Genes associated with the formation of germ cells from embryonic stem cells in cultures containing different glucose concentrations

Germ cell differentiation of mouse embryonic stem cells can be influenced by the culture medium

Although embryonic stem (ES) cells can differentiate into germ cells, little is known about the influence of culture media on this process. We investigated the effect of two culture media on the capacity of ES cells to differentiate into germ cells using embryoid body (EB) and monolayer culture protocols. Germ cell differentiation was induced in mouse ES cells under four experimental conditions: EB/Dulbecco's modified Eagle's medium (EB/DMEM), EB/knockout Dulbecco's modified Eagle's medium (EB/KO-DMEM), monolayer/Dulbecco's modified Eagle's medium (monolayer/DMEM), and monolayer/knockout Dulbecco's modified Eagle's medium (monolayer/KO-DMEM). After incubation for 6 days, quantitative real-time polymerase chain reaction (qRT-PCR) was used to assess expression of the germ cell markers, Mvh, Oct4, Rec8, Scp1, Scp3 and Stra8. Also, Oct4 and Mvh expressions at the protein level were assessed using immunocytochemistry; we evaluated alkaline phosphatase activity in addition to cell number and viability. Germ cell-specific marker expression was increased significantly in cells differentiated in KO-DMEM for both EB and monolayer protocols; the highest level was in cultures using the EB protocol. The highest cell proliferation rate was observed using the monolayer/KO-DMEM protocol and the lowest using the EB/DMEM protocol. Generally, KO-DMEM exhibited the greatest impact on germ cell differentiation and cell proliferation. Optimization of germ cell differentiation of ES cells requires careful selection of culture medium.

The Role of Pontin and Reptin in Cellular Physiology and Cancer Etiology

Pontin (RUVBL1, TIP49, TIP49a, Rvb1) and Reptin (RUVBL2, TIP48, TIP49b, Rvb2) are highly conserved ATPases of the AAA+ (ATPases Associated with various cellular Activities) superfamily and are involved in various cellular processes that are important for oncogenesis. First identified as being upregulated in hepatocellular carcinoma and colorectal cancer, their overexpression has since been shown in multiple cancer types such as breast, lung, gastric, esophageal, pancreatic, kidney, bladder as well as lymphatic, and leukemic cancers. However, their exact functions are still quite unknown as they interact with many molecular complexes with vastly different downstream effectors. Within the nucleus, Pontin and Reptin participate in the TIP60 and INO80 complexes important for chromatin remodeling. Although not transcription factors themselves, Pontin and Reptin modulate the transcriptional activities of bona fide proto-oncogenes such as MYC and β-catenin. They associate with proteins involved in DNA damage repair such as PIKK complexes as well as with the core complex of Fanconi anemia pathway. They have also been shown to be important for cell cycle progression, being involved in assembly of telomerase, mitotic spindle, RNA polymerase II, and snoRNPs. When the two ATPases localize to the cytoplasm, they were reported to promote cancer cell invasion and metastasis. Due to their various roles in carcinogenesis, it is not surprising that Pontin and Reptin are proving to be important biomarkers for diagnosis and prognosis of various cancers. They are also current targets for the development of new therapeutic anticancer drugs.

Emerging methods to generate artificial germ cells from stem cells

Germ cells are responsible for the transmission of genetic and epigenetic information across generations. At present, the number of infertile couples is increasing worldwide; these infertility problems can be traced to environmental pollutions, infectious diseases, cancer, psychological or work-related stress, and other factors, such as lifestyle and genetics. Notably, lack of germ cells and germ cell loss present real obstacles in infertility treatment. Recent research aimed at producing gametes through artificial germ cell generation from stem cells may offer great hope for affected couples to treat infertility in the future. Therefore, this rapidly emerging area of artificial germ cell generation from nongermline cells has gained considerable attention from basic and clinical research in the fields of stem cell biology, developmental biology, and reproductive biology. Here, we review the state of the art in artificial germ cell generation.

Differential gene expression profiling of enriched human spermatogonia after short- and long-term culture

This study aimed to provide a molecular signature for enriched adult human stem/progenitor spermatogonia during short-term (<2 weeks) and long-term culture (up to more than 14 months) in comparison to human testicular fibroblasts and human embryonic stem cells. Human spermatogonia were isolated by CD49f magnetic activated cell sorting and collagen(-)/laminin(+) matrix binding from primary testis cultures obtained from ten adult men. For transcriptomic analysis, single spermatogonia-like cells were collected based on their morphology and dimensions using a micromanipulation system from the enriched germ cell cultures. Immunocytochemical, RT-PCR and microarray analyses revealed that the analyzed populations of cells were distinct at the molecular level. The germ- and pluripotency-associated genes and genes of differentiation/spermatogenesis pathway were highly expressed in enriched short-term cultured spermatogonia. After long-term culture, a proportion of cells retained and aggravated the "spermatogonial" gene expression profile with the expression of germ and pluripotency-associated genes, while in the majority of long-term cultured cells this molecular profile, typical for the differentiation pathway, was reduced and more genes related to the extracellular matrix production and attachment were expressed. The approach we provide here to study the molecular status of in vitro cultured spermatogonia may be important to optimize the culture conditions and to evaluate the germ cell plasticity in the future.

Identification of biomarkers for esophageal squamous cell carcinoma using feature selection and decision tree methods

Esophageal squamous cell cancer (ESCC) is one of the most common fatal human cancers. The identification of biomarkers for early detection could be a promising strategy to decrease mortality. Previous studies utilized microarray techniques to identify more than one hundred genes; however, it is desirable to identify a small set of biomarkers for clinical use. This study proposes a sequential forward feature selection algorithm to design decision tree models for discriminating ESCC from normal tissues. Two potential biomarkers of RUVBL1 and CNIH were identified and validated based on two public available microarray datasets. To test the discrimination ability of the two biomarkers, 17 pairs of expression profiles of ESCC and normal tissues from Taiwanese male patients were measured by using microarray techniques. The classification accuracies of the two biomarkers in all three datasets were higher than 90%. Interpretable decision tree models were constructed to analyze expression patterns of the two biomarkers. RUVBL1 was consistently overexpressed in all three datasets, although we found inconsistent CNIH expression possibly affected by the diverse major risk factors for ESCC across different areas.

Generation of germ cells in vitro in the era of induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are stem cells that can be artificially generated via "cellular reprogramming" using gene transduction in somatic cells. iPSCs have enormous potential in stem-cell biology as they can give rise to numerous cell lineages, including the three germ layers. An evaluation of germ-line competency by blastocyst injection or tetraploid complementation, however, is critical for determining the developmental potential of mouse iPSCs towards germ cells. Recent studies have demonstrated that primordial germ cells obtained by the in vitro differentiation of iPSCs produce functional gametes as well as healthy offspring. These findings illustrate not only that iPSCs are developmentally similar to embryonic stem cells (ESCs), but also that somatic cells from adult tissues can produce gametes in vitro, that is, if they are reprogrammed into iPSCs. In this review, we discuss past and recent advances in the in vitro differentiation of germ cells using pluripotent stem cells, with an emphasis on ESCs and iPSCs. While this field of research is still at a stage of infancy, it holds great promises for investigating the mechanisms of germ-cell development, especially in humans, and for advancing reproductive and developmental engineering technologies in the future.

Single cell analysis facilitates staging of Blimp1-dependent primordial germ cells derived from mouse embryonic stem cells

The cell intrinsic programming that regulates mammalian primordial germ cell (PGC) development in the pre-gonadal stage is challenging to investigate. To overcome this we created a transgene-free method for generating PGCs in vitro (iPGCs) from mouse embryonic stem cells (ESCs). Using labeling for SSEA1 and cKit, two cell surface molecules used previously to isolate presumptive iPGCs, we show that not all SSEA1+/cKit+ double positive cells exhibit a PGC identity. Instead, we determined that selecting for cKit^bright cells within the SSEA1+ fraction significantly enriches for the putative iPGC population. Single cell analysis comparing SSEA1+/cKit^bright iPGCs to ESCs and embryonic PGCs demonstrates that 97% of single iPGCs co-express PGC signature genes Blimp1, Stella, Dnd1, Prdm14 and Dazl at similar levels to e9.5–10.5 PGCs, whereas 90% of single mouse ESC do not co-express PGC signature genes. For the 10% of ESCs that co-express PGC signature genes, the levels are significantly lower than iPGCs. Microarray analysis shows that iPGCs are transcriptionally distinct from ESCs and repress gene ontology groups associated with mesoderm and heart development. At the level of chromatin, iPGCs contain 5-methyl cytosine bases in their DNA at imprinted and non-imprinted loci, and are enriched in histone H3 lysine 27 trimethylation, yet do not have detectable levels of Mvh protein, consistent with a Blimp1-positive pre-gonadal PGC identity. In order to determine whether iPGC formation is dependent upon Blimp1, we generated Blimp1 null ESCs and found that loss of Blimp1 significantly depletes SSEA1/cKit^bright iPGCs. Taken together, the generation of Blimp1-positive iPGCs from ESCs constitutes a robust model for examining cell-intrinsic regulation of PGCs during the Blimp1-positive stage of development.

RPAP3 interacts with Reptin to regulate UV-induced phosphorylation of H2AX and DNA damage

We have previously reported that Monad, a novel WD40 repeat protein, potentiates apoptosis induced by tumor necrosis factor-alpha and cycloheximide. By affinity purification and mass spectrometry, RNA polymerase II-associated protein 3 (RPAP3) was identified as a Monad binding protein and may function with Monad as a novel modulator of apoptosis pathways. Here we report that Reptin, a highly conserved AAA + ATPase that is part of various chromatin-remodeling complexes, is also involved in the association of RPAP3 by immunoprecipitation and confocal microscopic analysis. Overexpression of RPAP3 induced HEK293 cells to death after UV-irradiation. Loss of RPAP3 by RNAi improved HeLa cell survival after UV-induced DNA damage and attenuated the phosphorylation of H2AX. Depletion of Reptin reduced cell survival and facilitated the phosphorylation on H2AX. These results suggest that RPAP3 modulates UV-induced DNA damage by regulating H2AX phosphorylation.

Modelling germ cell development in vitro

Germ cells have a critical role in mediating the generation of genetic diversity and transmitting this information across generations. Furthermore, gametogenesis is unique as a developmental process in that it generates highly-specialized haploid gametes from diploid precursor stem cells through meiosis. Despite the importance of this process, progress in elucidating the molecular mechanisms underpinning mammalian germ cell development has been retarded by the lack of an efficient and reproducible system of in vitro culture for the expansion and trans-meiotic differentiation of germline cells. The dearth of such a culture system has rendered the study of germ cell biology refractory to the application of new high-throughput technologies such as RNA interference, leaving in vivo gene-targeting approaches as the only option to determine the function of genes believed to be involved in gametogenesis. Recent reports detailing the derivation of gametes in vitro from stem cells may provide the first steps in developing new tools to solve this problem. This review considers the developments made in modelling germ cell development using stem cells, and some of the challenges that need to be overcome to make this a useful tool for studying gametogenesis and to realize any future clinical application.

Comparative proteome, transcriptome, and genome analysis of a gonadal and an extragonadal germ cell tumor cell line

Whereas clinical differences between testicular and extragonadal germ cell tumors (GCT), like reduced cisplatin sensitivity of extragonadal tumors, are well-established, little is known about underlying tumor biology. A combined approach using global proteome analysis and RT-PCR to assess mRNA levels of selected proteins on the one hand, and array comparative genomic hybridization (array-CGH), on the other hand, was used to compare two germ cell tumor (GCT) cell lines showing embryonal carcinoma histology, one of testicular, and one of extragonadal origin. Overall, the two cell lines show remarkably similar protein profiles. In total, 66 proteins were found to be differentially expressed in an at least 2-fold manner. Of these, 35 proteins (53%) could be positively identified by peptide mass fingerprinting and database search. mRNA levels of 27 differentially expressed proteins were analyzed by RT-PCR. In 17/27 genes (63%), differences in mRNA expression corresponded with differences detected on protein level, suggesting that these proteins are mainly regulated through transcription. Interestingly, no close correlation was found between proteomic and genomic analysis: 13/30 genes (43%) with higher protein levels in one cell line showed higher copy numbers of the respective gene loci in array-CGH analysis. Corresponding differences from proteome, transcriptome, and mRNA analyses were found in 9 of 27 proteins (33%). Several proteins potentially involved in cisplatin resistance were identified in the extragonadal cell line, suggesting that the cisplatin-resistant phenotype of this cell line is multifactorial. Furthermore, our data demonstrate that a combined approach of proteome, transcriptome, and genome analysis is a promising tool to gain information on gene regulation in human tumors.

Gametes from Embryonic Stem Cells: A Cup Half Empty or Half Full?

When first reported 4 years ago, gametogenesis from embryonic stem (ES) cells promised an accessible in vitro model to facilitate molecular analysis of the germ lineage. Formation of primordial germ cells is robust, but terminal gametogenesis remains inefficient and doubts about gamete function persist. Although useful for research, clinical use of ES cell-derived gametes appears a distant prospect.

Identification of transcriptionally regulated genes in response to cellular iron availability in rat hippocampus

The present study was attempted to identify transcriptionally regulated genes of the normal neurocytes responsive to iron availability. Postnatal rat hippocampus cells were primarily cultured either under the iron-loaded or depleted conditions. These cultured cells were applied for the generation of subtracted complementary DNA libraries by the suppression subtraction hybridization (SSH) and for the subsequent identification of differentially expressed transcripts by reverse Northern blot. The differentially expressed genes were chosen to perform sequencing, and then some of them were performed by Northern blot analysis for observation of their expression in the hippocampus of rats with the different iron status. The results indicated that five unique transcripts were strong candidates for differential expression in cellular iron repletion, one of them is a novel sequence (GenBank No. AF 433878), while 26 unique transcripts were strong candidates for differential expression in cellular iron deprivation, one of them is a novel sequence (GenBank No. AY 912101). The revealed known genes responsive to iron availability were previously unknown to respond to iron availability, or have not been determined in the brain, have not even been currently determined in their physiological and biological functions. Interestingly, the proteins encoded by most of the known genes are either directly pointed to or indirectly associated with the molecules that play important, even key roles in cellular signal transduction and the cell cycle. These findings lead to the important suggestion that the cellular responses to iron availability involve extensive transcriptional regulation and cellular signal transduction. Therefore, iron may serve as a signal, which directly and/or indirectly regulates or modulates cell functions.

In vitro generation of germ cells from murine embryonic stem cells

The demonstration of germ cell and haploid gamete development from embryonic stem cells (ESCs) in vitro has engendered a unique set of possibilities for the study of germ cell development and the associated epigenetic phenomenon. The process of embryoid body (EB) differentiation, like teratoma formation, signifies a spontaneous differentiation of ESCs into cells of all three germ layers, and it is from these differentiating aggregates of cells that putative primordial germ cells (PGCs) and more mature gametes can be identified and isolated. The differentiation system presented here requires the differentiation of murine ESCs into EBs and the subsequent isolation of PGCs as well as haploid male gametes from EBs at various stages of differentiation. It serves as a platform for studying the poorly understood process of germ cell allocation, imprint erasure and gamete formation, with 4-6 weeks being required to isolate PGCs as well as haploid cells.

Thioredoxin in the cardiovascular system

The thioredoxin (TRX) system (TRX, TRX reductase, and NADPH) is a ubiquitous thiol oxidoreductase system that regulates cellular reduction/oxidation (redox) status. The impairment of cell redox state alters multiple cell pathways, which may contribute to the pathogenesis of cardiovascular disorders including hypertension, atherosclerosis, and heart failure. In this manuscript, we review the essential roles that TRX plays by limiting oxidative stress directly via antioxidant effects and indirectly by protein-protein interactions with key signaling molecules such as thioredoxin interacting protein (TXNIP). TRX and its endogenous regulators may represent important future targets to develop clinical therapies for diseases associated with oxidative stress.