletion analysis of the functional domains of EWS-Oct-4 indicates that the EWS (NTD), the POU domain and the CTD of EWS-Oct-4 are necessary for full transactivation potential. EWS-Oct-4 induced the expression of fgf-4 (fibroblast growth factor 4) and nanog, which are potent mitogens as well as Oct-4 downstream target genes whose promoters contain potential Oct-4-binding sites. Finally, ectopic expression of EWS-Oct-4 in Oct-4-null ZHBTc4 ES (embryonic stem) cells resulted in increased tumorigenic growth potential in nude mice. These results suggest that the oncogenic effect of the t(6;22) translocation is due to the EWS-Oct-4 chimaeric protein and that fusion of the EWS NTD to the Oct-4 DNA-binding domain produces a transforming chimaeric product.

Aberrant expression and distribution of the OCT-4 transcription factor in seminomas

Testicular germ cell tumors (TGCTs), comprised of seminomas and non-seminomas, are derived from premalignant and noninvasive intracellular germ cell neoplasias. Among TGCTs, seminomas are believed to resemble a transformed state of primordial germ cells (PGCs) and are known to exhibit a gene expression profile similar to that of embryonic stem (ES) cells, such as transcription factor OCT-4. OCT-4 has recently been recognized as a diagnostic marker for clinical aspects of seminomas. However, the role of the OCT-4 protein in seminomas has not been clarified. To determine a possible role of the OCT-4 protein in seminomas, in this paper, we studied a series of 41 testicular tumor tissues and four cell lines by immunohistochemistry, Western blotting, and reverse-transcriptase polymerase chain reaction (RT-PCR) to examine the expression and distribution of the OCT-4 transcription factor in seminomas. By utilizing immunohistochemical staining and Western blotting, we demonstrated that the OCT-4 transcription factor was aberrantly localized in the cytoplasm and nuclei of cells in the collected seminoma tissues. This observation was further confirmed using immunocytochemical staining of NCCIT (seminoma-embryonal carcinoma) and NT2 (embryonal carcinoma) cells. In addition, the RT-PCR results indicated that Oct-4 mRNA was relatively highly expressed in NCCIT, NT2 cells, and seminoma tissues when compared with human embryonic stem cells. The aberrant expression and distribution of the OCT-4 transcription factor in seminomas may provide some important clues concerning the cell transformation between germ line stem cells (like PGC) and testicular germ cell tumors.

Fibroblast-like cells derived from the gonadal ridges and dorsal mesenteries of human embryos as feeder cells for the culture of human embryonic germ cells

The establishment of optimal hEG culture systems is a major challenge for the field of embryonic germ cell research. It is important to find appropriate feeder cells to support the growth of hEG. The clinical application of human embryonic germ cells cultured on mouse-derived feeder cells is restricted, since human embryonic germ cells cultured on mouse-derived feeder cells are at risk of contamination by heterogeneous proteins or pathogens. In order to avoid this limitation, we have isolated and cultured three human embryonic fibroblast-like cell lines derived from the gonadal ridges and dorsal mesenteries of 5- to 10-week old embryos. These cells expressed basic fibroblast growth factor and leukemia inhibitory factor, both essential for the growth of human embryonic germ cells. We then used the mitomycin-inactivited human embryonic fibroblast-like cells as feeder cells to culture human embryonic germ cells derived from the gonadal ridges and dorsal mesenteries of 5- to 10-week old embryos. Of 21 human primordial germ cell cultures initiated, seven were continuously grown and split for 10 passages with normal and stable human karyotypes. These cells expressed markers characteristic of pluripotent stem cells, including alkaline phosphatase, stage-specific embryonic antigens (SSEA)-1, SSEA-3, SSEA-4, tumor related antigens (TRA)-1-60, TRA-1-81, and the POU transcription factor Octamer-4 (Oct-4). Moreover, the cells possessed the capacity to differentiate into all three primary germ layers (ectoderm, mesoderm, and endoderm). Therefore, we have successfully used the human embryonic fibroblast-like cells derived from gonadal ridges and dorsal mesenteries as feeder cells to culture proliferative, undifferentiated and pluripotent human embryonic germ cells.

Generation of amplified RNAs and cDNA libraries from single mammalian cells

With the near completion of the human genome sequencing effort, it is now possible to analyze the expression of the entire human gene complement. However, a major obstacle in performing such analysis is the ability to successfully generate enough cDNA or amplified RNA from a limited number of cells, such as biopsies, blood smears, cells obtained by laser capture microscopy, and preimplantation embryonic cells and germ cells. Because these samples yield extremely small amounts of RNA, reproducible methods are needed to amplify this RNA while maintaining the original message profile. A detailed description is given for generating pools of cDNA libraries containing a high proportion of cDNAs enriched with 5'-coding sequences from as little as 1 ng of total RNA using a modified switching mechanism at 5' end of RNA transcript protocol. In addition, the T7-promoter-linked double-stranded cDNAs can be in vitro transcribed linearly using T7-RNA polymerase to generate amplified RNA that is mRNA derived. The cDNA pools can be used directly for gene-specific reverse transcriptase polymerase chain reaction or processed for ligation into vectors of choice whereas the amplified RNA can be used for microarray-based expression profiling.

Global gene expression analysis in fetal mouse ovaries with and without meiosis and comparison of selected genes with meiosis in the testis

In order to identify novel genes involved in early meiosis and early ovarian development in the mouse, we used microarray technology to compare transcriptional activity in ovaries without meiotic germ cells at embryonic age 11.5 (E11.5) and E13.5 ovaries with meiosis. Overall, 182 genes were differentially expressed; 134 were known genes and 48 were functionally uncharacterized. A comparison of our data with the literature associated, for the first time, at least eight of the known genes with female meiosis/germ cell differentiation (Aldh1a1, C2pa, Tex12, Stk31, Lig3, Id4, Recql, Piwil2). These genes had previously only been described in spermatogenesis. The microarray also detected an abundance of vesicle-related genes of which four were upregulated (Syngr2, Stxbp1, Ric-8, SytIX) and one (Myo1c) was downregulated in E13.5 ovaries. Detailed analysis showed that the temporal expression of SytIX also coincided with the first meiotic wave in the pubertal testis. This is the first time that SytIX has been reported in non-neuronal tissue. Finally, we examined the expression of one of the uncharacterized genes and found it to be gonad-specific in adulthood. We named this novel transcript "Gonad-expressed transcript 1" (Get-1). In situ hybridization showed that Get-1 was expressed in meiotic germ cells in both fetal ovaries and mature testis. Get-1 is therefore a novel gene in both male and female meiosis.

Analysis of Oct4-dependent transcriptional networks regulating self-renewal and pluripotency in human embryonic stem cells

The POU domain transcription factor OCT4 is a key regulator of pluripotency in the early mammalian embryo and is highly expressed in the inner cell mass of the blastocyst. Consistent with its essential role in maintaining pluripotency, Oct4 expression is rapidly downregulated during formation of the trophoblast lineage. To enhance our understanding of the molecular basis of this differentiation event in humans, we used a functional genomics approach involving RNA interference-mediated suppression of OCT4 function in a human ESC line and analysis of the resulting transcriptional profiles to identify OCT4-dependent genes in human cells. We detected altered expression of >1,000 genes, including targets regulated directly by OCT4 either positively (NANOG, SOX2, REX1, LEFTB, LEFTA/EBAF DPPA4, THY1, and TDGF1) or negatively (CDX2, EOMES, BMP4, TBX18, Brachyury [T], DKK1, HLX1, GATA6, ID2, and DLX5), as well as targets for the OCT4-associated stem cell regulators SOX2 and NANOG. Our data set includes regulators of ACTIVIN, BMP, fibroblast growth factor, and WNT signaling. These pathways are implicated in regulating human ESC differentiation and therefore further validate the results of our analysis. In addition, we identified a number of differentially expressed genes that are involved in epigenetics, chromatin remodeling, apoptosis, and metabolism that may point to underlying molecular mechanisms that regulate pluripotency and trophoblast differentiation in humans. Significant concordance between this data set and previous comparisons between inner cell mass and trophectoderm in human embryos indicates that the study of human ESC differentiation in vitro represents a useful model of early embryonic differentiation in humans.

The transcriptome of human oocytes

The identification of genes and deduced pathways from the mature human oocyte can help us better understand oogenesis, folliculogenesis, fertilization, and embryonic development. Human metaphase II oocytes were used within minutes after removal from the ovary, and its transcriptome was compared with a reference sample consisting of a mixture of total RNA from 10 different normal human tissues not including the ovary. RNA amplification was performed by using a unique protocol. Affymetrix Human Genome U133 Plus 2.0 GeneChip arrays were used for hybridizations. Compared with reference samples, there were 5,331 transcripts significantly up-regulated and 7,074 transcripts significantly down-regulated in the oocyte. Of the oocyte up-regulated probe sets, 1,430 have unknown function. A core group of 66 transcripts was identified by intersecting significantly up-regulated genes of the human oocyte with those from the mouse oocyte and from human and mouse embryonic stem cells. GeneChip array results were validated using RT-PCR in a selected set of oocyte-specific genes. Within the up-regulated probe sets, the top overrepresented categories were related to RNA and protein metabolism, followed by DNA metabolism and chromatin modification. This report provides a comprehensive expression baseline of genes expressed in in vivo matured human oocytes. Further understanding of the biological role of these genes may expand our knowledge on meiotic cell cycle, fertilization, chromatin remodeling, lineage commitment, pluripotency, tissue regeneration, and morphogenesis.

The human OCT-4 isoforms differ in their ability to confer self-renewal

OCT-4 transcription factors play an important role in maintaining the pluripotent state of embryonic stem cells and may prevent expression of genes activated during differentiation. Human OCT-4 isoform mRNAs encode proteins that have identical POU DNA binding domains and C-terminal domains but differ in their N-terminal domains. We report here the cloning and characterization of the human OCT-4B isoform. Human OCT-4B cDNA encodes a 265-amino acid protein with a predicted molecular mass of 30 kDa. Embryonic stem (ES) cell-based complementation assays using ZHBTc4 ES cells showed that unlike human OCT-4A, OCT-4B cannot sustain ES cell self-renewal. In addition, OCT-4B does not bind to a probe carrying the OCT-4 consensus binding sequence, and we demonstrate that two separate regions of its N-terminal domain are responsible for inhibiting DNA binding. We also demonstrate that OCT-4B is mainly localized to the cytoplasm. Overexpression of OCT-4B did not activate transcription from OCT-4-dependent promoters, although OCT-4A did as reported previously. Furthermore, transcriptional activation by human OCT-4A was not inhibited by co-expression of OCT-4B. Taken together, these data suggest that the DNA binding, transactivation, and abilities to confer self-renewal of the human OCT-4 isoforms differ.

Changing genetic world of IVF, stem cells and PGD. B. Polarities and gene expression in differentiating embryo cells and stem cells

Novel genetic techniques in the later twentieth century led to new analytical methods for assessing the growth of embryos and stem cells and improve preimplantation diagnosis. Increasing attention to the nature of polarities in mouse and human embryos revealed the existence of an animal-vegetal axis in human oocytes and embryos. Combinations of meridional and transverse cleavage divisions, the latter due to spindle rotation, determined the unequal division of ooplasm to embryonic blastomeres. Blastomeres with differing functions were accordingly formed in 4-cell embryos, including founders of inner cell mass and trophectoderm. New forms of gene analysis led to the polymerase chain reaction, while fluorescence in-situ hybridization revealed astonishingly high degrees of heteroploidy in human embryos. Developmental genetics gained immense analytical power as cDNA libraries, microarrays, transcriptomes RNAi and other methods clarified the roles of hundreds of genes in pre- and early post-implantation embryos and stem cells.

Pluripotent Stem Cells from Germ Cells

To date, stem cells have been derived from three sources of germ cells. These include embryonic germ cells (EGCs), embryonal carcinoma cells (ECCs), and multipotent germ line stem cells (GSCs). EGCs are derived from primordial germ cells that arise in the late embryonic and early fetal period of development. ECCs are derived from adult testicular tumors whereas GSCs have been derived by culturing spermatogonial stem cells from mouse neonates and adults. For each of these lines, their pluripotency has been demonstrated by their ability to differentiate into cell types derived from the three germ layers in vitro and in vivo and in chimeric animals, including germ line transmission. These germ line-derived stem cells have been generated from many species including human, mice, porcine, and chicken albeit with only slight modifications. This chapter describes general considerations regarding critical aspects of their derivation compared with their counterpart, embryonic stem cells (ESCs). Detailed protocols for EGC derivation and maintenance from human and mouse primordial germ cells (PGCs) will be presented.

Initial differentiation of blastomeres in 4-cell human embryos and its significance for early embryogenesis and implantation

This brief review is devoted to the nature of early blastomere differentiation in human 4-cell embryos and its consequences for embryonic development. Precursor cells of inner cell mass, germline, and trophectoderm may be formed at this stage, the clearest evidence being available for trophectoderm. The sites of these precursor cells in the embryo could be ascertained using markers for animal and vegetal poles, observing specific cleavage planes, and assessing gene and protein expression. This opens new opportunities for studying 4-cell embryos and removing or replacing specific cells. Knowledge of the properties of individual blastomeres should help in improving assisted human reproduction, performing preimplantation genetic diagnosis, and perhaps establishing specific stem cell lines. Special attention is paid to well-characterized trophectoderm, the trophectoderm stem cell, and possible new forms of clinical application.

Mouse ovary developmental RNA and protein markers from gene expression profiling

To identify genes involved in morphogenetic events during mouse ovary development, we started with microarray analyses of whole organ RNA. Transcripts for 60% of the 15,000 gene NIA panel were detected, and about 2000 were differentially expressed in nascent newborn compared to adult ovary. Highly differentially expressed transcripts included noncoding RNAs and newly detected genes involved in transcription regulation and signal transduction. The phased pattern of newborn mouse ovary differentiation allowed us to (1) extend information on activity and stage specificity of cell type-specific genes; and (2) generate a list of candidate genes involved in primordial follicle formation, including podocalyxin (Podxl), PDGFR-beta, and a follistatin-domain-encoding gene Flst1. Oocyte-specific transcripts included many (e.g., Deltex2, Bicd2, and Zfp37) enriched in growing oocytes, as well as a novel family of untranslated RNA's (RLTR10) that is selectively expressed in early stage follicles. The results indicate that global expression profiling of whole organ RNA provides sensitive first-line information about ovarian histogenesis for which no in vitro cell models are currently available.

Stimulation of Oct-4 Activity by Ewing's Sarcoma Protein

The Oct-4 gene encodes a transcription factor that is expressed in embryonic stem (ES) cells and germ cells. Oct-4 is known to function as a transcriptional activator of genes involved in maintaining an undifferentiated totipotent state and possibly in preventing expression of genes activated during differentiation. In addition, it is a putative proto-oncogene and a critical player in the genesis of human testicular germ cell tumors. Although much effort has gone toward characterizing Oct-4, there is still little known about the molecular mechanisms and the proteins that regulate Oct-4 function. To identify cofactors that control Oct-4 function in vivo, we used a recently developed bacterial two-hybrid screening system and isolated a novel ES cell-derived cDNA encoding Ewing's sarcoma protein (EWS). EWS is a proto-oncogene and putative RNA-binding protein involved in human cancers. By using glutathione-S-transferase (GST) pull-down assays, we were able to confirm the interaction between Oct-4 and EWS in vitro, and moreover, coimmunoprecipitation and colocalization studies have shown that these proteins also associate in vivo. We have mapped the EWS-interacting region to the POU domain of Oct-4. In addition, three independent sites on EWS are involved in binding to Oct-4. In this study, we report that Oct-4 and EWS are coexpressed in the pluripotent mouse and human ES cells. Consistent with its ability to bind to and colocalize with Oct-4, ectopic expression of EWS enhances the transactivation ability of Oct-4. Moreover, a chimeric protein generated by fusion of EWS (1-295) to the GAL4 DNA-binding domain significantly increases promoter activity of a reporter containing GAL4 DNA-binding sites, suggesting the presence of a strong activation domain within EWS. Taken together, our results suggest that Oct-4-mediated transactivation is stimulated by EWS.

Epigenetics and the germline

Epigenetic processes affect three stages of germline development, namely (1) specification and formation of primordial germ cells and their germline derivatives through lineage-specific epigenetic modifications, in the same manner as other embryonic lineages are formed, (2) a largely genome-wide erasure and re-establishment of germline-specific epigenetic modifications that only occurs in the embryonic primordial germ cell lineage, followed by re-establishment of sex-specific patterns during gametogenesis, and (3) differential epigenetic modifications to the mature male and female gamete genomes shortly after fertilisation. This review will detail current knowledge of these three processes both at the genome-wide level and at specific imprinted loci. The consequences of epigenetic perturbation are discussed and new in vitro models which may allow further understanding of a difficult developmental period to study, especially in the human, are highlighted.

Transcripts from a human primordial follicle cDNA library

BACKGROUND

Human primordial follicles (PFs) or the oocyte-pre-granulosa complex, constitute the earliest and most immature stage of human oogenesis. The factors, signalling networks and the precise role of the oocyte and the pre-granulosa cells in initiating growth and recruitment from this finite resting pool remain largely unknown at present.

METHODS

To obtain a gene resource of this oogenesis stage and thereby determine a molecular blueprint of the human PF, a cDNA library was constructed from 50 isolated human PFs using the phagemid vector pTriplEx2.

RESULTS

Sequence analysis showed that 46.67% of these clones corresponded to known genes while 29.48% were uncharacterized genes that included hypothetical proteins, human cDNA clones and novel genes. Bioinformatics analysis revealed a preponderance of mitochondrial genes and repeat elements followed by ribosomal proteins, transcription and translation genes. Transcripts for heat shock proteins, cell cycle, embryogenesis genes and apoptosis genes were identified. Members of the ubiquitin-proteasome pathway, MAPK, p38/JNK, GPCR, Wnt, NF-kappaB and notch signalling pathways were identified. A mitochondrial pathway and a transcription factor pathway in the human PF were generated. The gene networks in the transcription factor pathway provided a first glimpse of the balance between proliferation and cell death/apoptosis in this earliest stage of oogenesis.

CONCLUSIONS

The abundance and diversity of retroviral elements and transcriptional repressor genes in the human PF suggest these could contribute to the maintainance of this oogenesis stage. The role of these genes in initial recruitment and in subsequent oogenesis stages will be greatly facilitated and elucidated by printing a human PF cDNA array of the sequenced clones and using it for gene profiling.

Differentiation and development of human female germ cells during prenatal gonadogenesis: an immunohistochemical study

BACKGROUND

In the development of the human ovary, the second trimester includes the transition from oogonial replication to primordial follicle formation. The present study was carried out to assess differentiation and proliferation of germ cells in a series of female gonads from 19 fetuses from the second and third trimester, and two neonates.

METHODS

Using immunohistochemistry, the following markers were studied: placental/germ-like cell alkaline phosphatases (PLAP), the marker of pluripotency OCT3/4, the proliferation marker Ki-67, beta-catenin and E-cadherin, the stem cell factor receptor c-KIT, and VASA, a protein specific for the germ cell lineage.

RESULTS

PLAP and OCT3/4 were seen during oogenesis, but not in germ cells engaged in folliculogenesis. A similar pattern was observed for Ki-67. Loss of pluripotency occurs once oocytes engage in follicle formation, suggesting a role of cell-cell interactions in the process of germ cell maturation. VASA, c-KIT, beta-catenin and E-cadherin were found in germ cells at all developmental stages of oogenesis and folliculogenesis.

CONCLUSIONS

Immunohistochemically, two groups of germ cells can be distinguished. Germ cells that are predominantly found in the cortical region of the ovary before weeks 22-24 of gestation, showing an immature phenotype, are mitotically active, and express OCT3/4, a marker of pluripotency. On the other hand, germ cells undergoing folliculogenesis have lost their pluripotent potential and no longer proliferate.

Whole-genome approaches for large-scale gene identification and expression analysis in mammalian preimplantation embryos

The elucidation, unravelling and understanding of the molecular basis of transcriptional control during preimplantion development is of utmost importance if we are to intervene and eliminate or reduce abnormalities associated with growth, disease and infertility by applying assisted reproduction. Importantly, these studies should enhance our knowledge of basic reproductive biology and its application to regenerative medicine and livestock production. A major obstacle impeding progress in these areas is the ability to successfully generate molecular portraits of preimplantation embryos from their minute amounts of RNA. The present review describes the various approaches whereby classical embryology fuses with molecular biology, high-throughput genomics and systems biology to address and solve questions related to early development in mammals.

Diagnostic value of OCT3/4 for pre-invasive and invasive testicular germ cell tumours

Human testicular germ cell tumours of adolescents and adults (TGCTs), the seminomatous and non-seminomatous germ cell tumours, show morphological and biological similarities to normal embryonic development, presumably determined by their supposed cell of origin, the primordial germ cell/gonocyte. Based on this knowledge, OCT3/4, also known as POU5F1, was recently defined as a diagnostic marker for these tumour types. In the adult testis, positive immunohistochemistry for OCT3/4 is an absolute indicator for the presence of the TGCT precursor carcinoma in situ/intratubular germ cell neoplasia undifferentiated (CIS/ITGCNU), seminoma, and/or embryonal carcinoma. Several studies have confirmed this observation, using the same polyclonal antibody. The present study demonstrates the usefulness of OCT3/4 immunohistochemistry in a diagnostic setting of a consecutively collected series of more than 200 testicular tumours and over 80 testicular biopsies. Moreover, it is shown that a monoclonal antibody directed against OCT3/4 is as informative as the polyclonal antibody, both in immunohistochemistry and in western blot analysis. The antibodies are robust and applicable with different methods of pretreatment and storage of tissue. This allows routine application of this diagnostic marker.

Cross-species hybridisation of human and bovine orthologous genes on high density cDNA microarrays

BACKGROUND

Cross-species gene-expression comparison is a powerful tool for the discovery of evolutionarily conserved mechanisms and pathways of expression control. The usefulness of cDNA microarrays in this context is that broad areas of homology are compared and hybridization probes are sufficiently large that small inter-species differences in nucleotide sequence would not affect the analytical results. This comparative genomics approach would allow a common set of genes within a specific developmental, metabolic, or disease-related gene pathway to be evaluated in experimental models of human diseases. The objective of this study was to investigate the feasibility and reproducibility of cross-species analysis employing a human cDNA microarray as probe.

RESULTS

As a proof of principle, total RNA derived from human and bovine fetal brains was used as a source of labelled targets for hybridisation onto a human cDNA microarray composed of 349 characterised genes. Each gene was spotted 20 times representing 6,980 data points thus enabling highly reproducible spot quantification. Employing high stringency hybridisation and washing conditions, followed by data analysis, revealed slight differences in the expression levels and reproducibility of the signals between the two species. We also assigned each of the genes into three expression level categories- i.e. high, medium and low. The correlation co-efficient of cross hybridisation between the orthologous genes was 0.94. Verification of the array data by semi-quantitative RT-PCR using common primer sequences enabled co-amplification of both human and bovine transcripts. Finally, we were able to assign gene names to previously uncharacterised bovine ESTs.

CONCLUSIONS

Results of our study demonstrate the harnessing and utilisation power of comparative genomics and prove the feasibility of using human microarrays to facilitate the identification of co-expressed orthologous genes in common tissues derived from different species.